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Functional Vs Isokinetic Fatigue Protocol: Effects On Time to Stabilization, Peak Vertical Ground Reaction Forces, and J...


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FUNCTIONAL VS ISOKINETIC FATIGUE PROTOCOL: EFFECTS ON TIME TO STABILIZATION, PEAK VERTICAL GROUND REACTION FORCES, AND JOINT KINEMATICS IN JUMP LANDING BY ERIK A. WIKSTROM A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN EXERCISE AND SPORT SCIENCES UNIVERSITY OF FLORIDA 2003

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ii ACKNOWLEDGMENTS Writing this thesis has been one of th e most challenging and demanding endeavors of my academic career, and I could not have done so without the help and support of several important people. Most importantly, I would like to thank Dr. Mike Powers, my committee chair, who encouraged my ideas and supported my efforts throughout the entire process. His ideas and challenges help me to grow both as a student and as a researcher and make this the best possible study that it could be. The rest of my committee also deserves a lot of appreciation. Dr. Mark Tillman was vital in familiarizing me with the lab a nd equipment that were required to complete this study. I would also like to thank Dr. T illman for all his time and expertise helping me troubleshoot the numerous problems that were encountered along the way. I also appreciate and thank Dr. Marybeth Horodyski for her continued support and insight into the entire master’s thesis process. I would also like to take th is opportunity to thank doctoral student Gary Porter for his time that was spent revising my chapters and advising me duri ng the whole writing process. Lastly I would like to thank my friends and family whose constant support and encouragement were invaluable to me in completing this thesis and keeping me sane when the bear was winning.

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iii TABLE OF CONTENTS page ACKNOWLEDGMENTS..................................................................................................ii LIST OF TABLES.............................................................................................................vi LIST OF FIGURES.........................................................................................................viii ABSTRACT....................................................................................................................... ..x CHAPTER 1 INTRODUCTION........................................................................................................1 Statement of the Problem..............................................................................................2 Hypotheses....................................................................................................................2 Definition of Terms......................................................................................................3 Assumptions.................................................................................................................4 Limitations.................................................................................................................... 4 Significance..................................................................................................................4 2 REVIEW OF LITERATURE.......................................................................................6 Introduction................................................................................................................... 6 Talocrural Joint.............................................................................................................7 Time to Stabilization...................................................................................................10 Measurement of Postural Sway..................................................................................14 Ground Reaction Forces.............................................................................................15 Fatigue Protocols........................................................................................................17 Conclusion..................................................................................................................21 3 METHODS.................................................................................................................23 Subjects....................................................................................................................... 23 Instrumentation...........................................................................................................23 Medical Eligibility Form.....................................................................................23 Vertical Jump Station..........................................................................................23 Isokinetic Dynamometer.....................................................................................24 Triaxial Force Plate.............................................................................................24 Infrared Timing Device.......................................................................................24 Motion Analysis System......................................................................................24

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iv Measurements.............................................................................................................25 Time to Stabilization...........................................................................................27 Ground Reaction Forces......................................................................................28 Motion Analysis..................................................................................................28 Isokinetic Fatigue Protocol.........................................................................................30 Functional Fatigue Protocol........................................................................................33 The SEMO Agility Drill......................................................................................33 Plyometric Box Jumps.........................................................................................33 Two-legged Hop Sequence..................................................................................34 Side-to-side Bounds.............................................................................................34 Mini-tramp...........................................................................................................34 Co-contraction Arc..............................................................................................34 Procedure....................................................................................................................35 Data Analysis..............................................................................................................38 4 RESULTS...................................................................................................................40 Introduction.................................................................................................................40 Subjects....................................................................................................................... 40 Time to Stabilization...................................................................................................41 Vertical................................................................................................................41 Medial/Lateral.....................................................................................................41 Anterior/Posterior................................................................................................42 Ground Reaction Forces.............................................................................................42 Joints Kinematics........................................................................................................43 Dorsiflexion.........................................................................................................43 Knee Flexion.......................................................................................................44 Knee Valgum.......................................................................................................44 Correlational Analysis................................................................................................45 5 DISCUSSION.............................................................................................................47 Fatigue........................................................................................................................ 47 Jump Landing Protocol...............................................................................................50 Validity of Measure....................................................................................................52 Ground Reaction Forces.............................................................................................53 Joint Kinematics.........................................................................................................54 Correlation..................................................................................................................54 Indications...................................................................................................................5 4 Conclusions.................................................................................................................55 Summary.....................................................................................................................55 Implications for Future Research................................................................................56 APPENDIX A LETTER OF INFORMED CONSENT......................................................................58

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v B MEDICAL ELIGIBILITY QUESTIONAIRE...........................................................61 C DATA COLLECTION FORMS.................................................................................62 D ANOVA TABLES......................................................................................................64 E RAW DATA TABLES...............................................................................................67 Isokinetic Protocol Data.............................................................................................68 Functional Protocol Data............................................................................................70 LIST OF REFERENCES...................................................................................................72 BIOGRAPHICAL SKETCH.............................................................................................77

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vi LIST OF TABLES Table page 4-1 Vertical TTS as determined by vertical GRF-Fz (mean SD).................................41 4-2 Medial/Lateral TTS as determined by GRF-Mx (mean SD).................................41 4-3 Anterior/Posterior TTS as determined by GRF-My (mean SD)...........................42 4-4 Toe Strike-F1 as determined by GRF-Fz (mean SD).............................................43 4-5 Heel Strike-F2 as determined by GRF-Fz (mean SD)...........................................43 4-6 Ankle Flexion (mean SD)......................................................................................44 4-7 Knee Flexion (mean SD)........................................................................................44 4-8 Knee Valgum (mean SD)......................................................................................45 4-9 Pearson Product Moment Correlation (r and significance)......................................46 D-1 Vertical TTS ANOVA table.....................................................................................64 D-2 Medial/Lateral TTS ANOVA table..........................................................................64 D-3 Anterior/Posterior TTS ANOVA table....................................................................64 D-4 GRF-F1 ANOVA table............................................................................................65 D-5 GRF-F2 ANOVA table............................................................................................65 D-6 Ankle Flexion ANOVA table...................................................................................65 D-7 Knee Flexion ANOVA table....................................................................................65 D-8 Knee Valgum ANOVA table...................................................................................66 E-1 Subject Demographics..............................................................................................67 E-2 Pretest Isokinetic Data..............................................................................................68 E-3 Posttest Isokinetic Data............................................................................................69

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vii E-4 Pretest Functional Data............................................................................................70 E-5 Posttest Functional Data...........................................................................................71

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viii LIST OF FIGURES Figure page 2-1 Anterior view of ankle mortaise...............................................................................10 2-2 Medial or Deltoid ligament of the ankle..................................................................10 2-3 Lateral ligaments of the ankle..................................................................................10 2-4 Force time history of a flat foot landing...................................................................17 2-5 Force time history of a toe to heel landing...............................................................17 3-1 Vertec jump station..................................................................................................25 3-2 Isokinetic dynamometer...........................................................................................25 3-3 Bertec triaxial forceplate..........................................................................................25 3-4 Brower infrared timing device.................................................................................26 3-5 JVC low speed motion recorder camera..................................................................26 3-6 Jump protocol...........................................................................................................30 3-7 Graphical representation of sequential estimation...................................................30 3-8 Vertical time to stab ilization analysis method.........................................................31 3-9 Force time history curve with GRF collection points highlighted...........................31 3-10 Camera setup for motion analysis............................................................................32 3-11 Placement of reflective markers...............................................................................32 3-12 Subject position for isokinetic fatigue protocol.......................................................35 3-13 SEMO agility drill....................................................................................................35 3-14 Plyometric box jumps...............................................................................................36 3-15 Two-legged hop sequence........................................................................................36

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ix 3-16 Side-to-side bounds..................................................................................................36 3-17 Mini-tramp jumps.....................................................................................................37 3-18 Co-contraction arc drill............................................................................................37 5-1 Peak vertical GRF at heel strike (F2).......................................................................53

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x Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science in Exercise and Sport Sciences FUNCTIONAL VS ISOKINETIC FATIGUE PROTOCOL: EFFECTS ON TIME TO STABILIZATION, PEAK VERTICAL GROUND REACTION FORCES, AND JOINT KINEMATICS IN JUMP LANDING By Erik A Wikstrom May 2003 Chair: Michael E. Powers Major Department: Exercise and Sport Sciences Dynamic stability provides inherent prot ection against joint injury and several studies have examined the influence of fatigue on neuromuscular control and joint stability. Thus, the purpose of this study was to compare the effects of an isokinetic(IFP) and functional fatigue protocol (FFP) on stabilization time (TTS), ground reaction forces (GRF) and joint angles following a jump landi ng. Twenty healthy subjects (age=221.6 yrs, height=173.8410.452 cm, mass=67.1312.426 kg) were assessed for the designated events. Subjects completed three jump landi ng tasks, requiring a two-legged jump at 50% of their maximum jump height to the cen ter of a force plate 70cm from the starting position. Immediately following, each subject completed either the FFP or the IFP. Fatigue was considered to have occurred wh en time to completion of the FFP increased to 150% of the initial time to completion or failure to produce 50% of the initial IFP peak torque. Immediately following fatigue, post te sting was performed. TTS was determined

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xi as the point where the sequential average of the vertical ground reaction force data points fell within .25 standard deviations from the me an of the initial 3-sec collection period. Two way repeated measures ANOVA reveal ed no significant differences when comparing isokinetic to functional fatigue values for verti cal TTS [F(1,19)= 3.93, p=.538], medial/lateral TTS[F(1,19)= .287, p=.598] anterior/posterior TTS [F(1,19)= .001, p=.978], toe touch GRF [F(1,19)=.121, p=. 286], and heel strike GRF (F=3.673, p=.070). Also, no significant differences were revealed when comparing the fatigue protocols for ankle Dorsiflexion [F(1 ,19)= .06, p=.803], knee flexion [F(1,19)= .21, p=.652], and knee valgum [F(1,19)= .79, p=.386]. The results of this investigation suggest th at the specific fatigue protocol used did not impair dynamic stability and that future research should focus on fatigue that occurs during athletic competition and the correctness of the measure of time to stabilization.

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1 CHAPTER 1 INTRODUCTION Athletes at all levels of competition may eventually suffer from an ankle injury. While the exact cause of thes e injuries is unknown, a vital component of preventing an injury is the athlete’s neurom uscular control. Neuromuscular control is dependent on the central nervous system (CNS) to interpret and integrate proprioceptive and kinesthetic information. This information identifies the joint’s ability to sense its position in space and to sense motion of the corresponding body segments.1-3 After receiving this information, the CNS must then control indivi dual muscles and respec tive joints involved in specific motions to produ ce safe coordinated movement.2,4 While all aspects of neuromuscular control are important to athletes in preventing and re habilitating injuries, postural control has been have been demonstrated to be important. Athletes who have better postural sway are less likely to suffer ankle injuries in subsequent athletic seasons.5-7 Postural control is a comple x coordination of sensory and biomechanical information and muscul ar exertion on external forces.2,8-11 A loss of any of these factors can lead to increased postural sway and a d ecreased ability to control a body part or the body as a whole during athletic activity. Time to stabilization is the body’s abili ty to minimize postural sway when transitioning from a dynamic to static state, thus a very functional test.12,13 As a form of postural control, TTS involves a complex c oordinated effort betw een the sensory and mechanical systems of the body as well as a se ries of powerful contractions of lower leg musculature and synergistic stabili zers throughout the lower extremity.10

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2 It has been suggested that even healthy athletes may suffer lower extremity injuries during an athletic event due to the fatigue of those muscle s resulting in a decrease in neuromuscular control.9,14-16 These studies focused on lowe r extremity fatigue induced isokinetically. Thus, fatigue c ould be quantified as a percent of peak torque. Yet, very little research has focused on neuromuscula r control following a functional fatiguing protocol. Statement of the Problem Many authors have studied the effects of muscular fatigue on postural control by isokinetically fatiguing their subject’s lower extremity musculature.9,16-18 These studies have generally shown an increase in postural sway after muscular fatigue. However, very little research has examined functional fatigue protocols19,20 of the ankle and their effects on time to stabilization, a more functional test of postural co ntrol. Thus, the purpose of this study is to compare and correlate an is okinetic fatigue protocol’s effects on TTS, peak vertical ground reaction forces and bi omechanical effects (i.e., ankle and knee flexion and knee valgum) duri ng a single-leg-hop stabilizat ion test to those of a functional fatigue protocol, which is simila r to actual athletic practice and game situations. Hypotheses There have been three hypotheses made for this investigation. All subjects performing fati gue protocols (i.e., isokinet ic, functional) will have significant increases in time to stabilizat ion, peak vertical ground reaction forces, and stated biomechanical effects as compared to the pretest measure. There will be a significant increase in subjects’ time to st abilization, peak ground reaction forces, and stated biomechanical effects following the functional fatigue protocol as compared to the is okinetic fatigue protocol.

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3 There will be a high correlation between peak vertical ground reaction forces and time to stabilization in both the pretes t and posttest of both fatigue protocols. Definition of Terms The following terminology will be referre d to throughout this research study. These definitions are provided to clarify th e exact parameters that were being studied. Functional fatigue protocol: Related to the muscular exertion of the lower extremity when performing a sports-specific se ries of agility drills in an effort to establish a reliable applicati on to athletes in competiti on. The protocol in this experiment incorporates the: SEMO agility drill, plyometric box jumps, two-legged hop sequence, side-to-side bounds, mini-tra mpoline balance series, and the cocontraction arc drill. Isokinetic fatigue protocol: Chosen for its inherent ob jectivity, patient safety, and reproducibility. It is related to the musc ular exertion of the lower extremity when performing a series of isokinetic maximal contractions. The protocol for this experiment incorporates continuous maxi mal concentric contractions of dorsi flexion and plantar flexion at the ankle.12 Postural control: A measure of balance or postura l stability. It is the amount a body’s center of mass m oves within or around its base of support.11,21 Proprioception: The awareness of postural movement, the changes in equilibrium, and the knowledge of position, weight, and resistance of objects in relation to the body.1,8 Stability: The ability to transfer vertical projection of the center of gravity to the supporting base while keeping th e knee as still as possible.12 Stabilometry: The common means of objectively de tecting proprioceptive deficits and quantitatively measuring aspects of proprioception.22 Time to stabilization: A valid and reliable technique to measure balance. The method involves landing on a force plate fr om a dynamic state, and transitioning balance into a static state.12,13,23 Peak vertical ground reaction force: The maximum force or heaviness of a landing. Measured in newtons, it accurately depicts how hard or soft an individual landed from a jump. Ground reaction forces are often expressed as the magnitude of the peak vertical force divided by the subject’s body weight, or units of body weight.24 Biomechanical Effects: The changes that occur in jo int angles (i.e., ankle flexion, knee flexion, and knee valgum) from a non-fatigued to a fatigued jump landing.

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4 Assumptions There are six assumptions made for this research study. All subjects were truthful in reporting previous history of lower extremity and head injury and disorders that affect equilibrium. All subjects will give a maximal effort during their testing and treatments. Results of this study are repr esentative of all individuals with no prior history of lower extremity and head injury an d disorders affecting equilibrium. That the functional fatigue protocol was an effec tive method of fatiguing the musculature of the lower leg. That the isokinetic and functional fatigue pr otocols were equivalent in their ability to each fatigue their subjects to the level required, so as not to skew the results. That the testing protocol mimics actual at hletic activity and is an accurate measure of time to stabilization. Limitations There are five limitations identi fied for this research study. Subjects wore different bra nds of shoes, although all a similar style during the fatigue protocols. Subjects were not familiar with the fatigue protocols. Subjects were not familiar with the testing procedures. Only one type of isokinetic fatigue protocol was used. Only one type of functional fatigue protocol was used. Significance This study will test an isokinetic fatigue pr otocol of the lower leg musculature and its effects on time to stabilizat ion and peak vertical ground reac tion forces as compared to a functional fatigue protocol of the lower le g musculature. Through the examination of the main effects of the fatigue protocols and the tests performed, a highly positive correlation will be illustrated. More importa ntly, a significant difference in the main

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5 effects and the interaction of th e fatigue and tests (i.e., time to stabilization, peak vertical ground reaction forces, biomechanical effects) will strongly suggest that isokinetic fatigue protocols do not mimic functional activit y. These results will provide practical, clinical applications, rega rding how functional fatigue increase time to stabilization, allowing clinicians to focus on improving postu ral control in their athletes. However, these results will also benefit researchers indicating that a functional fatigue protocol is a more reliable method of mimicking the fatigue that takes place duri ng athletic activity.

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6 CHAPTER 2 REVIEW OF LITERATURE Introduction Injuries to the ankle or talocrural joint can occur in any sport because the ankle is the focal point to which total body wei ght is transmitted to during ambulation.25 Therefore the talocrural joint is one of the most common areas for injury in the athletic population, specifically the stabil izing ligaments of the joint.7,22,26-33 Starkey33 reviewed injury data over a span of ten years for the NBA, and found that the most common site of injury was the ankle joint. Ankle injuries accounted for more than 10% of all injury occurrences, and 11% of time lost due to in juries. Similar observations have been reported elsewhere.28,29 According to Ekstrand and Tropp29 approximately 40% of all injuries occur at the ankle joint. Anecdotall y, most of these injuries occur at the end of activity when the athlete is fatigued.16 Ankle sprains, which affect the stab ilizing ligaments, ar e caused by sudden inversion or eversion forces that overwhelm the ankle’s defenses (i.e., proprioception, muscular strength).25 These forces are often combined with plantar flexion and result in the stretching or tearing of the peron eal muscles and or stabilizing ligaments3 While relatively minor injuries, ankle sprains can result in a great deal of missed athletic participation. Therefore, measures to pr event the mechanisms of injury need to be studied to reduce or pr event ankle injuries as much as possible. Several theories have been explored as to the cause of ankle injury. These causes can be broken into extrin sic and intrinsic factors3,4,30 Extrinsic factors include poor

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7 equipment, improper shoes and playing surf ace. Intrinsic factor s include muscular fatigue, excessive pronation and ligament laxit y. All these factors taken individually or in combination can lead to ankle injuries. Muscular fatigue of the lower extremity has been one of the focus of recent studies, in an attempt to better unders tand its direct effect on ankle and how it predisposes the ankle to injury.9,14-19,34 Fatigue of the lower leg musculature is controversial as to its importance to increasing postural sway. Motor control of an extremity is dependent on proprioceptive feedback and reflexive and voluntary muscle responses.9,35 Muscular fatigue could negatively affect propriocepti on through either deficiencies in the activation of the muscular mechanoreceptors or a decrease in the muscular function. These deficiencies have been credited through a positive correlation between muscular fatigue, quantified as 50% of the initial baseline test, and a d ecrease in postural control during several studies.9,16-19 Most of these correlations have us ed isokinetic fatigue protocols in a nonweight bearing position, and with postural control testing methods and protocols conducted in full-weight bearing positions. Talocrural Joint The ankle joint (talocrural joint) is made up of three bones; th e tibia, fibula and the talus. The tibia, the weight bearing bone of the lower leg, is affixed to the fibula via several ligaments. The distal aspects of these bones (i.e., medial and lateral malleolus) form the ankle mortise (Figure 2-1), in which the head of the talus sits and rocks in an anterior/posterior dir ection during ambulation.3,25,30,36,37 The articulation of this joint forms a str ong preventative measure against medial or eversion ankle sprains because the medial ma lleolus extends signifi cantly more distally than the lateral malleolus which forms a bony block that limits talar abduction. The

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8 anatomical failure of the body to prevent lateral ankle spra ins with bony defenses causes the ligaments and musculature of the lower leg to play a vital role in stabilizing the ankle from lateral sprains. The stabilizing ligaments of the ankle joint, which protect the ankle in three distinct areas and from different moti ons, are the tibiofibular, lateral, and medial. The tibiofibular ligament is the distal and proximal extremes of the interosseous membrane that transverses the entire lower leg, connecting the tibia and fibula.36,37 The oblique arrangement of the tibiofibular ligame nts aid in the distribution of force placed upon the lower leg and stabi lizes the ankle from rota tion forces during activity.3,25,30,37 The medial or deltoid ligament (Figure 2-2) is the primary resistance against eversion of the ankle and is the strongest ligament in the talocrural joint.3,25 The deltoid ligament is actually four ligaments that act as an interconnected fa n, increasing its strength and decreasing its incidence of injury. The ligam ents of the medial aspect of the ankle originate collectively at the medial malleolus of the tibia and insert individually to the talus, calcaneous, and navicular.3,4,30,36,37 The lateral ligaments of the talocrural join t (Figure 2-3) also collectively originate at a common site, the lateral malleolus of the fibula, and insert at the talus and calcaneous. These ligaments, named after thei r respective insertions are the anteriortalofibular (ATF), the calcaneofibular (C F), and the posterior-talofibular (PTF). Individually, none of these la teral-stabilizing ligaments ar e as strong as the deltoid ligament structure.25 The ATF has the highest inciden ce of injury in the ankle joint because it is the first ligament to undergo stress when the ankle is inverted and plantarflexed.11,25 The CF ligament situated vertically is usually only injured during severe grade two ankle sprains, while the PT F ligament is the strongest of the lateral

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9 ligaments and is usually uninjured, excep t in the most severe ankle sprains.25 Collectively these stabilizing ligaments protect the ankle from invers ion forces, while the ATF and PTF also prevent anterior and poste rior translation of the talus in their respective directions.3,11 Supporting the stabilizing ligaments are th e surrounding muscles of the lower leg. These muscles, respective nerves and vasc ular supply are divided into four main compartments that serve different functions.3,25,37 The anterior compartment contains the anterior tibialis and toe extensors, which ar e the primary and secondary dorsiflexors of the foot respectively. The lateral compartment holds the peroneals, which are the main evertors of the foot and prev ent excessive inversion during ac tivity. The posterior tibialis and toe flexors make up the deep posterior compartment, which are secondary invertors and plantar flexors of the foot. The final comp artment is the superficial posterior that is made up of the gastrocnemius and soleus muscles, the main plantar flexors of the foot and main stabilizers of ankle motion.3,4,25 While all the muscles mentioned are important, weakness of the peroneals and ga strocnemius/soleus complex would more significantly put an athlete at risk to injury, specifically to inversion ankle sprains.38,39 The ankle joint, while st able during daily activities undergoes extreme forces during athletic competition, which places increa sing stress at the lateral aspect of the joint. This additional stress is focused on an area that is anatomically weak, increasing the ankle joint’s incidence of injury. The in trinsic factor of muscular fatigue on postural control, becomes increasingly important in th e body’s effort to maintain its center of balance and preventing lateral ankle sp rains, in a weak anatomical area.

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10 Figure 2-1. Anterior view of ankle mort aise; tibia(1), fibula(2), talus(3). Figure 2-2. Medial or Delto id ligament of the ankle Figure 2-3. Lateral ligaments of the ankle.

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11 Time to Stabilization Time to stabilization, a form of postural swa y, is defined as the time that is required to reach stability after landing.10,22 Increased postural sway is a negative factor that can lead to increased incidence of injury cau sed by diminished factors of neuromuscular control and or balance.5,7 Proprioception is defined by Reimann and Lephart2 as the ability of a joint to determine its position in space; detect movement, kinesthesia, and sense resistance acting on it. The impor tance of understanding proprioception and kinesthesia during athletic comp etition is vital to preventing injuries. Without sufficient proprioceptive and kinesthetic awareness, the body would not be able to respond to changes in joint angles, inhibiting the joint’s ability to protect itself from extreme motion or forces that would cause damage to soft tissue or bone. Hoffman and Payne22 and Johnston et al.9 attribute the diminish ed ability to detect motion and joint position sense to a decrease d accuracy of afferent input and efferent output or an increase in musc ular fatigue. The afferents that are responsible for the response time of muscular act ivation, to maintain the body’s center of balance, are mechanoreceptors1,9,11,40 These mechanoreceptors are located in the joints and muscles of the body,1,3,9,11,39,41 and include the joint mechanoreceptors: Ruffini’s endings, Pacinian corpuscles and free nerve endings.1,11,37 The mechanoreceptors interpret the joint’s position and detect a passive or active movement of the joint in both closed and open kinetic chains. Muscle mechanoreceptors, such as muscle spindles and Golgi tendon organs located in the muscles and tendons, ar e responsible for sensing changes in muscle length and tension respectively.1,8,11,40 Together these receptors relay information to the central nervous system (CNS) regarding changes occurring in and around the joint to help keep the body within its center of balance.1,4,11,37,40,42,43 A decrease in the efficiency of

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12 these mechanoreceptors would increase th e latency period of the reacting joint musculature.2,11,30,35,44 An increase in reaction time due to malfunctioning mechanoreceptors allows a joint to be dangerously extended beyond normal anat omical ranges of motion. This contortion is accomplished because the surrounding muscles (i.e., gastrocnemius, peroneals) may not fire as quickly and then could not co rrect the body’s center of balance. This inhibiting factor of mechanor eceptor deficiencies can be complicated further by muscular fatigue. McKinely and Pedotti10 noted that the subjects w ith the shortest time to stabilization had all three major muscles of th e lower leg (gastrocnemius, soleus, anterior tibialis) contracted prior to landing. This contraction creat es greater muscle stiffness, which would allow faster reaction to the la nding surface. Subjects with poor time to stabilization scores showed little to no an ticipatory control cont raction of lower leg musculature as measured by electromyography.10 Aniss et al.45 provided another insight into a decreas ed time to stabilization score. The study examined the various gains of cuta neomuscular reflexes evident in extensor and flexor muscles of the lower leg. These da ta indicated that these reflexes are only present when their respective muscles are in contraction. Aniss et al.45 and McKinely and Pedotti10 indicated that an association exis ts between anticipatory or voluntary contraction of the lower leg musculatur e and a decrease in reaction time for the cutaneomuscular reflexes of the lower leg a nd time to stabilization, respectively. This would decrease time to stabilization and if fatigue decreases force output in musculature,

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13 then pre-landing contraction at the end of an activity might also be decreased and not strong enough to excite the cutaneomuscular reflexes.45 Konradsen et al.39 determined through a clinical e xperiment that the latency period, response to stimulus, of the peroneals was too long to prevent lig amentous overload in the clinical setting. Kondradsen et al.39 also concluded that during activity, the ankle joint and respective musculature receives info rmation from the receptors near the ankle and foot, rather than from visual or ves tibular information, sin ce those sensory inputs were not denied to the subjects during the experiment. This study supports the data collected by McKinely and Pedotti10 and Aniss et al.45 that anticipatory contraction of the lower leg musculature is a prime stabilizing factor of the ankle. Recent studies have reported positive correlations between muscular fatigue and an increase in postural sway and time to stabilization.9,16-19 As stated earlier, time to stabilization, an aspect of motor control for the lower extremity, is dependent on proprioceptive and kinesthetic feedback as well as reflexive and voluntary muscle responses.9 Muscular fatigue would negatively affect this proprioceptive feedback loop through either deficiencies in the activation of the muscul ar mechanoreceptors or a decrease in the force produced by muscul ar function. Decreases in activation of mechanoreceptors increase the latency period of the muscle action and prolongs the time to correction and regaining the individual’s center of balance.10,39,45 Muscular fatigue also decreases the force production of a musc le when measured via isokinetic fatigue protocols.9,14,16-18,46-48 These protocols often indicate a subject is fatigued when peak torque falls below 50% of the initial contraction.9,16,17,19,20 Thus a delayed firing of the

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14 corresponding musculature with a decreased for ce production may exponentially increase injury risk and incidence.7,44,45,49 Because of these data from isokinetic fati gue protocols, there have been several training protocols established to help injured athletes regain proprioception, potentially reducing time to stabilization indirectly. While the protocols vary in specific components, most encompass a single leg balance program, focusing on maintaining the center of gravity within the base of support.11,49 Common ways of training include maintaining center of balance on a stable surf ace and progressing to an unstable surface (i.e., a wobble board). These training progr ams require a signifi cant amount of balance and motor control, while acclimating the mu scle to fatigued conditions. Konradson50 illustrated that proprioceptive training can be 80% effective in reducing the frequency of ankle sprains. Measurement of Postural Sway Training protocols can only be effective and measured if there is a baseline to measure postural sway against. Several valid and reliable testing methods are available including the single leg balance, Balance Error Scoring System and Star Excursion test. However, more functional and dynamic meas ures of time to stabilization can be measured using single-leg-hop stabilization test on force plates. However, according to Reimann35 there is no relationship between static and dynamic measurements of postural sway. One possible technique to measure balance is stabilometry22 often seen in the form of a Biodex stability system (BSS).21,51 Stabilometry is a techni que that utilizes a force plate to measure the displacement of an indi vidual’s center of gravity while standing in a

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15 static state. While indicating a reliable meas ure of balance, these data points were also comparable to studies performed using static force plates.21 Force plates are more often used to determine stability12-center of pressure or ground reaction forces for a single limb stance.12,13,51 These measurements are obtained though measuring force at three or more point s on the platform or the torque around the horizontal axes.7,13 Time to stabilization is a func tional exam of stability by definition, forcing subjects to maintain balance through a transition from a dynamic to a static state.13 Two common methods for this transi tion are the step down or hop tests. Respectively, the subject would step down off an elevated pl atform or hop a set distance with a minimum height requirement, land on th e force plate and rega in their center of balance.12,52 Goldie et al.53 developed a testing protocol th at was reliable and minimized lost data due to subject mortality. This pr otocol also noted that ground reaction forces produced more reliable results than center of pressure scores.13,51,53 Ground Reaction Forces Ground reaction forces (GRF) are a method of measuring balance by measuring the torque around two horizonta l and one vertical axes.13 These forces are indicators of how heavily an athlete lands from a jump, and how well they balance in a stance, making a good measure of the time it takes that athlet e to stabilize their body mass within their center of gravity. GRF acting on the body duri ng landings have been associated with injury to the lower limb.24,26 Ground reaction forces and center of pressure measures have been used repeatedly in single stance tests of balance a nd stabilometry. Goldie et al.13 found that GRF were more reliable indicators of balance and stabiliz ation of the subject than center of pressure measures. Previous studies ha ve also shown the reliability of this measure to be high.

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16 Ground reaction forces are often expressed as the magnitude of the peak vertical force divided by the subject’s body wei ght, or units of body weight.24 There are two common appearances of ground reaction forces, that of athletes who land flat footed (Figure 2-4), and that of athletes who la nd with a toe-heel technique (Figure 2-5).26 The flatfoot method produces a un imodal, while the toe-heel method produces a bimodal ground reaction force-time history.26 The more practiced landing technique, the toe-heel, produces to maximu m force outputs on the bimodal curve from forefoot and heel contact respectively.26,54 Recent studies have shown peak vertical GRFs as high a 6.0BW.26 However, little research has been done to illustrate the effects of fatigue on GRF, most of the research has focused on style of jump, and landing technique. The effects of fatigue on GRF could be very significant, as joint angles and muscle stiffness at touch down play a major role as to the magnitude of the peak vertical GRF. Landing from any jump requires the body to produce movements which will further minimize the GRFs and soften the landing.10,55 According to Dufek and Bates26, the height of a jump plays a minor role in the magnitude of GRF as co mpared to knee joint angle at touch down. This theory is backed by studies that show a toe-heel landing as opposed to a flatfoot landing, requires gr eater joint flexion to decrease GRFs.24,26 In an attempt to reduce GRF the body must anticipate the landing and prepare for it by increasing muscle stiffness.10,55 Activation of the lower extremity musculature, specifically the triceps surae complex will he lp slow the rate of decent and decrease ground reaction forces on the body. Further re duction of GRFs can be accomplished by allowing the knee and hip to flex more whic h increases the time of landing providing an

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17 attenuation in kinetic energy.10,24,55 A deficiency in the body’s ability to produce anticipatory contractions and eccentrically contract lower extremity musculature in a controlled manner would drastically increase GRF as well as an athlete’s time to stabilization.24 These deficiencies are often cause d by fatigue of the lower extremity through participation in athletic events. Figure 2-4. Force time histor y of a flat foot landing. Figure 2-5. Force time history of a toe to heel landing.

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18 Fatigue Protocols Fatigue protocols are often used to mimi c a subject’s loss of power output during an athletic event. Fatigue is defined as an inability to produce an e xpected force or power output, which negatively affects proprioception through either deficiencies in activation of the muscular mechanoreceptors or a decrease in the muscular function.15 Traditionally, isokinetic fatigue protocols are us ed to mimic the fatigue that occurs during an athletic event. These protocols often quan tify fatigue at 50% of th e initial peak torque generated by the subjects.9,16-18 The testing protocols of pr evious research have been conducted at both high and low angular velociti es and varying repetitions. The isokinetic fatigue protocol ends traditionally when three consecutive repetitions are below 50% of the initial peak torque, to ensure that fatigue and not lack of effort is indicated by the torque values.9,16-18 The purpose of these isokinetic fatigue protoc ols is to isolate pa rticular muscles and to determine each muscle’s role in establ ishing and controlling time to stabilization. Isokinetic testing provid es a fixed speed with a varying resistance to allow for maximal effort throughout a range of motion (ROM).3,4,56 Using isokinetic machines, the ROM of a joint and the strength of a group of muscles can be assesse d. Isokinetic testing provides information such as peak torque, average power and total work done, as well as the subject’s fatigue index. Isokinetics allow at hletes to perform exercises at a more functional speed than isotonic exercise; a fixed resistance, varying speed exercise.3,4 The majority of isokinetic testing is done vi a open kinetic chain (OKC) positioning. An open kinetic chain indicates that the distal extremit y, in this case the foot, is not fixed and can move freely without affecting the performed ex ercise. The counter position is a closed

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19 kinetic chain (CKC) which has the distal extremity, hand or foot, attached to the ground or stable platform.3,20,28,41,47 Open kinetic chain testi ng is non-weight bearing and therefore, does not account for the stabili zing effects that seco ndary and synergistic muscles play during closed kinetic ch ain (CKC) weight-bearing exercises. Bobbert and van Ingen Schenau57 compared the mechanical output of the ankle during isokinetic plantar flexi on and single-leg jumping. The results indicated that at a given angular velocity of plantar flexion much larger moments were produced during jumping than isokinetic plantar flexion.57 Bobbert and van Ingen Schenau57 reasoned that during isokinetic testing the duration of plantar flexion is so short, that the gastrocnemius can not rise to the ma ximum strength potential and produces a submaximal muscle moment. Also the positioning of isokinetic testing places the muscle fibers of the plantar flexors in an unfavorable area of their force-velocity relationship.57 Despite the limitations of isokinetic te sting, several studies have indicated a positive correlation between isokinetic peak torque and functional ability. Wilk et al.48 investigated the relationship between isokinetic knee extens ion strength and functional testing. The results indicated a positive correlation between is okinetic strength and functional ability. The results from Negrete and Brophy47 demonstrated the same relationship. While the da ta indicated a positive corre lation, only the Negrete and Brophy47 results were significant. Similarly, Morgoni et al.46 compared isokinetic peak torque to maximal ball velocity in young soccer players. These data illustrated a significant and positive correlation between isokinetic peak torque and functional ability.

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20 OKC isokinetic fatigue protoc ols have also indicated a positive correlation between fatigue and an increase in pos tural sway. Johnston et al.# indicated significant differences in postural sway after conducting isokinetic fatigue protocols. In another study, Vuillerme et al.15 also indicated significant increa ses in postural sway after muscle fatigue was induced via an isokinetic protocol. Regardless of these correlations, a more clin ically relevant protocol would be CKC, weight-bearing testing. Recently there have be en studies done to investigate close kinetic chain isokinetic testing.9,20,41,47 These studies have suggested positive correlations between the open and closed kinetic chain isokinetic testing protocols.20,47 However, it should be noted that most of these protocols compare peak torque to a maximal strength test. Porter et al.20 conducted a study that illustrated a way to measure standing isokinetic peak torques for dorsiflexion and plantarflexion. In this study, a positive strength correlation was indicated betw een the non-weight and weight-bearing isokinetic test positions. This could indicate that isokinetic testing is a valid and reliable method of measurement, but no correlations have been noted at this time regarding isokinetic fatigue protocols and func tional fatigue protocols. While several other studies have indicated that a positive correlation between isokinetic strength and functional ability does exist, very little research has been done to determine the validity of isoki netic fatigue protocols. To the best knowledge of the researchers, no study has investigated and comp ared the effects of an isokinetic fatigue protocol and a functional fati gue protocol on time to stab ilization. Functional fatigue protocols may consist of any number of CK C weight-bearing activities that include dynamic movement and require stabilizing effects of the musculature. Sprints19, toe

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21 raises15 and cutting34 are just a few examples of functiona l activities that can be used in a fatigue protocol. Though little research has focused on f unctional fatigue protocols, several studies have found that postural control has increased significantly with functional fatigue.12,19 Conclusion The ankle joint, supported by stabilizing ligaments and su rrounding musculature, is the focal point for the body’s weight during ambulation. Due to the significant amount of weight placed upon the joint and the inherent instability of the ankl e, the ankle is the most commonly injured body part during athletic competition.22,24,26,28,33 Ankle sprains, especially lateral, often beco me chronic injuries due to the incomplete rehabilitation process that does not address the decreased neuromuscular control and the increased time to stabilization resul ting from the injury. Time to stabilization, or the amount of tim e for the body to regain the center of balance or mass within it’s base of support, and can be affected by several factors including injury or a prolonged response time to afferent neural signals caused by muscular fatigue. This increased respons e time, quantified in time to stabilization, inhibits the already destabil ized ankle joint during dynamic movement and increases the chance for injury. To determine the increa sed response time, subjects must stabilize themselves on a force plate. The majority of the research investiga ting the effects of muscular fatigue on postural sway and time to stabilization util ized an isokinetic pr otocol. Isokinetic protocols are frequently chosen because of the inherent safety to patients, their objectivity, and their reproducib ility in testing measures.15 However, the validity of isokinetic fatigue protocols has not been a ddressed. To determine if OKC isokinetic

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22 fatigue protocols are a true measure of the fatigue experienced duri ng athletic activity, they must be compared to functional fatigue protocols. Any number of CKC weightbearing activities can be incorporated into a functional fatigue protocol and compared to isokinetic fatigue protocols through the m easurement of time to stabilization.

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23 CHAPTER 3 METHODS Subjects Twenty subjects were asked to voluntarily pa rticipate in this investigation. To be included in this study subjects were between 18 and 30 years of age, and have no prior history of lower extremity or h ead injury within the past year Subjects were excluded if they suffered from any disorders that affect neuromuscular control and were moderately trained. (i.e., exercise 2-4 times per week) All subjects were asked to read a description of the study and sign an informed consent fo rm, approved by the university Institutional Review Board (IRB) (Appendix A). Instrumentation Medical Eligibility Form The eligibility form (Appendix B) was designed to determine eligibility for participation in this study. The questionnaire was completed prior to any data collection. Vertical Jump Station A Vertec vertical jump device (Sports Imports, Columbus, OH) was used to establish subjects’ maximal vertical jump (Fi gure 3-1). All subjects will stand next to the Vertec device and reach as high as possible. This measure was recorded as the subject’s standing height. Subjects will then be asked to jump as high as possible and move the highest vane possible. This height was reco rded as the maximal vertical jump height. All vanes are measured off at 1.27 cm increments.

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24 Isokinetic Dynamometer A Kinetic Communicator (Kin Com) 125 AP (Chattanooga Group, Chattanooga, TN) isokinetic dynamometer integrated with a computer and appropr iate software was used to induce isokinetic fatigue of the planta r and dorsi flexors of the ankle (Figure 3-2). Triaxial Force Plate A Bertec triaxial force plat e as seen in figure 3-3 (B ertec Corporation, Columbus, OH) was used to measure duration of instability from time of impact until pretest values of stability are recorded at a frequency of 600-Hz. The force plate data will undergo an analog to digital conversion and was stored on a PC-type computer using the DATAPAC 2000 (Run Technologies, Laguna Hills, CA) analog data acquisition, processing, and analysis system. Infrared Timing Device A Brower infrared timing device (Browe r Timing Systems, Salt Lake City, UT) was used to time subjects during the functional fatigue protocol. The device transmitters (Figure 3-4) project an infrared beam at the start and finish line of the functional fatigue protocol area. A subject’s time began as th ey crossed and ended as the subject crossed the finish line. The device was used to dete rmine 150% of initial time for each subject. Motion Analysis System Kinematic data was collected using a se t of two JVC low speed motion recorder cameras (US JVC Corporation, Fairfield, NJ) as seen in figure 3-5. This system collects all data at 60Hz from two angles, both posterior lateral and anterior lateral for all trials. A motion analysis will allow additional depe ndent variables of lower extremity joint angles to be measured using Peak Motus motion analysis system (Peak Performance Technologies, Englewood, CO) to digitize all kinematic data.

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25 Figure 3-1. Vertec jump station. Figure 3-2. Isokinetic dynamomete r with integrated computer. Figure 3-3. Bertec triaxial forceplate.

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26 Figure 3-4. Brower infrared ti ming device as set up for the functional fatigue protocol. Figure 3-5. JVC low speed motion recorder camera.

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27 Measurements Time to Stabilization Subjects will start in a standing position 70 cm from the center of the triaxial force plate. Each subject was requi red to jump off of both legs and touch a designated marker placed at a position equivalent to 50% of th e subject’s maximum vertical leap before landing on the force plate52 The subject is to land on thei r stance leg (leg used to plant when kicking a ball), stabilize as quickly as possible and balance for 20 seconds on the triaxial force plate. This protocol can be seen in figure 3-6 below moving from right to left. The average of the three trials were taken as their respective pretest data score. All subjects were instructed to ju mp with their head up and hands in a position to touch the designated marker. Medial /lateral and anterior/posterior stabilization time was determined using the technique of sequentia l estimation (Figure 3-7). The technique incorporates an algorithm to calculate a cumulati ve average of the data points in a series by successively adding in 1 point at a time.12 This cumulative average was compared against the overall series mean, and the series was considered stable when the sequential average remained within standard deviation of the overall series mean.12 The series consists of all data points within the first three seconds of touch down. Vertical TTS was established as the time when the vertical force component reached and stayed within 5% of the subject’s body weight after la nding (Figure 3-8).10 A subject’s body weight was established as the average of the variation of the vertical GRF in the final second of the 20-second data collection period.

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28 Ground Reaction Forces The anteroposterior, mediolateral, and vert ical and the ground r eaction moments about those axes was collected and analyzed at a frequency of 600Hz. The GRFs measured in Newton’s by computer softwa re will accurately depict how hard or soft an individual lands from a ju mp. These GRF measurements are then quantified as an intensity of the land ing, expressed as the magnitude of the peak force divided by the subject’s b ody weight, or units of body weight. Anteroposterior and mediolateral GRF vari ations were used as part of the TTS calculation. The peak vertical ground reaction force intens ity was examined at two points when initial contact with the force plate is made, (F1) forefoot contact and (F2) rearfoot contact within the bimodal curve associated with a toe-heel landing in the force-time history (Figure 3-9).26 Motion Analysis Kinematic data was collected using a set of two JVC motion re corder cameras (US JVC Corporation, Fairfield, NJ). This system collects all data at 60Hz from two angles, both posterior lateral an d anterior lateral for all trials (Figure 3-10). Camera 1 was positioned 5.05-m to the posterior lateral side for subjects landing on their right foot or 6.68-m to the posterior lateral side for subjec ts landing on their left foot, while camera 2 was 5.05-m to the posterior lateral side for s ubjects landing on their right foot or 6.68-m to the posterior lateral side for subjects landing on their left foot. Both cameras were able to view all reflective markers during each la nding task, thus enabling three-dimensional analysis. Reflective markers were placed at th e greater trochanter, mi d thigh, lateral joint line of the knee, mid shank, lateral malleolus, ca lcaneous, and head of the fifth metatarsal (Figure 3-11).57,58 All video data was analyzed us ing a Peak Motus motion analysis system (Peak Performance Technologies, E nglewood, CO). Ankle flexion was seen as the vector angle between the A1-A2 segment (5th metatarsal – calcaneous) and the B1-B2 segment (knee – lateral malleolus). Knee flex ion was then measured as the calculated vector between P1-V-P2. With the greater tr ochanter as P1, the knee as the fulcrum (V) and the lateral malleolus as P2. Knee valgum was determined by the difference of the X

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29 coordinates of the greater troc hanter and knee in the 3D tr ansformed data. The values were taken at the point just prior to touc h down and at all points after touch down. The greatest displacement of the greater trocha nter and knee X coordinates after touchdown and at jump height marker were used to find the difference.

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30 Figure 3-6. Jump protocol from right to left. Starting posit ion, mid-jump and finishing position. Sequential Estimation GRF curve Sequential Estimation 1/4 std of overall series mean Figure 3-7. Graphical representa tion of sequential estimation

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31 Vertical TTS Vertical TTS Body Weight + 5% Body Weight Figure 3-8. Vertical time to stabilization analysis method. Figure 3-9. Force time history curve w ith GRF collection points highlighted.

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32 Figure 3-10. Camera setup for moti on analysis of joint kinematics. Figure 3-11. Placement of reflective markers.

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33 Isokinetic Fatigue Protocol The isokinetic fatigue protocol was admi nistered using the Kincom Isokinetic Dynamometer in the Biomechanics Laboratory (F igure 3-12). Subjec ts were positioned according to manufacturers spec ifications for ankle dorsi and plantar flexion (DF and PF). Each subject will perform 3 sub-maxima l and 3 maximal repetitions for a warm-up, followed by 1 minute of rest. An initial peak torque value w ill then be taken using the overlay mode from the 3 maximal repetitions of DF and PF at 120 and 30 degrees per second respectively.12 The subject will then continue to give a maximal effort with a continuous series of concentric contractions of DF and PF until PF falls below 50% of both the respective peak tor que values for a minimum of 3 consecutive repetitions. Functional Fatigue Protocol Before the functional fatigue protocol is administered each subject was given instructions and practices and a single maximal effort run of the course for a warm-up, followed by 1 minute of rest. The functional fatigue protocol, will consist of the following: The SEMO Agility Drill A series of forward sprints, diagonal back-pedaling, and side stepping within a 12’ x 12’ area (Figure 3-13). (The subject completed 3 repetitions) Plyometric Box Jumps A series of 3 boxes of increasing height, 18” apart (Figure 3-14). The subject must jump onto the first box, stabilize and jump down, immediately jumping back up onto the second box, stabilize and repeat onto the third box. (The subj ect completed 3 repetitions)

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34 Two-legged Hop Sequence A series of markers spaced over a ten foot distance, were jumped onto and immediately off of towards the next marker. The subject must jump and land using both feet for each marker (Figure 3-15).59 (The subject completed 3 repetitions) Side-to-side Bounds An area 5’ wide in which the athlete must jump sideways from the center marker to the one side back to the center and then to the opposite side (Figure 3-16). (The subject completed 30 repetitions) Mini-tramp Subjects must jump onto a mini-tramp, stab ilize and jump off onto the floor on the opposite side (Figure 3-17). (The subject completed 30 repetitions) Co-contraction Arc Subjects must resist the tension of an el astic cord as the side shuffle around a 180degree arc (Figure 3-18).59,60 (The subject comp leted 10 repetitions) Fatigue was quantified as the time that it takes for a 150% increase from their maximal effort run through the course. Time to complete the functional fatigue protocol was measured using infrared sensors that i ndicate the time for the completion of each circuit. Fatigue has been set at 150% to mi mic previous studies on the effects of fatigue on time to stabilization in the literature.19

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35 Figure 3-12. Subject position for isokinetic fatigue protocol Figure 3-13. SEMO agility drill.

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36 Figure 3-14. Plyometric box jumps. Figure 3-15. Two-legged hop sequence Figure 3-16. Side-to-side bounds.

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37 Figure 3-17. Mini-tramp jumps. Figure 3-18. Co-contraction arc drill.

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38 Procedure Each subject will report to the biomechanic s laboratory on two separate occasions. On each occasion subjects were pretested for time to stabilization following a single leg landing on a force plate. Each subject will co mplete either a functional or an isokinetic fatigue protocol immediately following the pre-test. Fatigue pr otocol completion was randomized counterbalanced. Once fatigue has been induced, each subject was reassessed for time to stabilization following procedures identical to those used during pretesting. Additionally a motion analysis of each subject’s landing tech nique was conducted for all pre and posttest trials. This analys is, based on the average of the three trials completed, will compare and contrast the av erage amount of ankle and knee flexion and knee valgum from the two fatigue protocols. Post testing procedures were initiated 30 seconds following completion of the fatigue protocol. When subjects return on the second occasion the same procedures were followed, however, a different fa tigue protocol was used. The ordering of the fatigue protocols were in a randomized counter ba lanced order with a minimum of one week separating testing sessions. Data Analysis The independent variables are the fatigue protocols and test, while the dependent variables will consist of time to stabilization, vertical GRF, and knee and ankle angles. The data was analyzed with two-way analyses of varian ce (ANOVA) with repeated measures. The two within subject variables will include fatigue protocol (isokinetic vs functional) and time (pre-test vs. post test). The means were compared between all

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39 conditions, to determine the main effects of protocol and time. Following the analysis, post hoc testing was conducted using a Tuke y’s HSD test. A Pearson Product Moment Correlation Coefficient was calculated to determine if a relationship exists between the ground reaction forces, time to stabilization, a nd knee and ankle angles. An alpha level was set at .05 for all statistical analyses.

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40 CHAPTER 4 RESULTS Introduction The purpose of this study was to compare the effects of isokinetic and functional fatigue on TTS, peak vertical ground reaction forces and joint angl es during a single-leg jump landing. The isokinetic fatigue pr otocol was adapted from those commonly reported in the literature while the functional fatigue protocol was developed to simulate actual athletic practice and game situations The independent va riables included the fatigue protocol (isokinetic vs functional) and time (prevs post-exercise). The dependent measures included vertical, medi al/lateral, anterior/posterior time to stabilization scores, peak vertical ground r eaction forces (toe st rike, heel strike), maximum ankle, and knee flexion, and maximu m knee valgum. Data were analyzed to identify differences among any of these measures and are presented according to the dependent measure that they represent. Raw data and ANOVA tables are found in Appendices D and E. Subjects Twenty healthy subjects free from lo wer extremity injury, CNS injury and disorders that affect neuromuscular control ove r the past six months. All subjects read a description of the study and signed an inform ed consent form, approved by the university Institutional Review Board (I RB) (Appendix A). Subject’s averaged 221.6 years of age, were 173.8410.452 cm in height, and 67.1312.426 kg in weight.

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41 Time to Stabilization Vertical The group means and standard deviations for vertical TTS can be found in Table 41. The times ranged from 206.71to 385.63-ms during pre-testing and from 200.60to 1175.59-ms during post testing. No significant protocol [F(1,19)=4.96, p=.490] or time [F(1,19)=.000, p=.986] main effects were obser ved. Likewise, no significant protocol by time interaction [F(1,19)= 3.93, p=.538] wa s observed for vertical TTS. Table 4-1. Vertical TTS as determin ed by vertical GRF-Fz (mean SD) Fatigue Protocol Pre-exercise (ms) Post exercise (ms) Combined Protocol (ms) Isokinetic 290.42 42.21 286.15 47.88 288.2944.06 Functional 278.03 52.95 281.85 62.85 279.57758.26 Combined Time 284.2347.68 283.6456.12 Medial/Lateral The group means and standard deviations for medial/lateral TTS can be found in Table 4-2. The times ranged from 53.34to 2232.11-ms during pre-testing and from 997.98to 2219.33-ms during post testing. No significant protocol [F(1,19)=.388, p=.541] or time [F(1,19)=.434, p=.518] main effects were observed. Likewise, no significant protocol by time interac tion [F(1,19)= .287, p=.598] was observed for medial/lateral TTS. Table 4-2. Medial/Lateral TTS as determined by GRF-Mx (mean SD) Fatigue Protocol Pre-exercise (ms) Post exercise (ms) Combined Protocol (ms) Isokinetic 676.57 615.78 350.90 445.51 1491.137493.49 Functional 523.29464.95 533.66 594.12 911.31694.01 Combined Time 912.69710.89 1489.76470.58

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42 Anterior/Posterior The group means and standard deviations for anterior/posterior TTS can be found in Table 4-3. Times ranged from 796.27to 2136.538-ms during pre-testing and from 11.67to 2053.19-ms during post testing. Si gnificant protocol [F(1,19)=8.93, p=.009] and time [F(1,19)=7.72, p=.012] main effects were observed for anterior/posterior TTS. A significantly greater TTS was observed during the pre-test time session (1559.35 344.74 ms) as compared to post-test se ssion (1322.92 427.01 ms) and the functional protocol session (1320.92 417.94 ms) TTS was si gnificantly shorter th an the isokinetic protocol session (1440.20 475.24 ms). However, these significant main effects were not associated with a significant protocol by time interaction [F(1,19)= .001, p=.978]. Table 4-3. Anterior/Posterior TTS as determined by GRF-My (mean SD) Fatigue Protocol Pre-exercise (ms) Post exercise (ms) Combined Protocol (ms) Isokinetic 1444.40323.38 1201.43470.59 1320.92417.94 Functional 1678.97335.21 1201.43470.59 1440.20475.24# Combined Time 1559.35344.74 1201.43476.59* Significantly > Pre-exercise, p<.05 # Significantly > Isokinetic, p<.05 Ground Reaction Forces The group means and standard deviations for peak vertical ground reaction forces can be found in Table 4-4 and 4-5. The gr ound reaction forces were analyzed at two different points in the ground reaction curve, at to e strike (F1) and at th e heel strike (F2). The F1 ground reaction force scores range d from 389.054to 1768.49-N, while the F2 ground reaction force scores ranged from 1308.20to 3748.18-N. A significant time main effect [F(1,19)= 8.64, p=.008] was observed for the ground reaction force at heel strike, as the po st test (2772.57 590.10 N) ground reaction force

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43 was significantly greater than the pre-test (2651.78 588.50 N). However, this was not observed at toe strike, as the time main e ffect was not significant [F(1,19)=1.44, p=.246]. Significant protocol main eff ects were not observed for eith er heel strike [F(1,19)=.80, p=.383] or toe strike [F(1,19)=.46, p=.507]. Likewise, significant protocol by time interactions were not observed for heel strike [F(1,19)=.37, p=.070] or toe strike [F(1,19)=.121, p=.286]. Table 4-4. Toe Strike-F1 as determined by GRF-Fz (mean SD) Fatigue Protocol Pre-exercise (Newtons) Post exercise (Newtons) Combined Protocol (N) Isokinetic 1149.402234.523 1178.551166.41 1163.58207.59 Functional 1103.671321.225 1137.197280.255 1120.43305.05 Combined Time 1125.95286.96 1156.79273.41 Table 4-5. Heel Strike-F2 as determined by GRF-Fz (mean SD) Fatigue Protocol Pre-exercise (Newtons) Post exercise (Newtons) Combined Protocol (N) Isokinetic 2572.752572.042 2783.463623.38 1987.38957.44 Functional 2730.814579.321 2761.685538.683 2746.25566.71 Combined Time 1960.38919.45 2772.57590.10* Significantly > Pre-exercise, p<.05 Joints Kinematics In this study three aspects of joint ki nematics were measured during the dynamic stability protocol. These measurements included a maximum ankle and knee flexion during the jump landing and the maximal knee va lgum that occurred as a result of that landing. Dorsiflexion The group means and standard deviations can be found in Table 4-6. The maximum ankle flexion scores ranged from 53.4 2 to 91.40 at pre-te st and from 55.76

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44 to 94.44 at post test. No significant protocol [F(1,19)= .94, p=.344] or time [F(1,19)=.02, p=.905] main effects were observed. Li kewise, no significant protocol by time interaction [F(1,19)= .06, p=.803] was observed for maximum ankle flexion. Table 4-6. Ankle Flexion (mean SD) Fatigue Protocol Pre-exercise (degrees) Post exercise (degrees) Combined Protocol (degrees) Isokinetic 71.910.2 71.79.5 72.69.2 Functional 69.37.8 69.38.9 69.88.1 Combined Time 71.28.7 71.28.8 Knee Flexion The group means and standard deviations can be found in Table 4-7. The maximum ankle flexion scores ranged from 111.11 to 145.94 at pre-test and from 114.00 to 143.11 at post test No significant protocol [F(1,19)=.67, p=.425] or time [F(1,19)=.58, p=.456] main effects were obser ved. Likewise, no significant protocol by time interaction [F(1,19)= .21, p=.652] was observed for maximum knee flexion. Table 4-7. Knee Flexion (mean SD) Fatigue Protocol Pre-exercise (degrees) Post exercise (degrees) Combine Protocol (degrees) Isokinetic 129.79.3 128.88.0 129.88.9 Functional 128.39.3 128.07.5 128.28.6 Combined Time 129.39.3 128.77.7 Knee Valgum The group means and standard deviations can be found in Table 4-8. The maximum knee valgum scores ranged from -.009cm to .09cm at pre-test and from .008cm to .084cm at post test. No signifi cant protocol [F(1,19)=.07, p=.796] or time

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45 [F(1,19)=.12, p=.737] main effects were obser ved. Likewise, no significant protocol by time interaction [F(1,19)= .79, p=.386] was observed for maximum knee valgum. Table 4-8. Knee Valgum (mean SD) Fatigue Protocol Pre-exerci se (M) Post exercise (M) Combined Protocol (M) Isokinetic 0.030.03 0.030.03 0.030.02 Functional 0.030.02 0.030.02 0.030.02 Combined Time 0.030.02 0.030.02 Correlational Analysis A Pearson product moment correlation was run on the pretest measures of all dependent variables, to determine if inte rdependence existed between the dependent variables. Through the analysis several significa nt correlations were noted. Vertical time to stabilization had significant correlati ons to GRF-F1 (r=.534, p<.001), maximum ankle flexion (r=-.445, p=.004), and maximum knee flexion (r=-.667, p<.001). The other TTS measures, medial/lateral, and anterior/posterior only had a significant correlation with GRF-F2 (r=-.775, p=.001) and (r=.401, p=.011). In addition to the significant correlation that GRF-F1 had with vertical TTS, a signifi cant correlation was also noted with maximal knee flexion (r=-.385, p=.015). Maximal ankle fl exion also had an additional significant correlation with maximal knee flexion (r=.533, p=.001). There were no significant correlations found for knee valgum scores. A complete table of the Pearson product moment correlation coefficients can be seen in Table 4-9.

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46 Table 4-9. Pearson Product Moment Correlation (r and significance) Pearson product moment correlation coefficients Vertical Med/LatAnt/PosGRF-F1GRF-F2Ankle Knee Valgum Vertical r Sig. 1 .173 .284 .145 .373 .534* .001 .158 .336 -.445* .004 -.667* .004 -.208 .198 Med/Lat r Sig. .173 .284 1 -.267 .095 .116 .483 -.775* .001 .182 .262 .011 .946 -.027 .866 Ant/Pos r Sig .145 .373 -.267 .095 1 .128 .438 .401* .011 -.179 .268 -.309 .053 .131 .420 GRF-F1 r Sig .534* .001 .116 .483 .128 .438 1 .222 .175 -.230 .159 -.385* .015 -.137 .405 GRF-F2 r Sig .158 .336 -.775* .001 .401* .011 .222 .175 1 -.201 .221 -.297 .066 -.104 .528 Ankle r Sig -.445* .004 .182 .262 -.179 .268 -.230 .159 -.201 .221 1 .533* .001 .077 .637 Knee r Sig -.667* .004 .011 .946 -.309 .053 -.385* .015 -.297 .066 .533* .001 1 -.031 .852 Valgum r Sig -.208 .198 -.027 .866 .131 .420 -.137 .405 -.104 .528 .077 .637 -.031 .852 1 Correlation is significant at the .05 level (2-tailed)

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47 CHAPTER 5 DISCUSSION The purpose of this study was to comp are the effects of isokinetically and functionally induced fatigue on time to stabil ization (TTS), peak vertical ground reaction forces and joint kinematics (i.e., ankle and knee flexion and knee valgum) during a single-leg landing stabilization test. Three hypotheses were examined and are discussed below. The first hypothesis stated that ther e would be significant increases in time to stabilization, peak vertical ground reaction fo rces, and joint kinematics in the post test measures as compared to the pretest meas ures. The second hypothesis stated that a greater change in the dependent variables w ould be noted following functional fatigue as compared to isokinetic fatigue. The results of this study failed to support either of these hypotheses. The third hypothesi s stated that there would be a high correlation between peak vertical ground reaction forces and time to stabilization when assessed in an unfatigued state. In general, there was a lo w to moderate relations hip to support the third hypothesis. Fatigue The primary purpose of this study was do de termine if functionally induced fatigue would have a greater effect on TTS and join t kinematics as compared to isokinetically induced fatigue. However, no differences were observed when comparing the two fatigue protocols. It is di fficult to make comparisons betw een the two types of exercise, as neither protocol had an eff ect on these variables. This conflicts with the results of previous studies assessing the influen ce of fatigue on neuromuscular control.9,16,17,19

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48 Johnston et al.9 and Douex et al.19 reported that both isokine tic and functional fatigue protocols respectively, signifi cantly increased postural sw ay as subjects stood on an unstable platform. Likewise, Yaggie and McGregor16 and Joyce et al.17 induced fatigue in the dorsi and plantar flexors using an isokinetic protocol an d observed a significant increase in postural sway during a unil ateral balance task. Yaggie and McGregor16 observed this difference with an eccentric /concentric mode at 60 per second while additionally running the prot ocol on inversion/eversion motions. Joyce et al.17 utilized the same isokinetic fatigue protocol that wa s used in this stud y, but conducted that protocol in a prone position. It is importan t to note that none of the above studies used TTS as a measure of neuromuscular control or stability. Thus, it is difficult to make comparisons with our study. It is possible that we might have observed changes has similar testing protocols been used. It is possible that the isokinetic and f unctional exercise prot ocols used in the present investigation did not sufficiently fatigue the musculature of the lower leg. If they had been sufficient, differences in TTS, GRF, or joint kinematics would be expected. No one definition of fatigue exists in the literature, as fatigue can occur at numerous points in the neuromuscular pathway. For the present i nvestigation, isokinetic fatigue was defined as the point at which a subject could not produce 50% of their respective plantar and dorsiflexion peak torque at the respectiv e speeds of 30 and 1 20 per second in a concentric/concentric mode. This specifi c protocol has been used previously, by Johnston et al.9 and Joyce et al.17 who as stated earlier determ ined that isokinetic fatigue protocols effect postural swa y. The increased postural sw ay observed in those studies suggests that the lower leg musculature was su fficiently fatigued. Thus, changes in our

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49 dependent measures would be expected as we ll. These isokinetic protocols directly fatigue the plantar flexors, which are the ma in stabilizing muscles for balancing over an extended period of time.3,4,25 However, during the time to stabilization, the single leghop protocol vertical TTS scores averaged le ss than .05-sec, while the medial/lateral and anterior/posterior scores we re typically less than 3-sec. When landing from a forward jump, momentum brings the center of gravit y forward over the sta tionary foot. Thus, dorsiflexion occurs at the ankl e or anterior sway. When th is occurs, the plantar flexors are stimulated via the stretch reflex to retu rn the body to a stable position. The triceps surae muscle group, reported as the main stab ilizers for balance, woul d then play a vital role in the initial phase of landing that th e single leg hop protocol reproduces. If this theory is correct, then an isokinetic fatigue protocol should have an effect on TTS scores and reinforces the assumption that the isokine tic fatigue protocol used was not sufficient to fatigue the lower leg musculature. Douex et al.19 used a functional protocol, fatig uing the subject anaerobically through a series of 40-yard sprints. We defi ned functional fatigue as the point at which a subject could not complete the exercise protoc ol in less than 150% of their initial time. Muscular fatigue induced in similarly in isoki netic protocols have been shown to last up to 90 seconds post fatigue.11 While the functional fatigue protocol has not been used previously in the literature, there were anec dotal reports of delayed onset muscle soreness following testing. Unlike the isokinetic protocol this type of exercise involved knee, hip, and upper extremity musculature. This prot ocol was designed to incorporate, various aspects of athletic competition, including ag ility, quick explosive movements, muscular endurance, and aerobic capacity. Agility a nd balance in the two leg hop sequence and

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50 agility drill. Quick explosive movement s in the plyometric box jump. Muscular endurance and aerobic capacity of the lower extremity musculature and the cardiopulmonary system were respectively st ressed through the series of side-to-side bounds, mini-tramp jumps and co-contracti on arcs. Aerobic capacity was also incorporated in the overall time to completion of the fatigue protocol. On average time to complete one circuit was approximately 5 minutes, with most subjects performing 3-4 circuits before fatigue. It is possible that the increases in time to perform the protocol were due to reduced effort as opposed to actua l fatigue. However, it is possible that our functional fatigue protocol wa s not comprehensive enough to fatigue the lower extremity musculature or not specific enough to fatigue the necessary lower extremity musculature to indicate a difference in TTS scores. Similarly, the opposite could be true, the functional fatigue protocol could have been too effective. Decreasing the subjects neuromuscular control to a level where they could not complete the jump protocol until after fatigue had decreased. Jump Landing Protocol Several jump-landing protocols have been used in previous studies to measure postural sway. Forward and late ral step down tests as well as single leg hop tests have all indicated significant effects of fatigue on stabilization time12,18,52. It is possible that our failure to observe changes following fatigue was due to trial mo rtality and difficulty during the performance of the jump landing test s. It could be reasoned that the jump protocol may be too difficult or not specific enough to de termine differences between healthy subjects. Few studies have used TTS as a measure of stability or neuromuscular control; however, only one of these studies has examined the effects of fatigue. Previous studies

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51 have compared healt hy and injured subjects12,52. The results from these studies suggest that subjects with functionally unstable ankles52 and subjects with ACL deficiencies12 experience longer times to st abilization than healthy subjects. Maggio et al.18 examined the effects of evertor muscle fatigue on dynami c stabilization time. In that study, healthy and functionally unstable ankles were asse ssed during a forward and lateral step down test protocol. The results indicated a si gnificant difference in FUA subjects, but no difference in healthy subjects. We only used he althy subjects in the present investigation. Thus, our results are in agreement with thos e involving the healthy subjects assessed in the above-mentioned study. Due to the trial mortality and the subjects’ inability to land in a balanced state, a greater variation in the time to stabilization scores was s een. These variations would directly effect the medial/later al and anterior/posterior TTS sc ores as the subjects tried to regain balance after landi ng. Concurrent with the results of Maggio et al.18, data from this study illustrate a performance improveme nt in time to stabilization scores post fatigue in healthy subjects. Also noted were the high scores on both TTS measures during the functional fatigue pr otocol, despite the lack of significance found. These variations in landing as a result of the compli cated landing task may also indirectly effect the vertical TTS scores. This illustrates th e minor trend occurring towards an interaction for vertical time to stabilization as well as the trend towards a main effect between fatigue protocols. Despite the variations, which would have been noted across the pre and posttest trials, the trial mortality, might have affected the posttest sessions more severely. While the post test trials were initiated 30 seconds after completion of the respective fatigue

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52 protocols, the completion of the post test data collection took much longer than anticipated. This delay in data collecti on might have allowed some degree, if not complete, recovery of the fatigued muscles. This recovery woul d reduce deficits in proprioceptive awareness and muscular for ce, potentially incr easing the subjects’ neuromuscular control for the post-test sessi ons. The delay in data collection may also explain why some TTS scores we re lower during post fatigue te sting respective to the pre fatigue scores. This trend was concurrent with Maggio et al.18 who also indicated that the scores of healthy subjects tended to improve dur ing the post-test trials. If due to the trial mortality and delay in colle ction, subjects’ propriocepti ve feedback and muscular strength returned to normal, then the lower post-test scores can be explained by a learning effect. Validity of Measure It is also possible that TTS is not the best test to meas ure the effects of fatigue on neuromuscular control. Reliable methods commonly reported in th e literature include single-leg-stance both on a force plate and unstable platform and the star excursion balance test.9,13,16 These measures may be more sensit ive to variations in ground reaction forces or center of pressure changes resulti ng from lower extremity muscle fatigue. This rationale forces a look at the assumption that th e subject effort would be maximal. If subject effort was not maximal during the fatigue protocols, then the post-test scores are not true indicators of how fatigue would affect the said dependent variables. Furthermore, if subject effort was not full dur ing the testing protocol then the scores of the dependent variables are not accurate or tr ue representations of the changes to them due to fatigue.

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53 Ground Reaction Forces This study did find significance for the peak vertical ground reaction forces at the heel strike (F2). This finding indicates that as fatigue of the lowe r extremity musculature increases, the body’s ability to absorb the s hock of a landing decrease s, despite the lack of significance found in the other measures taken. This is due to the triceps surae muscle groups losing the ability to eccentrically de celerate the body from a jump landing. This inability to control decelerat ion creates a more unimodal or flat-foot landing style which could potentially increases the chances of a nkle injury. These findings are concurrent with those of 10,24,55 whose studies also indicated an in crease in GRFs due to fatigue. In Figure 5-1, the trend for the peak vertical ground reaction forces at point F2 can be seen. These charts illustrate that a trend did occur toward an interaction of test and protocol at the F2 collection point. Both these points (F1, F2) in the ground reaction force history curve were also moderately correlated to the vertical TTS and medial /lateral as well as anterior/posterior TTS scores respectively. 0 1000 2000 3000 4000 5000 6000 Pre to PostNewtons functional isokinetic Figure 5-1. Peak vertical GR F at heel strike (F2).

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54 Joint Kinematics In this study, aspects of joint kine matics were measured during the dynamic stability protocol: including maximum ankl e and knee flexion during the jump landing and the maximal knee valgum that occurred as a result of that landing. There were no significant differences found in any kinematic measurement as a result of this study. However, a moderate negative correlati on between maximal dorsi and knee flexion was found with vertical time to stabilization. This indicate s that the less flexion of the said joint angle would indicate a greater vertical TTS score. Correlation The results of this study indicate that there is a m oderate relationship between vertical TTS and GRF-F1, as well as for an terior/posterior TTS and GRF-F2. A high correlation was found between medial/lateral TTS and GRF-F2. These results help illustrate that the measure of time to stabilization is in part determined by the force by which a subject lands for the jump protocol. Th is analysis also indicates that the higher a person’s force at toe touch, the higher their ver tical time to stabilization will be; while the force at heel strike is positively correlated to anterior/posterior TTS, the less force at heel strike the smaller the anterior/posterior TTS score will be. Force at heel strike was negatively correlated to medial/lateral TTS, indi cating that the less force at heel strike, the greater the medial/lateral TTS score will increase. Indications The results of this study i ndicate that there is no diffe rence between the effects of an isokinetic and a functional fatigue protoc ol of the lower leg and that there was no difference between the TTS, GRF, and joint kine matic scores prior to and after fatigue. These finding are contrary to previous studi es that indicated that both isokinetic and

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55 functional fatigue protocols have si gnificantly increased postural sway.9,16-19 This study may however indicate that an is okinetic fatigue protocol coul d potentially be a valid and acceptable method to study the effects of fatigue This would allow for faster, safer and more reproducible tes ting of subjects in an effort to better understand the effects of fatigue on neuromuscular control. However, until a definitive and direct answ er of whether or not an isokinetic or functional fatigue protocol is the best means to study fatigue’s effect on neuromuscular control and postural sway can be made, compar ative studies should be the basis for future research. It is also import ant that athletic trainers, co aches, therapists, and physicians continue to train their athl etes in ways that will incr ease their proprioception and minimize any loss of neuromuscular control due to the fatigue of athletic competition until the exact cause of proprioceptive deficits and loss of neuromuscular control can be established. Conclusions The following conclusions are made as a result of this study: There was no difference in time to stabilizat ion scores prior to and after an isokinetic and functional fatigue protocol of the lower extremity musculature. There was no difference between the effects of an isokinetic fatigue protocol on TTS, GRF and joint kinematics as compared to a functional fatigue protocol. There was a moderate correlation between ve rtical time to stabilization and maximal ankle and knee flexion. There was also a high correlation between GRF-F2 and medial/lateral time to stabilization. Summary The results of this study i ndicate that there is no diffe rence between the effects of an isokinetic and a functional fatigue protoc ol on TTS, GRF, and joint kinematics. The

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56 results also indicate that there is a small to moderate correlation be tween several of the dependent variables. While muscle fatigue has been shown to increase postural sway and vertical GRF in several studies, by incorporating isokineti c and or functional fa tigue protocols, the results of this study indicate there no rela tionship between increases in fatigue and increases in time to stabilizat ion. However, the results of this study do indicate that fatigue does increase the vertical GRF seen at heel strike. This increase has been associated with an increased latency pe riod and altered joint kinematics in jump landing.10,24,55 Two possible indicators of increases incidence of injury at the ankle. These results benefit researchers indicating that an isokinetic fa tigue protocol is a reliable method of mimicking the fatigue that takes place duri ng athletic activity. Until a definitive answer to the question of why the ankle is the most commonly injured structure in the body, and fatigue pl ays a role, athletic trainers, therapists, physicians, and coaches should encourage athletes to focus on improving their proprioceptive awareness and proper tec hnique in landing from jumps. Improving proprioception and learning pr oper landing techniques may help in reducing an athlete’s chances of suffering an ankle injury. Implications for Future Research This study has generated several new ques tions in which future researchers can explore. This study tested healthy subj ects who had no previous history of lower extremity injury. Future research should examine subjects with previous injuries, including those with functiona l and anatomical ankle instability. The current study used a fatigue protocol that used 50% of peak to rque and initial time as the standard for fatigue. Future research should be conducte d with various levels of fatigue as a

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57 percentage of peak torque for an isokinet ic protocol and initial time for a functional fatigue protocol. Future research should al so examine further comparative studies of isokinetic and functional fatigue protocols measuring their ef fects with more tested and reliable measures of postural sway. In addition, future research should look to determine the learning effect associated with the time to stabil ization single leg hop pr otocol, it’s reliability and validity and the various methods of calculating it. Comparis ons of a control and treatment group would add to the general body of knowledge and i ndicate the amount of practice needed to minimize the learning effect for this protocol. If valid and reliable, future studies should examine the differences in time to stabilization between males and females. Other research endeavors should explore the effect of various sensory deprivation on time to stabilization and more importantly the change s in postural sway and time to stabilization over the course of actual athletic practice a nd games in varying sports. Also, future research should include a prospective study to determine if time to stabilization is a predictor of the incidence of a nkle injuries in the sports wh ere jump landing is prevalent, such as basketball, soccer, and volleyball.

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58 APPENDIX A LETTER OF INFORMED CONSENT Informed Consent Agreement Project Title: Effects of isoki netic vs. functional fatigue protocol of the lower extremity on time to stabilization and peak vertical ground reaction forces. Investigators: Erik A Wikstrom,ATC, Gradua te Student, Department of Exercise and Sport Sciences & Michael E. Powers, Ph D., ATC, CSCS, Assisstant Professor, Department of Exercise and Sport Sciences. Purpose of the study: The purpose of this study is to compare and corr elate the effects of two different methods of tiring out the lo wer leg, by measuring the required time to regain your balance and how much force you produce from landing during a single-leghop balance test. This study will also examine the amount of flexion or bend that occurs in the ankle and knee from the fatigued la nding during the single-l eg-hop balance test. Please read this consent carefully before you decide to participate in this study. What will you do in this study? Upon reporting to the Athletic Training/Spor ts Medicine Research Laboratory (105D FLG), you will be asked to complete the medical history form to determine if you are eligible to participate in the study. If eligible, your maximu m vertical leap (how high you can jump) will be determined. To do this, we will first measure how high you can reach while standing. You will then be asked to jump as high as possible and touch markers supported on a stand. Based on the number of markers you touch, the height of your jump is determined. We will have you do this two more times to asure that we get an accurate measure. Immediately following the jump test, we will place reflective markers on the outside of your ankles, knees, hips, and shoulders using tape. We will then measure how long it takes you to balance afte r jumping onto a platform. You will be asked to jump so that you reach a height equi valent to half of your maximum jump height and land on a platform 28” away. After you land on the platform you will be asked to balance yourself on one leg while your hands remain on your hips for a period of 20 seconds. You will be video taped while you do this. The video tape and the reflective markers will allow us to determine how well you balance. After the 20-second period you will be asked to return to the starting pos tion and repeat the measurement. This will be done one more time for a to tal of three trials. After the balance measurements are completed, we will attempt to fatigue (tire ou t) your lower leg muscles using one of two methods. Which method you do first will be randomly determined by a coin toss.

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59 One of the fatigue protocols will require you to sit in a chair in a machine that will fatigue your muscles by providing maximum resi stance at a set speed of movement as you bring and point the foot and toes upward a nd then point the foot and toes downward. You will warm up and determine your stronges t movement and after a minute of rest proceed with the test by continuously repe ated the above motions of the ankle until fatigue, which will be 50% of your strongest movement as determined by the computer on the machine. The other fatigue protocol will requrie you to complete a series of timed sprinting, cutting and jumping stations. You will first warm up and received instructions. After a minute of rest you will start by runni ng through a timing marker and then complete the stations in order until the series is complete. Afte r each series of stations you must run back through the timing marker. You will be asked to continue performing the stations until a series takes you 1 times as long as the first se ries (50% longer than the first series). The stations in each series will consist of the following; Agility drill A series of forward sprints, dia gonal back-pedaling, and side stepping within a 12’ x 12’ area. (3 times) Box jumping A drill that mimics the rapid jumping and landing that would be experienced in athletic competiti on. This drill is a series of 3 boxes of 24” in height 18” apart. You will jump onto the first box, st abilize and jump down, immediately jumping back up onto the second box, stabilize and repeat onto the third box. (3 times) Two-legged hop sequence A series of markers spaced over a ten foot distance, must be jumped onto and immediately left for the next marker. You need to jump and land using both feet for each marker. (3 times) Side-to-side bounds An area 5’ wide in which you will jump sideways from a center marker to the one side and back to th e center to the opposite side. (30 times) Mini-tramp You will be ased to jump onto a mi ni-trampoline, stabilize and jump off onto the floor on the opposite side. (30 times) Resistance arc You will be asked to resist the te nsion of an elastic cord as you side shuffle around semi circle. (10 times) Immediatley after you are done with the fatigue protocol you will be asked to return to the laboratory and complete an other balance test identical to the one completed before the fatigue protocol. Once this is completed the session will be over. You will be asked to return to the laboratory 1 week later to repeat the entire protocol, however, you will perform the other fatigue protocol (the one you did not perform on the first day). Time requried: Two sessions requiring approximately 45 minutes each. Risks: As with any type of exercise, there is a slight risk of musculoskeletal injury such as a sprain or a muscle pull. A certified athletic trainer will be present to evaluate and treat any such injuries shou ld they occur.

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60 Benefits/Compensation: There are no direct benef its to you for participating. Confidentiality: Data will be kept confidential to the extent provided by the law. Your information will be assigned a code number. The list connecti ng your name to this number will be kept in a locked file. When the study is completed and the data have been analyzed, the list will be destroyed. Your name will not be used in any report. Voluntary Participation: Your participation is complete ly voluntary. There is no pe nalty for not participating. Right to withdraw from the study: You have the right to withdraw from the study at anytime without penalty. Who to contact if you have questions about the study: Erik A Wikstrom, BS, ATC/L Mike Powers, Ph.D., ATC/L, University of Florida University of Florida Department of Exercise and Sport Sciences Department of Exercise and Sport Sciences Graduate Assistant Athletic Trainer 148 Florida Gym 2777 SW Archer Road Apt. R-85 PO Box 118205 Gainesville, FL 32608 Gainesville, FL 32611-8205 372-5592(home) (352) 392-0584, ext. 1332 Fax: (352) 392-5262 Fax: (352) 392-5262 E-mail: gatoratc@hotmail.com E-mail: mpowers@hhp.ufl.edu Who to contact about your rights in the study: UFIRB Office Box 112250, University of Florida Gainesville FL 32611-2250 (352) 392-0433. Agreement: I have read the procedure described above. I voluntarily agree to participate in the procedure and I have received a copy of this description. Participant:______________________________ Date:__________ Principal Investigat or:___________________________ Date:__________

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61 APPENDIX B MEDICAL ELIGIBILI TY QUESTIONAIRE 1. Name_______________________________________________ 2. Age______________________ 3. Height / Weight__________________________ 4. What leg would you kick a soccer ball with? Left________ Right_______ 5. Have you had a lower extremity inju ry within the past six months? Yes________ No_________ 6. Have you been diagnosed with a conc ussion within the past six months? Yes________ No_________ 7. Have you been diagnosed with an equilibrium disorder? Yes________ No_________ 8. Do you have a diagnosed disorder th at affects neuromuscular control? Yes________ No_________ 9. How often do you exercise? 0-2 times a week_____ 2-4 times a week_____ 4+ times a week______

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62 APPENDIX C DATA COLLECTION FORMS Subject #________________________ Stance Leg___________________ Maximal Vertical Leap_____________ Jump Height (50%max)____________ Isokinetic Protocol PRE-TEST: Trial 1 Trial 2 Trial 3 Time to stabilization _______ _______ _______ GRF-F1 _______ _______ _______ GRF-F2 _______ _______ _______ Ankle Flexion _______ _______ _______ Knee Flexion _______ _______ _______ Knee Valgus/Verus _______ _______ _______ Fatigue Protocol Peak Torque PF_________ DF__________ Fatigue PF________ DF________ Actual Percentage PF_________ DF__________ POST-TEST : Trial 1 Trial 2 Trial 3 Time to stabilization _______ _______ _______ GRF-F1 _______ _______ _______ GRF-F2 _______ _______ _______ Ankle Flexion _______ _______ _______ Knee Flexion _______ _______ _______ Knee Valgus/Verus _______ _______ _______

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63 Subject #________________________ Stance Leg___________________ Maximal Vertical Leap_____________ Jump Height (50%max)____________ Functional Protocol PRE-TEST: Trial 1 Trial 2 Trial 3 Time to stabilization _______ _______ _______ GRF-F1 _______ _______ _______ GRF-F2 _______ _______ _______ Ankle Flexion _______ _______ _______ Knee Flexion _______ _______ _______ Knee Valgus/Verus _______ _______ _______ Fatigue Protocol Initial Time PF_________ DF__________ Fatigue PF_______ DF________ Actual Percentage PF_________ DF__________ POST-TEST : Trial 1 Trial 2 Trial 3 Time to stabilization _______ _______ _______ GRF-F1 _______ _______ _______ GRF-F2 _______ _______ _______ Ankle Flexion _______ _______ _______ Knee Flexion _______ _______ _______ Knee Valgus/Verus _______ _______ _______

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64 APPENDIX D ANOVA TABLES Tests of within-subjects effects Table D-1. Vertical TTS ANOVA table Source Sum of SquaresDfMean SquareF Sig. Protocol 1371.747 1 1371.747 .496 .490 Error(protocol) 52545.726 192765.565 Time 41138.323 1 41138.323 2.239 .151 Error(time) 29418.152 191548.324 Protocol*Time 337.779 1 337.779 .393 .538 Error(protocol*time) 16342.684 19860.141 Table D-2. Medial/Lat eral TTS ANOVA table Source Sum of SquaresDfMean SquareF Sig. Protocol 74416.930 1 74416.930 .388.541 Error(protocol) 3644487.244 19191815.118 Time 109031.775 1 109031.775 .434.518 Error(time) 4776494.299 19251394.437 Protocol*Time 23209.609 1 23209.609 .287.598 Error(protocol*time) 154370.268 1980756.330 Table D-3. Anterior/Pos terior TTS ANOVA table Source Sum of SquaresDfMean SquareF Sig. Protocol 1117970.407 1 111970.407 8.529 .009* Error(protocol) 2490392.677 19131073.299 Time 1162682.933 1 1162682.9337.725 .012* Error(time) 2859804.258 19150516.014 Protocol*Time 68.859 1 68.859 .001 .978 Error(protocol*time) 1747346.945 1991965.629 Indicates significance; p<.05

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65 Table D-4. GRF-F1 ANOVA table Source Sum of SquaresDfMean SquareF Sig. Protocol 21760.031 1 21760.031 .459 .507 Error(protocol) 805763.143 1747397.832 Time 19669.628 1 19669.628 1.441 .246 Error(time) 232056.582 1713650.387 Protocol*Time 13237.474 1 13237.474 1.211 .286 Error(protocol*time) 185829.458 1710931.145 Table D-5. GRF-F2 ANOVA table Source Sum of SquaresDfMean SquareF Sig. Protocol 92866.586 1 92866.586 .797 .383 Error(protocol) 2213852.009 19116518.527 Time 291813.119 1 291813.119 8.644 .008* Error(time) 641402.224 1933758.012 Protocol*Time 161712.712 1 161712.712 3.673 .070 Error(protocol*time) 836419.613 1944022.085 Indicates significance; p<.05 Table D-6. Ankle Flexion ANOVA table Source Sum of SquaresDfMean SquareF Sig. Protocol 125.572 1 125.572 .940.344 Error(protocol) 2537.431 19133.549 Time .129 1 .129 .015.905 Error(time) 167.522 198.817 Protocol*Time .409 1 .409 .064.803 Error(protocol*time) 121.710 196.406 Table D-7. Knee Flexion ANOVA table Source Sum of SquaresDfMean SquareF Sig. Protocol 23.671 1 23.671 .666.425 Error(protocol) 675.398 1935.547 Time 6.173 1 6.173 .580.456 Error(time) 202.287 1910.647 Protocol*Time 1.710 1 1.710 .209.652 Error(protocol*time) 155.197 198.168

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66 Table D-8. Knee Val gum ANOVA table Source Sum of SquaresDfMean SquareF Sig. Protocol 4.033E-05 1 4.033E-05 .069.796 Error(protocol) 1.116E-02 195.873E-04 Time 1.296E-05 1 1.296E-05 .116.737 Error(time) 2.127E-03 191.119E-05 Protocol*Time 9.288E-05 1 9.288E-05 .788.386 Error(protocol*time) 2.239E-03 191.178E-04

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67 APPENDIX E RAW DATA TABLES Table E-1. Subject Demographics. Subject Sex Stance Leg Height Weight Max Vertical Jump Height Peak Torque PF Peak Torque DF Intial Time Units Body Wieght (cm) (kg) (cm) (cm) (newtons (newtons (min-sec) (volts) 1 female left 170.18 61.36 31.75 15.88 593 103 4:38 1.658 2 female left 172.72 65.90 33.02 16.51 389 215 4:30 1.717 3 male left 187.96 75.00 45.72 22.86 430 260 5;13 2.024 4 female left 170.18 59.09 20.32 10.16 472 72 3:44 1.543 5 male left 177.80 59.09 50.80 25.40 453 319 4:00 1.466 6 male left 182.42 91.81 50.80 25.40 824 438 4:20 2.398 7 male left 182.88 74.09 43.18 21.59 640 434 3:53 1.939 8 female left 167.64 73.63 25.40 12.70 606 243 4:36 1.943 9 male left 172.72 79.54 35.56 17.78 807 294 4:00 2.000 10 female left 177.80 75.00 30.48 15.24 724 208 4:45 2.099 11 male left 167.64 54.54 53.34 26.67 617 110 3:30 1.317 12 female left 177.80 72.72 21.59 10.80 497 222 4:31 1.895 13 male left 182.88 70.45 43.18 21.59 496 231 5:03 1.854 14 female left 170.18 63.63 29.21 14.61 975 135 5:00 1.766 15 female left 147.32 45.45 34.29 17.15 360 58 3:42 1.325 16 male left 190.50 88.63 46.99 23.50 442 140 4;30 2.29 17 female left 157.48 50.90 36.83 18.42 335 85 3:00 1.469 18 female left 185.42 70.45 25.40 12.70 419 92 4:04 1.798 19 female left 165.10 47.72 19.05 9.53 318 56 6:11 1.398 20 female left 170.18 63.63 27.94 13.97 412 64 4:45 1.717 Mean 173.84067.13235.243 17.621540.450 188.950 0.181 1.781 STD 10.452 12.46210.720 5.360 179.668 118.130 0.030 0.305

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68 Isokinetic Protocol Data Table E-2. Pretest Isokinetic Data. Subject Ave-VertTTS AveMed/LatTTS AveAnt/PosTTS AveGRF-F1 AveGRF-F2 Ave-AnkleAve-KneeF Ave-KneeV 1 385.633 205.041 12.780 1196.8252420.57553.420 117.779 -0.005 2 305.617 815.163 10.558 1086.6542242.27673.726 137.275 0.020 3 284.501 31.117 443.978 1353.1523534.04262.067 128.099 0.051 4 304.505 78.905 204.485 2264.69278.130 134.345 -0.009 5 255.051 1535.107 599.564 1309.5693229.17071.431 120.652 0.068 6 361.739 397.857 752.373 1459.0593670.96573.708 114.982 0.016 7 283.390 1364.162 74.459 1327.7492334.91970.296 119.922 0.023 8 276.722 1526.416 25.561 1053.9792346.15291.401 137.436 0.050 9 238.381 643.462 210.597 1505.6303364.18478.698 138.865 0.002 10 267.831 2008.735 370.074 1082.5122643.38866.220 136.940 -0.009 11 312.285 1211.909 640.683 1060.8612398.78463.890 119.608 0.090 12 312.285 87.795 472.872 824.468 2609.91966.129 136.575 0.033 13 351.737 21.671 1775.355 1215.1242858.84858.991 120.478 0.012 14 265.053 877.953 10.558 1269.7712026.38481.686 131.165 0.066 15 252.828 436.198 7.779 998.953 1759.75470.040 135.908 0.044 16 335.623 1208.019 470.761 1355.9993059.61961.809 120.026 0.037 17 262.275 11.113 1353.604 1181.8912327.59962.474 120.453 0.040 18 241.159 36.674 28.339 517.830 2675.81089.628 141.883 0.033 19 248.383 686.804 17.781 829.357 1308.20677.920 135.318 0.024 20 263.386 347.292 964.082 1209.2512379.74486.646 145.936 0.049

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69 Table E-3. Posttest Isokinetic Data. Subject Ave-VerrtTTS AveMed/LatTTS AveAnt/PosTTS AveGRF-F1 AveGRF-F2 Ave-Ankle Ave-KneeF Ave-KneeV 1 272.832 99.464 606.788 963.901 2187.47657.280 119.306 -0.008 2 322.287 371.182 7.224 1104.2532419.85468.562 131.715 -0.007 3 262.830 17.781 7.224 1352.4133748.17870.768 129.609 0.037 4 380.076 1503.634 741.815 2591.46173.817 130.210 -0.004 5 352.570 442.311 6.112 1217.4553682.61567.285 118.652 0.043 6 368.407 55.011 1385.833 1500.2963712.12976.943 114.005 0.018 7 277.278 792.381 766.264 1210.5462464.04075.098 125.190 0.019 8 287.835 58.901 29.450 1107.3632475.97990.148 133.226 0.047 9 233.380 1047.432 1196.906 1307.4713292.26480.540 138.799 0.008 10 253.384 266.720 54.455 1125.0722773.72666.095 138.202 -0.002 11 263.386 20.004 26.672 1138.3292864.93064.069 118.787 0.072 12 261.163 1137.450 1007.424 962.746 3452.65167.414 132.692 0.043 13 295.615 13.883 656.798 1507.2153592.22360.882 124.143 0.014 14 297.837 53.344 11.669 1216.4532090.32578.476 130.427 0.084 15 333.400 47.232 409.526 1037.8681885.09266.288 132.220 0.041 16 297.282 613.456 492.321 1145.5313040.01765.149 119.426 0.037 17 235.047 11.113 983.530 1208.8292726.98858.354 121.955 0.014 18 200.596 30.006 19.448 2587.51194.440 143.115 0.042 19 225.601 383.410 13.336 859.659 1500.34274.305 137.629 0.021 20 302.283 53.344 11.113 1248.5152581.46877.931 137.376 0.055

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70 Functional Protocol Data Table E-4. Pretest Functional Data. Subject AveVertTTS AveMed/Lat TTS AveAnt/Pos TTS Ave GRF-F1 Ave GRF-F2 Ave-AnkleAve-KneeF Ave-KneeV 1 309.506 1036.674 1046.876 1141.1162664.65561.981 129.317 0.056 2 322.287 135.583 190.038 1523.9352913.46681.230 126.765 0.004 3 310.618 501.767 33.896 1034.4373592.01465.190 124.388 0.051 4 211.709 16.670 589.562 389.054 2348.94487.639 128.753 0.042 5 320.620 345.625 953.524 1268.8223275.86963.958 128.112 0.027 6 371.185 503.990 45.009 1318.6803737.40763.673 111.110 0.027 7 357.849 974.639 31.673 1379.0983279.76168.593 118.702 0.013 8 258.941 734.591 23.338 925.211 2094.03972.705 137.854 0.018 9 247.827 192.261 307.839 1432.6483455.75776.160 133.928 0.039 10 248.383 53.900 9.446 1037.2023286.09471.471 133.180 0.041 11 318.953 1536.418 772.377 1032.5562544.80066.229 111.482 0.053 12 270.610 703.474 57.789 1096.3762571.18476.160 136.207 0.001 13 280.612 1180.792 419.528 1258.7542974.85275.663 123.255 0.012 14 225.601 78.349 1193.572 1313.0192176.46471.891 141.148 0.055 15 206.708 127.248 340.068 826.179 1893.39670.040 135.908 0.042 16 362.850 260.052 71.681 1768.4912847.23356.513 113.272 0.005 17 226.712 870.730 741.259 919.924 2639.91360.717 121.356 0.020 18 240.604 36.674 28.339 501.276 2424.93761.293 129.721 0.024 19 209.486 66.124 14.447 807.485 1465.02774.818 141.765 0.006 20 259.496 1110.222 6.112 1099.1602430.46259.412 139.816 0.026

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71 Table E-5. Posttest Functional Data. Subject AveVert-TTS AveMed/LatTTS AveAnt/PosTTS Ave GRF-F1 Ave GRF-F2 Ave-Ankle Ave-KneeF Ave-KneeV 1 292.281 35.563 48.343 1013.7382387.15156.848 125.968 0.031 2 293.948 21.671 11.113 1339.6263317.05577.957 124.459 0.013 3 253.940 57.234 17.226 980.144 3533.22664.820 130.208 0.045 4 247.272 485.653 740.704 1715.8992650.02290.775 138.095 0.039 5 342.291 25.005 632.904 930.004 3603.54064.661 129.306 0.042 6 335.067 667.911 45.009 1450.3963462.41865.796 114.135 0.023 7 489.542 402.858 139.472 1188.2962930.46164.842 119.399 0.025 8 258.385 1308.039 47.787 512.813 2294.88281.106 142.812 0.037 9 261.163 245.049 921.851 1574.3363572.76079.419 131.345 0.012 10 281.723 1124.669 176.702 928.309 3098.84573.942 131.713 0.027 11 1175.591 804.050 583.450 900.689 2840.39864.420 115.111 0.054 12 245.049 18.893 24.449 1198.3302068.20974.819 132.742 0.049 13 228.379 38.341 804.328 1138.2502879.32178.875 120.075 0.016 14 232.269 393.412 475.095 1184.1642199.68870.651 136.546 0.047 15 230.602 25.005 100.576 1006.9312017.75466.288 132.220 0.039 16 373.408 1561.979 35.563 1622.3313135.60259.549 122.086 -0.002 17 1149.474 821.275 8.335 1002.2192474.58160.538 121.455 0.016 18 220.600 273.388 20.560 928.113 2585.36663.331 128.793 0.026 19 296.726 251.161 242.271 1074.8522032.64272.195 136.293 -0.001 20 252.273 2112.089 19.448 1054.5082149.78355.760 128.013 0.053

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74 26. Dufek J, Bates B. Biomechanical factor s associated with in jury during landing in jump sports. Sports Medicine 1991; 12(5): 326-337. 27. Beynon B, Dalene M, Alosa D. Predicti ve factors for lateral ankle sprains: A literature review. Journal of Athletic Training 2002; 37(4): 376-380. 28. Harter R. Clinical rationale for closed kinetic chain activities in functional testing and rehabilitation of ankle pathologies. Journal of Sport Rehabilitation 1996; 5: 13-24. 29. Ektrand J, Tropp H. The inciden ce of ankle sprains in soccer. Foot Ankle 1990; 11:41-44. 30. Hertel J, Guskiewicz K, Kahl er D, Perrin D. Effect of lateral ankle joint anesthesia on center of balance, postural sw ay, and joint position sense. Journal of Sport Rehabilitation 1996; 5: 111-119. 31. Hertel J. Functional Anatomy, pathomech anics, & pathophysiol ogy of lateral ankle instability. Journal of Athletic Training 2002; 37(4): 364-375. 32. Lynch S. Assessment of the in jured ankle in the athlete. Journal of Athletic Training 2002; 37(4): 406-412. 33. Starkey C. Injuries and illnesses in th e national basketball association: A 10-year perspective. Journal of Athletic Training 2000; 35(2): 161-167. 34. Sterner R, Armstrong C. A force and elec tromyographical analysis of a functional fatigue protocol: a pilot study. Journal of Athletic Training 2001; 36(2): S-31. 35. Reimann B. Is there a link between chronic ankle instability and postural instability. Journal of Athletic Training 2002; 37(4): 386-393. 36. Loudon J, Bell S, Johnston J. The Clinical Orthopedic Assessment Guide 1998. Human Kinetics, Champaign. 37. Marieb E. Human Anatomy & Physiology 1998. Benjamin/Cummings Publishing Co., Menlo Park, CA. 38. Earl J, Hertel J. Lower-extremity mu scle activation during the star excursion balance tests. Journal of Sports Rehabilitation 2001; 10(2): 93-104. 39. Konradsen L, Voigt M, Hojsgaard C. A nkle inversion injuries : the role of the dynamic defense mechanism. The American Journal of Sports Medicine 1997; 25(1): 54-58. 40. Vioght M, Hardin J, Blackburn T, Tippett S, Canner G. The effects of muscle fatigue on and the relationship of arm dominance to shoulder proprioception. Journal of Orthopedic and Sports Physical Therapy 1996; 23(6): 348-352.

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75 41. Anderson S, Terwilliger, Denegar C. Co mparison of open versus closed kinetic chain test positions for measuring joint position sense. Journal of Sport Rehabilitation 1995; 4: 165-171. 42. Lentall G, Baas B, Lopez D, McGuire L, Sarrels M, Snyder P. The contributions of proprioceptive deficits, muscle functi on, and anatomic laxity to functional instability of the ankle. Journal of Orthopedic & Spor ts Physical Therapy 1995; 21(4): 206-215. 43. Prentice W. Therapeutic Modalities in Sports Medicine 1999. McGraw-Hill, Boston. 44. Konradsen L, Ravn J. Ankle instabili ty casued by prolonged peroneal reaction time. Acta Orthop Scand 1990: 61(5); 388-390. 45. Aniss M, Gandevia C, Burke D. Reflex responses in active muscles elicited by stimulation of low-threshold a fferents from the human foot. Journal of Nuerophysiology 1992; 67(5): 1375-1384. 46. Morgoni P, Narici M, Sirtori M, Lore nzelli F. Isokinetic torques and kicking maximal ball velocity in young soccer players. The Journal of Sports Medicine and Physical Fitness 1994; 34(4): 357-361. 47. Negrete R, Brophy J. The relationship be tween isokinetic open and closed chain lower extremity strength and functional performance. Journal of Sport Rehabilitation 2000; 9(1): 46-61. 48. Wilk K, Romaniello W, Soscia S, Arri go C, Andrews J. The relationship between subjective knee scores, isokinetic testi ng, and functional testing in the ACLreconstructed knee. Journal of Orthopedic and Sports Physical Therapy 1996; 20(2): 60-73. 49. Rozzi S, Lephart S, Sterner R, Kuligowsk i L. Balance training for person with functionally unstable vers us stable ankles. Journal of Orthopedic and Sports Physical Therapy 1999; 29(8): 478-486. 50. Konradsen L. Factors contributing to chronic ankle instabil ity: kinesthesia and joint position sense. Journal of Athletic Training 2002; 37(4): 381-385. 51. Reimann B, Caggiano N, Lephart S. Exam ination of a clinical method of assessing postural control during a functional performance task. Journal of Sport Rehabilitation 1999; 8: 171-183. 52. Ross S, Guskiewicz K, Yu B. Time to stabilization differen ces in functionally unstable and stable ankles. Journal of Athletic Training 2002; 37(2): S-22.

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76 53. Goldie P, Evans O, Bach T. Steadiness in one-legged stance: development of a reliable force-platform testing procedure. Arch Physical Medicine and Rehabilitation 1992; 73: 348-354. 54. Dyhre-Poulsen P, Simonsen E, Voight M. Dynamic control of muscle stiffness and h reflex modulation during hopping and jumping in man. Journal of Physiology 1991; 437: 287-304. 55. Devita P, Skelly W. Effect of landing stiffness on joint kinetics and energetics in the lower extremity. Medicine and Science in Sports and Exercise 1992; 24(1): 108-115. 56. Reimann B, Myers J, Lephart S. Sensor imotor system measurement techniques. Journal of Athletic Training 2002; 37(1): 85-98. 57. Bobbert M, van Ingen Schenau G J. M echanical output about the ankle joint in isokinetic plantar flexion and jumping. Medicine and Science in Sports and Exercise 1990; 22(5): 660-668. 58. Caulfield B, Garrett M. F unctional instability of the ankl e: Differences in patterns of ankle and knee movement prior to and post landing in a single leg jump. International Journal of Sports Medicine 2002; 23: 64-68. 59. Demeritt K, Shultz S, Docherty C, Gansneder B, Perrin D. Chronic ankle instability does not affect lower extremity functional performance. Journal of Athletic Training 2002; 37(4): 507-511. 60. Lephart S, Kocher M, Narner C, Fu F. Quadriceps strength and functional capacity after anterior cruciate ligament reconstr uction: patellar tendon autograft versus allograft. The American Journal of Sports Medicine 1993; 21(5): 738-743.

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77 BIOGRAPHICAL SKETCH I was born in Jacksonville, FL, on October 16, 1978, to Mr. Raymond M. Wikstrom and Mrs. Geraldine A. Wikstrom. My younger sister and I grew up as Navy brats, moving around the country. Living in Jacksonville, FL, San Diego, CA, and Alexandria, VA, exposed me to very different and unique views of life. I attended two different high schools: Saint Augustine Hi gh School in San Diego and Bishop Ireton High School in Alexandria. While in school, I lettered in two varsity sports, basketball and tennis, and was a member of the Nati onal Honor Society. I graduated from high school in 1997 and decided to atte nd Roanoke College in Salem, VA. I came to Roanoke to major in athletic tr aining, because of the inspiration givin to me by the program director, Mr. Jim Buria k. While a demanding and time consuming major, I never doubted my decision to become an athletic trainer or my decision to attend Roanoke College. My time there was the best four years of my life. I graduated from Roanoke College in 2001 and was accepted to con tinue my education at the University of Florida. As a first year graduate athle tic trainer, I was sent to be the head athletic trainer at Trenton High School. Despite the sense of overwhelming pressure of being a head athletic trainer for the first time, I felt prep ared and grateful for th e mentoring of Mr. Jim Buriak and Roanoke College. As a second year graduate assistant, I was assigned to be the head athletic trainer at Eastside High School. Eastside has given me the opportunity to grow as a clinician, teacher, and mentor a nd feels like a second home. I will be sad to

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78 leave at the end of this year but excited to be gin a new chapter in my life, as I begin work towards my doctoral degree here at the University of Florida.


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Material Information

Title: Functional Vs Isokinetic Fatigue Protocol: Effects On Time to Stabilization, Peak Vertical Ground Reaction Forces, and Joint Kinematics in Jump Landing
Physical Description: Mixed Material
Copyright Date: 2008

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
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FUNCTIONAL VS ISOKINETIC FATIGUE PROTOCOL: EFFECTS ON TIME TO
STABILIZATION, PEAK VERTICAL GROUND REACTION FORCES, AND JOINT
KINEMATICS IN JUMP LANDING

















BY

ERIK A. WIKSTROM


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE IN EXERCISE AND SPORT SCIENCES

UNIVERSITY OF FLORIDA


2003















ACKNOWLEDGMENTS

Writing this thesis has been one of the most challenging and demanding endeavors

of my academic career, and I could not have done so without the help and support of

several important people. Most importantly, I would like to thank Dr. Mike Powers, my

committee chair, who encouraged my ideas and supported my efforts throughout the

entire process. His ideas and challenges help me to grow both as a student and as a

researcher and make this the best possible study that it could be.

The rest of my committee also deserves a lot of appreciation. Dr. Mark Tillman

was vital in familiarizing me with the lab and equipment that were required to complete

this study. I would also like to thank Dr. Tillman for all his time and expertise helping

me troubleshoot the numerous problems that were encountered along the way. I also

appreciate and thank Dr. Marybeth Horodyski for her continued support and insight into

the entire master's thesis process.

I would also like to take this opportunity to thank doctoral student Gary Porter for

his time that was spent revising my chapters and advising me during the whole writing

process. Lastly I would like to thank my friends and family whose constant support and

encouragement were invaluable to me in completing this thesis and keeping me sane

when the bear was winning.
















TABLE OF CONTENTS
page

A C K N O W L E D G M E N T S .................................................................................................. ii

LIST OF TABLES ..................................................... vi

LIST OF FIGURES ........................................... ............................ viii

ABSTRACT ............................................................................. x

CHAPTER

1 IN TR O D U C T IO N ........ .. ......................................... ..........................................1.

Statem ent of the P problem ...................................................................... ...............2...
Hypotheses ............................................. ................................. 2
D definition of Term s ......................................................................................... . 3
Assumptions .............. ............................................ ....... 4
Limitations ............................................ ................................. 4
Significance .............. .....................................................................4...........

2 R E V IEW O F L ITER A TU R E ........................................... ....................... ............... 6

Introduction .................................................................................... . .. ...............6
T alo cru ral Joint...................................................... ............................................ . 7
T im e to Stab ilization ... ... ........................................... ....................... .. .......... ... 10
M easurem ent of Postural Sw ay ..................................... ..................... ................ 14
G round R action Forces .................................................................... ............... 15
F atig u e P ro to c o ls ........................................................................................................ 17
C conclusion .............. ........................................................................ . ..... 2 1

3 M E TH O D S .............. ....................................................................... . ......23

Subjects .............................................. .................................. 23
Instrum entation ..................................................................................................... 23
M medical Eligibility Form ..................................................................................23
V ertical Jum p Station ..................................................................... ...............23
Isokinetic D ynam om eter ..................................................................................24
T riaxial F orce P late ..........................................................................................24
Infrared Tim ing D evice ....................................................................................24
M otion A analysis System ...................................................................................24









M e a su re m e n ts .............................................................................................................2 5
Tim e to Stabilization ............. ................. .............................................. 27
G round R action Forces ................. .......................................................... 28
M option A analysis .............. ................. ..... ............................. 28
Isokinetic F atigue P rotocol ......................................... ........................ ................ 30
Functional Fatigue Protocol ..................................... ........................ ............... ...... 33
The SE M O A gility D rill .................................... ....................... ................ 33
P lyom etric B ox Jum ps......................................... ........................ ................ 33
Tw o-legged H op Sequence............................................................. ................ 34
Side-to-side B ounds ........................................................................ .............. 34
M ini-tram p ...........................................................................................................34
C o-contraction A rc .............. .... ............. ................................................ 34
P ro c e d u re .................................................................................................................... 3 5
D ata A analysis ..............................................................................................................38

4 R E S U L T S .......................................................................................... ..................... 4 0

Introduction .................................................................................. ....................... 40
Subj ects ............................................... ................................. 40
T im e to Stabilization ................................................................................................4 1
V vertical .............. ....................................................................... . .... 4 1
M e d ia l/L ate ra l .....................................................................................................4 1
A nterior/P osterior .............................................................................................42
G round R action Forces ..........................................................................................42
Jo in ts K in em atic s ........................................................................................................4 3
D orsiflexion ................................................................................................... 43
K nee Flexion ................................................................................................. 44
K nee V algum .................................................................................................. 44
Correlational Analysis ......................................................................45

5 D ISC U SSIO N ............................................................................... ....................... 47

F a tig u e ........................................................................................................................4 7
Jum p Landing Protocol .........................................................................................50
V validity of M measure ............................................................................................... 52
G round R action Forces ..........................................................................................53
Joint K inem atics .......................................................................................... . 54
C correlation .............. ........................................................................ . ..... 54
Indications ................................................................................... ...................... 54
C conclusions ..........................................................................................................55
S u m m a ry .................. ..... ........................................................................................5 5
Im plications for Future Research.............................................................................56

APPENDIX

A LETTER OF INFORMED CONSENT .................... ...................................58



iv










B MEDICAL ELIGIBILITY QUESTIONAIRE....................................................... 61

C DATA COLLECTION FORMS..............................................................................62

D A N O V A T A B L E S .................................................... ............................................. 64

E R A W D A T A TA B L E S ... .......................................................................................67

Isokinetic P rotocol D ata .. ..................................................................... ................ 68
F unctional P rotocol D ata ............................................. ......................... ................ 70

L IST O F R E F E R E N C E S ................................................... ........................................... 72

BIOGRAPHICAL SKETCH .................................................................................... 77









































v















LIST OF TABLES

Table page

4-1 Vertical TTS as determined by vertical GRF-Fz (mean SD)...............................41

4-2 Medial/Lateral TTS as determined by GRF-Mx (mean SD) ...............................41

4-3 Anterior/Posterior TTS as determined by GRF-My (mean SD)........................42

4-4 Toe Strike-Fl as determined by GRF-Fz (mean SD).......................................43

4-5 Heel Strike-F2 as determined by GRF-Fz (mean SD) ......................................43

4-6 A nkle Flexion (m ean SD ) ....................................... ....................... ................ 44

4-7 K nee F lexion (m ean SD )......................................... ....................... ................ 44

4-8 K nee V algum (m ean SD ) .................................... ....................... ................ 45

4-9 Pearson Product Moment Correlation (r and significance).................................46

D -1 V ertical TT S A N O V A table....................................... ...................... ................ 64

D -2 M edial/Lateral TTS AN O V A table..................................................... ................ 64

D-3 Anterior/Posterior TTS ANOVA table ...............................................................64

D -4 G R F-F 1 A N O V A table ................................................................... ................ 65

D -5 G R F-F2 A N O V A table ................................................................... ................ 65

D -6 A nkle Flexion A N O V A table.............................................................. ................ 65

D -7 K nee Flexion A N O V A table ...................................... ...................... ................ 65

D -8 K nee V algum AN O V A table ..................................... ...................... ................ 66

E -1 Subject D em graphics ...................................................................... ................ 67

E -2 P retest Isokinetic D ata ............................................................................ ................ 68

E -3 P osttest Isokinetic D ata ......................................................................... ................ 69









E-4 Pretest Functional D ata. ............................................ ......................................... 70

E-5 Posttest Functional D ata ....................................................................... ................71















LIST OF FIGURES

Figure page

2-1 A interior view of ankle m ortaise ........................ .............................................. 10

2-2 Medial or Deltoid ligament of the ankle ............................................................. 10

2-3 L ateral ligam ents of the ankle ..................................... ..................... ................ 10

2-4 Force time history of a flat foot landing.............................................................. 17

2-5 Force time history of a toe to heel landing ................ ................................... 17

3 -1 V ertec ju m p station n ..................................................................................................2 5

3-2 Isokinetic dynam om eter........................................................................ ................ 25

3-3 B ertec triaxial forceplate ....................................................................... ................ 25

3-4 B row er infrared tim ing device .................................... ..................... ................ 26

3-5 JVC low speed motion recorder camera .............................................................26

3 -6 Ju m p p roto co l ........................................................................................................... 3 0

3-7 Graphical representation of sequential estimation .............................................30

3-8 Vertical time to stabilization analysis method. ............................. ..................... 31

3-9 Force time history curve with GRF collection points highlighted........................31

3-10 C am era setup for m otion analysis ............................................................................32

3-11 Placem ent of reflective m arkers .......................................................... ................ 32

3-12 Subject position for isokinetic fatigue protocol ..................................................35

3-13 SEMO agility drill ...................... .... .......... ......... ............... 35

3-14 Plyom etric box jum ps. ...................................................................... ................ 36

3-15 Tw o-legged hop sequence ........................................ ........................ ................ 36









3-16 Side-to-side bounds ........................ .. ....................... ..................................... 36

3-17 Mini-tramp jumps ...................... ........... .....................................37

3-18 C o-contraction arc drill. ................. ............................................................... 37

5-1 Peak vertical GRF at heel strike (F2) ................................................. ................ 53















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science in Exercise and Sport Sciences

FUNCTIONAL VS ISOKINETIC FATIGUE PROTOCOL: EFFECTS ON TIME TO
STABILIZATION, PEAK VERTICAL GROUND REACTION FORCES, AND JOINT
KINEMATICS IN JUMP LANDING

By

Erik A Wikstrom

May 2003

Chair: Michael E. Powers
Major Department: Exercise and Sport Sciences

Dynamic stability provides inherent protection against joint injury and several

studies have examined the influence of fatigue on neuromuscular control and joint

stability. Thus, the purpose of this study was to compare the effects of an isokinetic(IFP)

and functional fatigue protocol (FFP) on stabilization time (TTS), ground reaction forces

(GRF) and joint angles following a jump landing. Twenty healthy subjects (age=221.6

yrs, height=173.8410.452 cm, mass=67.1312.426 kg) were assessed for the designated

events. Subjects completed three jump landing tasks, requiring a two-legged jump at

50% of their maximum jump height to the center of a force plate 70-cm from the starting

position. Immediately following, each subject completed either the FFP or the IFP.

Fatigue was considered to have occurred when time to completion of the FFP increased

to 150% of the initial time to completion or failure to produce 50% of the initial IFP peak

torque. Immediately following fatigue, post testing was performed. TTS was determined









as the point where the sequential average of the vertical ground reaction force data points

fell within .25 standard deviations from the mean of the initial 3-sec collection period.

Two way repeated measures ANOVA revealed no significant differences when

comparing isokinetic to functional fatigue values for vertical TTS [F(1,19)= 3.93,

p=.538], medial/lateral TTS[F(1,19)= .287, p=.598], anterior/posterior TTS [F(1,19)=

.001, p=.978], toe touch GRF [F(1,19)=.121, p=.286], and heel strike GRF (F=3.673,

p=.070). Also, no significant differences were revealed when comparing the fatigue

protocols for ankle Dorsiflexion [F(1,19)= .06, p=.803], knee flexion [F(1,19)= .21,

p=.652], and knee valgum [F(1,19)= .79, p=.386].

The results of this investigation suggest that the specific fatigue protocol used did

not impair dynamic stability and that future research should focus on fatigue that occurs

during athletic competition and the correctness of the measure of time to stabilization.














CHAPTER 1
INTRODUCTION

Athletes at all levels of competition may eventually suffer from an ankle injury.

While the exact cause of these injuries is unknown, a vital component of preventing an

injury is the athlete's neuromuscular control. Neuromuscular control is dependent on the

central nervous system (CNS) to interpret and integrate proprioceptive and kinesthetic

information. This information identifies the joint's ability to sense its position in space

and to sense motion of the corresponding body segments.1-3 After receiving this

information, the CNS must then control individual muscles and respective joints involved

in specific motions to produce safe coordinated movement.2'4 While all aspects of

neuromuscular control are important to athletes in preventing and rehabilitating injuries,

postural control has been have been demonstrated to be important.

Athletes who have better postural sway are less likely to suffer ankle injuries in

subsequent athletic seasons.. Postural control is a complex coordination of sensory and

biomechanical information and muscular exertion on external forces.2'8-11 A loss of any

of these factors can lead to increased postural sway and a decreased ability to control a

body part or the body as a whole during athletic activity.

Time to stabilization is the body's ability to minimize postural sway when

transitioning from a dynamic to static state, thus a very functional test. 12,13 As a form of

postural control, TTS involves a complex coordinated effort between the sensory and

mechanical systems of the body as well as a series of powerful contractions of lower leg

musculature and synergistic stabilizers throughout the lower extremity.10









It has been suggested that even healthy athletes may suffer lower extremity injuries

during an athletic event due to the fatigue of those muscles resulting in a decrease in

neuromuscular control.9'14-16 These studies focused on lower extremity fatigue induced

isokinetically. Thus, fatigue could be quantified as a percent of peak torque. Yet, very

little research has focused on neuromuscular control following a functional fatiguing

protocol.

Statement of the Problem

Many authors have studied the effects of muscular fatigue on postural control by

isokinetically fatiguing their subject's lower extremity musculature.9'16-18 These studies

have generally shown an increase in postural sway after muscular fatigue. However, very

little research has examined functional fatigue protocols19'20 of the ankle and their effects

on time to stabilization, a more functional test of postural control. Thus, the purpose of

this study is to compare and correlate an isokinetic fatigue protocol's effects on TTS,

peak vertical ground reaction forces and biomechanical effects (i.e., ankle and knee

flexion and knee valgum) during a single-leg-hop stabilization test to those of a

functional fatigue protocol, which is similar to actual athletic practice and game

situations.

Hypotheses

There have been three hypotheses made for this investigation.

* All subjects performing fatigue protocols (i.e., isokinetic, functional) will have
significant increases in time to stabilization, peak vertical ground reaction forces,
and stated biomechanical effects as compared to the pretest measure.

* There will be a significant increase in subjects' time to stabilization, peak ground
reaction forces, and stated biomechanical effects following the functional fatigue
protocol as compared to the isokinetic fatigue protocol.









* There will be a high correlation between peak vertical ground reaction forces and
time to stabilization in both the pretest and posttest of both fatigue protocols.

Definition of Terms

The following terminology will be referred to throughout this research study.

These definitions are provided to clarify the exact parameters that were being studied.

* Functional fatigue protocol: Related to the muscular exertion of the lower
extremity when performing a sports-specific series of agility drills in an effort to
establish a reliable application to athletes in competition. The protocol in this
experiment incorporates the: SEMO agility drill, plyometric box jumps, two-legged
hop sequence, side-to-side bounds, mini-trampoline balance series, and the co-
contraction arc drill.

* Isokinetic fatigue protocol: Chosen for its inherent objectivity, patient safety, and
reproducibility. It is related to the muscular exertion of the lower extremity when
performing a series of isokinetic maximal contractions. The protocol for this
experiment incorporates continuous maximal concentric contractions of dorsi
flexion and plantar flexion at the ankle.12

* Postural control: A measure of balance or postural stability. It is the amount a
body's center of mass moves within or around its base of support.11,21

* Proprioception: The awareness of postural movement, the changes in equilibrium,
and the knowledge of position, weight, and resistance of objects in relation to the
body.1'8

* Stability: The ability to transfer vertical projection of the center of gravity to the
supporting base while keeping the knee as still as possible.12

* Stabilometry: The common means of objectively detecting proprioceptive deficits
and quantitatively measuring aspects of proprioception.22

* Time to stabilization: A valid and reliable technique to measure balance. The
method involves landing on a force plate from a dynamic state, and transitioning
balance into a static state.12'13'23

* Peak vertical ground reaction force: The maximum force or heaviness of a
landing. Measured in newtons, it accurately depicts how hard or soft an individual
landed from a jump. Ground reaction forces are often expressed as the magnitude
of the peak vertical force divided by the subject's body weight, or units of body
weight.24

* Biomechanical Effects: The changes that occur in joint angles (i.e., ankle flexion,
knee flexion, and knee valgum) from a non-fatigued to a fatigued jump landing.









Assumptions

There are six assumptions made for this research study.

* All subjects were truthful in reporting previous history of lower extremity and head
injury and disorders that affect equilibrium.

* All subjects will give a maximal effort during their testing and treatments.

* Results of this study are representative of all individuals with no prior history of
lower extremity and head injury and disorders affecting equilibrium.

* That the functional fatigue protocol was an effective method of fatiguing the
musculature of the lower leg.

* That the isokinetic and functional fatigue protocols were equivalent in their ability
to each fatigue their subjects to the level required, so as not to skew the results.

* That the testing protocol mimics actual athletic activity and is an accurate measure
of time to stabilization.

Limitations

There are five limitations identified for this research study.

* Subjects wore different brands of shoes, although all a similar style during the
fatigue protocols.

* Subjects were not familiar with the fatigue protocols.

* Subjects were not familiar with the testing procedures.

* Only one type of isokinetic fatigue protocol was used.

* Only one type of functional fatigue protocol was used.

Significance

This study will test an isokinetic fatigue protocol of the lower leg musculature and

its effects on time to stabilization and peak vertical ground reaction forces as compared to

a functional fatigue protocol of the lower leg musculature. Through the examination of

the main effects of the fatigue protocols and the tests performed, a highly positive

correlation will be illustrated. More importantly, a significant difference in the main






5


effects and the interaction of the fatigue and tests (i.e., time to stabilization, peak vertical

ground reaction forces, biomechanical effects) will strongly suggest that isokinetic

fatigue protocols do not mimic functional activity. These results will provide practical,

clinical applications, regarding how functional fatigue increase time to stabilization,

allowing clinicians to focus on improving postural control in their athletes. However,

these results will also benefit researchers indicating that a functional fatigue protocol is a

more reliable method of mimicking the fatigue that takes place during athletic activity.














CHAPTER 2
REVIEW OF LITERATURE

Introduction

Injuries to the ankle or talocrural joint can occur in any sport because the ankle is

the focal point to which total body weight is transmitted to during ambulation.25

Therefore the talocrural joint is one of the most common areas for injury in the athletic

population, specifically the stabilizing ligaments of the joint.7'22'26-33 Starkey33 reviewed

injury data over a span often years for the NBA, and found that the most common site of

injury was the ankle joint. Ankle injuries accounted for more than 10% of all injury

occurrences, and 11% of time lost due to injuries. Similar observations have been

reported elsewhere.28'29 According to Ekstrand and Tropp29 approximately 40% of all

injuries occur at the ankle joint. Anecdotally, most of these injuries occur at the end of

activity when the athlete is fatigued.16

Ankle sprains, which affect the stabilizing ligaments, are caused by sudden

inversion or version forces that overwhelm the ankle's defenses (i.e., proprioception,

muscular strength).25 These forces are often combined with plantar flexion and result in

the stretching or tearing of the peroneal muscles and or stabilizing ligaments3 While

relatively minor injuries, ankle sprains can result in a great deal of missed athletic

participation. Therefore, measures to prevent the mechanisms of injury need to be

studied to reduce or prevent ankle injuries as much as possible.

Several theories have been explored as to the cause of ankle injury. These causes

can be broken into extrinsic and intrinsic factors3'4'30 Extrinsic factors include poor









equipment, improper shoes and playing surface. Intrinsic factors include muscular

fatigue, excessive pronation and ligament laxity. All these factors taken individually or

in combination can lead to ankle injuries. Muscular fatigue of the lower extremity has

been one of the focus of recent studies, in an attempt to better understand its direct effect

on ankle and how it predisposes the ankle to injury.9'14-19'34

Fatigue of the lower leg musculature is controversial as to its importance to

increasing postural sway. Motor control of an extremity is dependent on proprioceptive

feedback and reflexive and voluntary muscle responses.9'35 Muscular fatigue could

negatively affect proprioception through either deficiencies in the activation of the

muscular mechanoreceptors or a decrease in the muscular function. These deficiencies

have been credited through a positive correlation between muscular fatigue, quantified as

50% of the initial baseline test, and a decrease in postural control during several

studies.9'16-19 Most of these correlations have used isokinetic fatigue protocols in a non-

weight bearing position, and with postural control testing methods and protocols

conducted in full-weight bearing positions.

Talocrural Joint

The ankle joint (talocrural joint) is made up of three bones; the tibia, fibula and the

talus. The tibia, the weight bearing bone of the lower leg, is affixed to the fibula via

several ligaments. The distal aspects of these bones (i.e., medial and lateral malleolus)

form the ankle mortise (Figure 2-1), in which the head of the talus sits and rocks in an

anterior/posterior direction during ambulation.3'25'30'36'37

The articulation of this joint forms a strong preventative measure against medial or

version ankle sprains because the medial malleolus extends significantly more distally

than the lateral malleolus which forms a bony block that limits talar abduction. The









anatomical failure of the body to prevent lateral ankle sprains with bony defenses causes

the ligaments and musculature of the lower leg to play a vital role in stabilizing the ankle

from lateral sprains. The stabilizing ligaments of the ankle joint, which protect the ankle

in three distinct areas and from different motions, are the tibiofibular, lateral, and medial.

The tibiofibular ligament is the distal and proximal extremes of the interosseous

membrane that transverses the entire lower leg, connecting the tibia and fibula.36'37 The

oblique arrangement of the tibiofibular ligaments aid in the distribution of force placed

upon the lower leg and stabilizes the ankle from rotation forces during activity.3'25'30'37

The medial or deltoid ligament (Figure 2-2) is the primary resistance against version of

the ankle and is the strongest ligament in the talocrural joint.3'25 The deltoid ligament is

actually four ligaments that act as an interconnected fan, increasing its strength and

decreasing its incidence of injury. The ligaments of the medial aspect of the ankle

originate collectively at the medial malleolus of the tibia and insert individually to the

talus, calcaneous, and navicular.3'4'30'36'37

The lateral ligaments of the talocrural joint (Figure 2-3) also collectively originate

at a common site, the lateral malleolus of the fibula, and insert at the talus and

calcaneous. These ligaments, named after their respective insertions are the anterior-

talofibular (ATF), the calcaneofibular (CF), and the posterior-talofibular (PTF).

Individually, none of these lateral-stabilizing ligaments are as strong as the deltoid

ligament structure.25 The ATF has the highest incidence of injury in the ankle joint

because it is the first ligament to undergo stress when the ankle is inverted and

plantarflexed.11'25 The CF ligament situated vertically is usually only injured during

severe grade two ankle sprains, while the PTF ligament is the strongest of the lateral









ligaments and is usually uninjured, except in the most severe ankle sprains.25

Collectively these stabilizing ligaments protect the ankle from inversion forces, while the

ATF and PTF also prevent anterior and posterior translation of the talus in their

respective directions.3'11

Supporting the stabilizing ligaments are the surrounding muscles of the lower leg.

These muscles, respective nerves and vascular supply are divided into four main

compartments that serve different functions.3'25'37 The anterior compartment contains the

anterior tibialis and toe extensors, which are the primary and secondary dorsiflexors of

the foot respectively. The lateral compartment holds the peroneals, which are the main

evertors of the foot and prevent excessive inversion during activity. The posterior tibialis

and toe flexors make up the deep posterior compartment, which are secondary investors

and plantar flexors of the foot. The final compartment is the superficial posterior that is

made up of the gastrocnemius and soleus muscles, the main plantar flexors of the foot

and main stabilizers of ankle motion.3',4,25 While all the muscles mentioned are

important, weakness of the peroneals and gastrocnemius/soleus complex would more

significantly put an athlete at risk to injury, specifically to inversion ankle sprains.38'39

The ankle joint, while stable during daily activities undergoes extreme forces

during athletic competition, which places increasing stress at the lateral aspect of the

joint. This additional stress is focused on an area that is anatomically weak, increasing

the ankle joint's incidence of injury. The intrinsic factor of muscular fatigue on postural

control, becomes increasingly important in the body's effort to maintain its center of

balance and preventing lateral ankle sprains, in a weak anatomical area.


























Figure 2-1. Anterior view of ankle mortaise; tibia(l), fibula(2), talus(3).

Deltoid Ligament
Pntorwt Tbwtoiwfaf Tnti


-F-- Swt.m.ciiuarS


Figure 2-2. Medial or Deltoid ligament of the ankle

Lateral View f Ankle


Tibia





Tal- -A


Calcaneo-
fibular


Fibula


Tkflbfialar


Figure 2-3. Lateral ligaments of the ankle.









Time to Stabilization

Time to stabilization, a form of postural sway, is defined as the time that is required

to reach stability after landing. 10,22 Increased postural sway is a negative factor that can

lead to increased incidence of injury caused by diminished factors of neuromuscular

control and or balance.5'7 Proprioception is defined by Reimann and Lephart2 as the

ability of a joint to determine its position in space; detect movement, kinesthesia, and

sense resistance acting on it. The importance of understanding proprioception and

kinesthesia during athletic competition is vital to preventing injuries. Without sufficient

proprioceptive and kinesthetic awareness, the body would not be able to respond to

changes in joint angles, inhibiting the joint's ability to protect itself from extreme motion

or forces that would cause damage to soft tissue or bone.

Hoffman and Payne22 and Johnston et al.9 attribute the diminished ability to detect

motion and joint position sense to a decreased accuracy of afferent input and efferent

output or an increase in muscular fatigue. The afferents that are responsible for the

response time of muscular activation, to maintain the body's center of balance, are

mechanoreceptors1'9'11'40 These mechanoreceptors are located in the joints and muscles of

the body,1'3'9'11'39'41 and include the joint mechanoreceptors: Ruffini's endings, Pacinian

corpuscles and free nerve endings.1'11'37 The mechanoreceptors interpret the joint's

position and detect a passive or active movement of the joint in both closed and open

kinetic chains. Muscle mechanoreceptors, such as muscle spindles and Golgi tendon

organs located in the muscles and tendons, are responsible for sensing changes in muscle

length and tension respectively.1'8'11'40 Together these receptors relay information to the

central nervous system (CNS) regarding changes occurring in and around the joint to help

keep the body within its center of balance.1,4,11,37,40,42,43 A decrease in the efficiency of









these mechanoreceptors would increase the latency period of the reacting joint

musculature.2,11,30,35,44

An increase in reaction time due to malfunctioning mechanoreceptors allows a joint

to be dangerously extended beyond normal anatomical ranges of motion. This contortion

is accomplished because the surrounding muscles (i.e., gastrocnemius, peroneals) may

not fire as quickly and then could not correct the body's center of balance. This

inhibiting factor of mechanoreceptor deficiencies can be complicated further by muscular

fatigue.

McKinely and Pedotti10 noted that the subjects with the shortest time to

stabilization had all three major muscles of the lower leg gastrocnemiuss, soleus, anterior

tibialis) contracted prior to landing. This contraction creates greater muscle stiffness,

which would allow faster reaction to the landing surface. Subjects with poor time to

stabilization scores showed little to no anticipatory control contraction of lower leg

musculature as measured by electromyography.10

Aniss et al.45 provided another insight into a decreased time to stabilization score.

The study examined the various gains of cutaneomuscular reflexes evident in extensor

and flexor muscles of the lower leg. These data indicated that these reflexes are only

present when their respective muscles are in contraction. Aniss et al.45 and McKinely and

Pedotti10 indicated that an association exists between anticipatory or voluntary

contraction of the lower leg musculature and a decrease in reaction time for the

cutaneomuscular reflexes of the lower leg and time to stabilization, respectively. This

would decrease time to stabilization and if fatigue decreases force output in musculature,









then pre-landing contraction at the end of an activity might also be decreased and not

strong enough to excite the cutaneomuscular reflexes.45

Konradsen et al.39 determined through a clinical experiment that the latency period,

response to stimulus, of the peroneals was too long to prevent ligamentous overload in

the clinical setting. Kondradsen et al.39 also concluded that during activity, the ankle

joint and respective musculature receives information from the receptors near the ankle

and foot, rather than from visual or vestibular information, since those sensory inputs

were not denied to the subjects during the experiment. This study supports the data

collected by McKinely and Pedotti10 and Aniss et al.45 that anticipatory contraction of the

lower leg musculature is a prime stabilizing factor of the ankle.

Recent studies have reported positive correlations between muscular fatigue and an

increase in postural sway and time to stabilization.9'16-19 As stated earlier, time to

stabilization, an aspect of motor control for the lower extremity, is dependent on

proprioceptive and kinesthetic feedback as well as reflexive and voluntary muscle

responses.9 Muscular fatigue would negatively affect this proprioceptive feedback loop

through either deficiencies in the activation of the muscular mechanoreceptors or a

decrease in the force produced by muscular function. Decreases in activation of

mechanoreceptors increase the latency period of the muscle action and prolongs the time

to correction and regaining the individual's center of balance.10,39,45 Muscular fatigue

also decreases the force production of a muscle when measured via isokinetic fatigue

protocols.9'14'16-18'46-48 These protocols often indicate a subject is fatigued when peak

torque falls below 50% of the initial contraction.9'16'17'19'20 Thus a delayed firing of the









corresponding musculature with a decreased force production may exponentially increase

injury risk and incidence.7'44'45'49

Because of these data from isokinetic fatigue protocols, there have been several

training protocols established to help injured athletes regain proprioception, potentially

reducing time to stabilization indirectly. While the protocols vary in specific

components, most encompass a single leg balance program, focusing on maintaining the

center of gravity within the base of support.11,49 Common ways of training include

maintaining center of balance on a stable surface and progressing to an unstable surface

(i.e., a wobble board). These training programs require a significant amount of balance

and motor control, while acclimating the muscle to fatigued conditions. Konradson50

illustrated that proprioceptive training can be 80% effective in reducing the frequency of

ankle sprains.

Measurement of Postural Sway

Training protocols can only be effective and measured if there is a baseline to

measure postural sway against. Several valid and reliable testing methods are available

including the single leg balance, Balance Error Scoring System and Star Excursion test.

However, more functional and dynamic measures of time to stabilization can be

measured using single-leg-hop stabilization test on force plates. However, according to

Reimann35 there is no relationship between static and dynamic measurements of postural

sway.

One possible technique to measure balance is stabilometry22 often seen in the form

of a Biodex stability system (BSS).21'51 Stabilometry is a technique that utilizes a force

plate to measure the displacement of an individual's center of gravity while standing in a









static state. While indicating a reliable measure of balance, these data points were also

comparable to studies performed using static force plates.21

Force plates are more often used to determine stability2-center of pressure or

ground reaction forces for a single limb stance.12'13'51 These measurements are obtained

though measuring force at three or more points on the platform or the torque around the

horizontal axes.7'13 Time to stabilization is a functional exam of stability by definition,

forcing subjects to maintain balance through a transition from a dynamic to a static

state.13 Two common methods for this transition are the step down or hop tests.

Respectively, the subject would step down off an elevated platform or hop a set distance

with a minimum height requirement, land on the force plate and regain their center of

balance.12'52 Goldie et al.53 developed a testing protocol that was reliable and minimized

lost data due to subject mortality. This protocol also noted that ground reaction forces

produced more reliable results than center of pressure scores.13,51,53

Ground Reaction Forces

Ground reaction forces (GRF) are a method of measuring balance by measuring the

torque around two horizontal and one vertical axes.13 These forces are indicators of how

heavily an athlete lands from a jump, and how well they balance in a stance, making a

good measure of the time it takes that athlete to stabilize their body mass within their

center of gravity. GRF acting on the body during landings have been associated with

injury to the lower limb.24'26

Ground reaction forces and center of pressure measures have been used repeatedly

in single stance tests of balance and stabilometry. Goldie et al.13 found that GRF were

more reliable indicators of balance and stabilization of the subject than center of pressure

measures. Previous studies have also shown the reliability of this measure to be high.









Ground reaction forces are often expressed as the magnitude of the peak vertical force

divided by the subject's body weight, or units of body weight.24

There are two common appearances of ground reaction forces, that of athletes who

land flat footed (Figure 2-4), and that of athletes who land with a toe-heel technique

(Figure 2-5).26 The flatfoot method produces a unimodal, while the toe-heel method

produces a bimodal ground reaction force-time history.26 The more practiced landing

technique, the toe-heel, produces to maximum force outputs on the bimodal curve from

forefoot and heel contact respectively.26'54 Recent studies have shown peak vertical

GRFs as high a 6.0BW.26

However, little research has been done to illustrate the effects of fatigue on GRF,

most of the research has focused on style of jump, and landing technique. The effects of

fatigue on GRF could be very significant, as joint angles and muscle stiffness at touch

down play a major role as to the magnitude of the peak vertical GRF.

Landing from any jump requires the body to produce movements which will further

minimize the GRFs and soften the landing.10,55 According to Dufek and Bates26, the

height of a jump plays a minor role in the magnitude of GRF as compared to knee joint

angle at touch down. This theory is backed by studies that show a toe-heel landing as

opposed to a flatfoot landing, requires greater joint flexion to decrease GRFs.24'26

In an attempt to reduce GRF the body must anticipate the landing and prepare for it

by increasing muscle stiffness.10,55 Activation of the lower extremity musculature,

specifically the triceps surae complex will help slow the rate of decent and decrease

ground reaction forces on the body. Further reduction of GRFs can be accomplished by

allowing the knee and hip to flex more which increases the time of landing providing an









attenuation in kinetic energy.10,24'55 A deficiency in the body's ability to produce

anticipatory contractions and eccentrically contract lower extremity musculature in a

controlled manner would drastically increase GRF as well as an athlete's time to

stabilization.24 These deficiencies are often caused by fatigue of the lower extremity

through participation in athletic events.


Figure 2-4. Force time history of a flat foot landing.


Figure 2-5. Force time history of a toe to heel landing.











Fatigue Protocols

Fatigue protocols are often used to mimic a subject's loss of power output during

an athletic event. Fatigue is defined as an inability to produce an expected force or power

output, which negatively affects proprioception through either deficiencies in activation

of the muscular mechanoreceptors or a decrease in the muscular function.15

Traditionally, isokinetic fatigue protocols are used to mimic the fatigue that occurs during

an athletic event. These protocols often quantify fatigue at 50% of the initial peak torque

generated by the subjects.9'16-18 The testing protocols of previous research have been

conducted at both high and low angular velocities and varying repetitions. The isokinetic

fatigue protocol ends traditionally when three consecutive repetitions are below 50% of

the initial peak torque, to ensure that fatigue and not lack of effort is indicated by the

torque values.9'16-18

The purpose of these isokinetic fatigue protocols is to isolate particular muscles and

to determine each muscle's role in establishing and controlling time to stabilization.

Isokinetic testing provides a fixed speed with a varying resistance to allow for maximal

effort throughout a range of motion (ROM).3'4'56 Using isokinetic machines, the ROM of

a joint and the strength of a group of muscles can be assessed. Isokinetic testing provides

information such as peak torque, average power and total work done, as well as the

subject's fatigue index. Isokinetics allow athletes to perform exercises at a more

functional speed than isotonic exercise; a fixed resistance, varying speed exercise.3'4 The

majority of isokinetic testing is done via open kinetic chain (OKC) positioning. An open

kinetic chain indicates that the distal extremity, in this case the foot, is not fixed and can

move freely without affecting the performed exercise. The counter position is a closed









kinetic chain (CKC) which has the distal extremity, hand or foot, attached to the ground

or stable platform.3'20'28'41'47 Open kinetic chain testing is non-weight bearing and

therefore, does not account for the stabilizing effects that secondary and synergistic

muscles play during closed kinetic chain (CKC) weight-bearing exercises.

Bobbert and van Ingen Schenau57 compared the mechanical output of the ankle

during isokinetic plantar flexion and single-leg jumping. The results indicated that at a

given angular velocity of plantar flexion much larger moments were produced during

jumping than isokinetic plantar flexion.57 Bobbert and van Ingen Schenau57 reasoned

that during isokinetic testing the duration of plantar flexion is so short, that the

gastrocnemius can not rise to the maximum strength potential and produces a

submaximal muscle moment. Also the positioning of isokinetic testing places the

muscle fibers of the plantar flexors in an unfavorable area of their force-velocity

relationship.57

Despite the limitations of isokinetic testing, several studies have indicated a

positive correlation between isokinetic peak torque and functional ability. Wilk et al.48

investigated the relationship between isokinetic knee extension strength and functional

testing. The results indicated a positive correlation between isokinetic strength and

functional ability. The results from Negrete and Brophy47 demonstrated the same

relationship. While the data indicated a positive correlation, only the Negrete and

Brophy47 results were significant. Similarly, Morgoni et al.46 compared isokinetic peak

torque to maximal ball velocity in young soccer players. These data illustrated a

significant and positive correlation between isokinetic peak torque and functional ability.









OKC isokinetic fatigue protocols have also indicated a positive correlation between

fatigue and an increase in postural sway. Johnston et al.# indicated significant differences

in postural sway after conducting isokinetic fatigue protocols. In another study,

Vuillerme et al.15 also indicated significant increases in postural sway after muscle

fatigue was induced via an isokinetic protocol.

Regardless of these correlations, a more clinically relevant protocol would be CKC,

weight-bearing testing. Recently there have been studies done to investigate close kinetic

chain isokinetic testing.9'2 ,41,47 These studies have suggested positive correlations

between the open and closed kinetic chain isokinetic testing protocols.20'47 However, it

should be noted that most of these protocols compare peak torque to a maximal strength

test. Porter et al.20 conducted a study that illustrated a way to measure standing isokinetic

peak torques for dorsiflexion and plantarflexion. In this study, a positive strength

correlation was indicated between the non-weight and weight-bearing isokinetic test

positions. This could indicate that isokinetic testing is a valid and reliable method of

measurement, but no correlations have been noted at this time regarding isokinetic

fatigue protocols and functional fatigue protocols.

While several other studies have indicated that a positive correlation between

isokinetic strength and functional ability does exist, very little research has been done to

determine the validity of isokinetic fatigue protocols. To the best knowledge of the

researchers, no study has investigated and compared the effects of an isokinetic fatigue

protocol and a functional fatigue protocol on time to stabilization. Functional fatigue

protocols may consist of any number of CKC weight-bearing activities that include

dynamic movement and require stabilizing effects of the musculature. Sprints19, toe









raises1 and cutting34 are just a few examples of functional activities that can be used in a

fatigue protocol. Though little research has focused on functional fatigue protocols,

several studies have found that postural control has increased significantly with

functional fatigue. 12,19

Conclusion

The ankle joint, supported by stabilizing ligaments and surrounding musculature, is

the focal point for the body's weight during ambulation. Due to the significant amount of

weight placed upon the joint and the inherent instability of the ankle, the ankle is the

most commonly injured body part during athletic competition.22,24,26,28,33 Ankle sprains,

especially lateral, often become chronic injuries due to the incomplete rehabilitation

process that does not address the decreased neuromuscular control and the increased time

to stabilization resulting from the injury.

Time to stabilization, or the amount of time for the body to regain the center of

balance or mass within it's base of support, and can be affected by several factors

including injury or a prolonged response time to afferent neural signals caused by

muscular fatigue. This increased response time, quantified in time to stabilization,

inhibits the already destabilized ankle joint during dynamic movement and increases the

chance for injury. To determine the increased response time, subjects must stabilize

themselves on a force plate.

The majority of the research investigating the effects of muscular fatigue on

postural sway and time to stabilization utilized an isokinetic protocol. Isokinetic

protocols are frequently chosen because of the inherent safety to patients, their

objectivity, and their reproducibility in testing measures.15 However, the validity of

isokinetic fatigue protocols has not been addressed. To determine if OKC isokinetic






22


fatigue protocols are a true measure of the fatigue experienced during athletic activity,

they must be compared to functional fatigue protocols. Any number of CKC weight-

bearing activities can be incorporated into a functional fatigue protocol and compared to

isokinetic fatigue protocols through the measurement of time to stabilization.














CHAPTER 3
METHODS

Subjects

Twenty subjects were asked to voluntarily participate in this investigation. To be

included in this study subjects were between 18 and 30 years of age, and have no prior

history of lower extremity or head injury within the past year. Subjects were excluded if

they suffered from any disorders that affect neuromuscular control and were moderately

trained. (i.e., exercise 2-4 times per week) All subjects were asked to read a description

of the study and sign an informed consent form, approved by the university Institutional

Review Board (IRB) (Appendix A).

Instrumentation

Medical Eligibility Form

The eligibility form (Appendix B) was designed to determine eligibility for

participation in this study. The questionnaire was completed prior to any data collection.

Vertical Jump Station

A Vertec vertical jump device (Sports Imports, Columbus, OH) was used to

establish subjects' maximal vertical jump (Figure 3-1). All subjects will stand next to the

Vertec device and reach as high as possible. This measure was recorded as the subject's

standing height. Subjects will then be asked to jump as high as possible and move the

highest vane possible. This height was recorded as the maximal vertical jump height.

All vanes are measured off at 1.27 cm increments.









Isokinetic Dynamometer

A Kinetic Communicator (Kin Com) 125 AP (Chattanooga Group, Chattanooga,

TN) isokinetic dynamometer integrated with a computer and appropriate software was

used to induce isokinetic fatigue of the plantar and dorsi flexors of the ankle (Figure 3-2).

Triaxial Force Plate

A Bertec triaxial force plate as seen in figure 3-3 (Bertec Corporation, Columbus,

OH) was used to measure duration of instability from time of impact until pretest values

of stability are recorded at a frequency of 600-Hz. The force plate data will undergo an

analog to digital conversion and was stored on a PC-type computer using the DATAPAC

2000 (Run Technologies, Laguna Hills, CA) analog data acquisition, processing, and

analysis system.

Infrared Timing Device

A Brower infrared timing device (Brower Timing Systems, Salt Lake City, UT)

was used to time subjects during the functional fatigue protocol. The device transmitters

(Figure 3-4) project an infrared beam at the start and finish line of the functional fatigue

protocol area. A subject's time began as they crossed and ended as the subject crossed

the finish line. The device was used to determine 150% of initial time for each subject.

Motion Analysis System

Kinematic data was collected using a set of two JVC low speed motion recorder

cameras (US JVC Corporation, Fairfield, NJ) as seen in figure 3-5. This system collects

all data at 60Hz from two angles, both posterior lateral and anterior lateral for all trials.

A motion analysis will allow additional dependent variables of lower extremity joint

angles to be measured using Peak Motus motion analysis system (Peak Performance

Technologies, Englewood, CO) to digitize all kinematic data.

























Figure 3-1. Vertec jump station.


Figure 3-2. Isokinetic dynamometer with integrated computer.


Figure 3-3. Bertec triaxial forceplate.






















Figure 3-4. Brower infrared timing device as set up for the functional fatigue protocol.















Figure 3-5. JVC low speed motion recorder camera.









Measurements

Time to Stabilization

Subjects will start in a standing position 70 cm from the center of the triaxial force

plate. Each subject was required to jump off of both legs and touch a designated marker

placed at a position equivalent to 50% of the subject's maximum vertical leap before

landing on the force plate52 The subject is to land on their stance leg (leg used to plant

when kicking a ball), stabilize as quickly as possible and balance for 20 seconds on the

triaxial force plate. This protocol can be seen in figure 3-6 below moving from right to

left.

The average of the three trials were taken as their respective pretest data score. All

subjects were instructed to jump with their head up and hands in a position to touch the

designated marker. Medial/lateral and anterior/posterior stabilization time was

determined using the technique of sequential estimation (Figure 3-7). The technique

incorporates an algorithm to calculate a cumulative average of the data points in a series

by successively adding in 1 point at a time.12 This cumulative average was compared

against the overall series mean, and the series was considered stable when the sequential

average remained within 1A standard deviation of the overall series mean.12 The series

consists of all data points within the first three seconds of touch down.

Vertical TTS was established as the time when the vertical force component reached and

stayed within 5% of the subject's body weight after landing (Figure 3-8).10 A subject's

body weight was established as the average of the variation of the vertical GRF in the

final second of the 20-second data collection period.









Ground Reaction Forces

The anteroposterior, mediolateral, and vertical and the ground reaction moments about
those axes was collected and analyzed at a frequency of 600Hz. The GRFs
measured in Newton's by computer software will accurately depict how hard
or soft an individual lands from a jump. These GRF measurements are then
quantified as an intensity of the landing, expressed as the magnitude of the
peak force divided by the subject's body weight, or units of body weight.
Anteroposterior and mediolateral GRF variations were used as part of the TTS
calculation. The peak vertical ground reaction force intensity was examined
at two points when initial contact with the force plate is made, (F 1l) forefoot
contact and (F2) rearfoot contact within the bimodal curve associated with a
toe-heel landing in the force-time history (Figure 3-9).26

Motion Analysis

Kinematic data was collected using a set of two JVC motion recorder cameras (US

JVC Corporation, Fairfield, NJ). This system collects all data at 60Hz from two angles,

both posterior lateral and anterior lateral for all trials (Figure 3-10). Camera 1 was

positioned 5.05-m to the posterior lateral side for subjects landing on their right foot or

6.68-m to the posterior lateral side for subjects landing on their left foot, while camera 2

was 5.05-m to the posterior lateral side for subjects landing on their right foot or 6.68-m

to the posterior lateral side for subjects landing on their left foot. Both cameras were able

to view all reflective markers during each landing task, thus enabling three-dimensional

analysis. Reflective markers were placed at the greater trochanter, mid thigh, lateral joint

line of the knee, mid shank, lateral malleolus, calcaneous, and head of the fifth metatarsal

(Figure 3-11).57,58 All video data was analyzed using a Peak Motus motion analysis

system (Peak Performance Technologies, Englewood, CO). Ankle flexion was seen as

the vector angle between the A1-A2 segment (5th metatarsal calcaneous) and the B1-B2

segment (knee lateral malleolus). Knee flexion was then measured as the calculated

vector between P1-V-P2. With the greater trochanter as P1, the knee as the fulcrum (V)

and the lateral malleolus as P2. Knee valgum was determined by the difference of the X






29


coordinates of the greater trochanter and knee in the 3D transformed data. The values

were taken at the point just prior to touch down and at all points after touch down. The

greatest displacement of the greater trochanter and knee X coordinates after touchdown

and at jump height marker were used to find the difference.

































Figure 3-6. Jump protocol from right to left. Starting position, mid-jump and finishing
position.




Sequential Estimation


GRF curve Sequential Estimation -- 1/4 std of overall series mean

Figure 3-7. Graphical representation of sequential estimation


.... NEW






31


Vertical TTS


Vertical TTS Body Weight + 5% Body Weight
Figure 3-8. Vertical time to stabilization analysis method.


SF2

7 / '



F1 /







0.000 20 000 40.000 60 000 80 000 100 000 120 000 140 000 160 000 180 000

Figure 3-9. Force time history curve with GRF collection points highlighted.








Force plate & starting position


Ia


JVC Motion Recorders


Figure 3-10. Camera setup for motion analysis of joint kinematics.


Figure 3-11. Placement of reflective markers.


b


7\











Isokinetic Fatigue Protocol

The isokinetic fatigue protocol was administered using the Kincom Isokinetic

Dynamometer in the Biomechanics Laboratory (Figure 3-12). Subjects were positioned

according to manufacturers specifications for ankle dorsi and plantar flexion (DF and

PF). Each subject will perform 3 sub-maximal and 3 maximal repetitions for a warm-up,

followed by 1 minute of rest. An initial peak torque value will then be taken using the

overlay mode from the 3 maximal repetitions of DF and PF at 120 and 30 degrees per

second respectively.12 The subject will then continue to give a maximal effort with a

continuous series of concentric contractions of DF and PF until PF falls below 50% of

both the respective peak torque values for a minimum of 3 consecutive repetitions.

Functional Fatigue Protocol

Before the functional fatigue protocol is administered each subject was given

instructions and practices and a single maximal effort run of the course for a warm-up,

followed by 1 minute of rest. The functional fatigue protocol, will consist of the

following:

The SEMO Agility Drill

A series of forward sprints, diagonal back-pedaling, and side stepping within a 12'

x 12' area (Figure 3-13). (The subject completed 3 repetitions)

Plyometric Box Jumps

A series of 3 boxes of increasing height, 18" apart (Figure 3-14). The subject must

jump onto the first box, stabilize and jump down, immediately jumping back up onto the

second box, stabilize and repeat onto the third box. (The subject completed 3 repetitions)









Two-legged Hop Sequence

A series of markers spaced over a ten foot distance, were jumped onto and

immediately off of towards the next marker. The subject must jump and land using both

feet for each marker (Figure 3-15).59 (The subject completed 3 repetitions)

Side-to-side Bounds

An area 5' wide in which the athlete must jump sideways from the center marker to

the one side back to the center and then to the opposite side (Figure 3-16). (The subject

completed 30 repetitions)

Mini-tramp

Subjects must jump onto a mini-tramp, stabilize and jump off onto the floor on the

opposite side (Figure 3-17). (The subject completed 30 repetitions)

Co-contraction Arc

Subjects must resist the tension of an elastic cord as the side shuffle around a 180-

degree arc (Figure 3-18).59'60 (The subject completed 10 repetitions)

Fatigue was quantified as the time that it takes for a 150% increase from their

maximal effort run through the course. Time to complete the functional fatigue protocol

was measured using infrared sensors that indicate the time for the completion of each

circuit. Fatigue has been set at 150% to mimic previous studies on the effects of fatigue

on time to stabilization in the literature.19






























Figure 3-12. Subject position for isokinetic fatigue protocol


Figure 3-13. SEMO agility drill.

























Figure 3-14. Plyometric box jumps.


Figure 3-15. Two-legged hop sequence


Figure 3-16. Side-to-side bounds.


























Figure 3-17. Mini-tramp jumps.


Figure 3-18. Co-contraction arc drill.











Procedure

Each subject will report to the biomechanics laboratory on two separate occasions.

On each occasion subjects were pretested for time to stabilization following a single leg

landing on a force plate. Each subject will complete either a functional or an isokinetic

fatigue protocol immediately following the pre-test. Fatigue protocol completion was

randomized counterbalanced. Once fatigue has been induced, each subject was

reassessed for time to stabilization following procedures identical to those used during

protesting.

Additionally a motion analysis of each subject's landing technique was conducted

for all pre and posttest trials. This analysis, based on the average of the three trials

completed, will compare and contrast the average amount of ankle and knee flexion and

knee valgum from the two fatigue protocols.

Post testing procedures were initiated 30 seconds following completion of the

fatigue protocol. When subjects return on the second occasion the same procedures were

followed, however, a different fatigue protocol was used. The ordering of the fatigue

protocols were in a randomized counter balanced order with a minimum of one week

separating testing sessions.

Data Analysis

The independent variables are the fatigue protocols and test, while the dependent

variables will consist of time to stabilization, vertical GRF, and knee and ankle angles.

The data was analyzed with two-way analyses of variance (ANOVA) with repeated

measures. The two within subject variables will include fatigue protocol (isokinetic vs

functional) and time (pre-test vs. post test). The means were compared between all






39


conditions, to determine the main effects of protocol and time. Following the analysis,

post hoc testing was conducted using a Tukey's HSD test. A Pearson Product Moment

Correlation Coefficient was calculated to determine if a relationship exists between the

ground reaction forces, time to stabilization, and knee and ankle angles. An alpha level

was set at .05 for all statistical analyses.














CHAPTER 4
RESULTS

Introduction

The purpose of this study was to compare the effects of isokinetic and functional

fatigue on TTS, peak vertical ground reaction forces and joint angles during a single-leg

jump landing. The isokinetic fatigue protocol was adapted from those commonly

reported in the literature while the functional fatigue protocol was developed to simulate

actual athletic practice and game situations. The independent variables included the

fatigue protocol (isokinetic vs functional) and time (pre- vs post-exercise). The

dependent measures included vertical, medial/lateral, anterior/posterior time to

stabilization scores, peak vertical ground reaction forces (toe strike, heel strike),

maximum ankle, and knee flexion, and maximum knee valgum. Data were analyzed to

identify differences among any of these measures and are presented according to the

dependent measure that they represent. Raw data and ANOVA tables are found in

Appendices D and E.

Subjects

Twenty healthy subjects free from lower extremity injury, CNS injury and

disorders that affect neuromuscular control over the past six months. All subjects read a

description of the study and signed an informed consent form, approved by the university

Institutional Review Board (IRB) (Appendix A). Subject's averaged 221.6 years of age,

were 173.8410.452 cm in height, and 67.1312.426 kg in weight.









Time to Stabilization

Vertical

The group means and standard deviations for vertical TTS can be found in Table 4-

1. The times ranged from 206.71- to 385.63-ms during pre-testing and from 200.60- to

1175.59-ms during post testing. No significant protocol [F(1,19)=4.96, p=.490] or time

[F(1,19)=.000, p=.986] main effects were observed. Likewise, no significant protocol by

time interaction [F(1,19)= 3.93, p=.538] was observed for vertical TTS.

Table 4-1. Vertical TTS as determined by vertical GRF-Fz (mean SD)
Combined
Fatigue Protocol Pre-exercise (ms) Post exercise (ms) Protocol (ins)
Protocol (ms)
Isokinetic 290.42 +42.21 286.15 47.88 288.2944.06
Functional 278.03 52.95 281.85 62.85 279.57758.26
Combined Time 284.2347.68 283.6456.12


Medial/Lateral

The group means and standard deviations for medial/lateral TTS can be found in

Table 4-2. The times ranged from 53.34- to 2232.11-ms during pre-testing and from

997.98- to 2219.33-ms during post testing. No significant protocol [F(1,19)=.388,

p=.541] or time [F(1,19)=.434, p=.518] main effects were observed. Likewise, no

significant protocol by time interaction [F(1,19)= .287, p=.598] was observed for

medial/lateral TTS.

Table 4-2. Medial/Lateral TTS as determined by GRF-Mx (mean SD)
Combined
Fatigue Protocol Pre-exercise (ms) Post exercise (ms) Protocol (ins)
Protocol (ms)
Isokinetic 676.57 615.78 350.90 445.51 1491.137493.49
Functional 523.29464.95 533.66 594.12 911.31+694.01
Combined Time 912.69710.89 1489.76470.58









Anterior/Posterior

The group means and standard deviations for anterior/posterior TTS can be found

in Table 4-3. Times ranged from 796.27- to 2136.538-ms during pre-testing and from

11.67- to 2053.19-ms during post testing. Significant protocol [F(1,19)=8.93, p=.009]

and time [F(1,19)=7.72, p=.012] main effects were observed for anterior/posterior TTS.

A significantly greater TTS was observed during the pre-test time session (1559.35

344.74 ms) as compared to post-test session (1322.92 +427.01 ms) and the functional

protocol session (1320.92 +417.94 ms) TTS was significantly shorter than the isokinetic

protocol session (1440.20 475.24 ms). However, these significant main effects were not

associated with a significant protocol by time interaction [F(1,19)= .001, p=.978].

Table 4-3. Anterior/Posterior TTS as determined by GRF-My (mean SD)
Combined Protocol
Fatigue Protocol Pre-exercise (ms) Post exercise (ms) ( s)
(ms)
Isokinetic 1444.40323.38 1201.43470.59 1320.92417.94
Functional 1678.97335.21 1201.43470.59 1440.20475.24#
Combined Time 1559.35344.74 1201.43476.59*
* Significantly > Pre-exercise, p<.05
# Significantly > Isokinetic, p<.05

Ground Reaction Forces

The group means and standard deviations for peak vertical ground reaction forces

can be found in Table 4-4 and 4-5. The ground reaction forces were analyzed at two

different points in the ground reaction curve, at toe strike (F 1l) and at the heel strike (F2).

The Fl ground reaction force scores ranged from 389.054- to 1768.49-N, while the F2

ground reaction force scores ranged from 1308.20- to 3748.18-N.

A significant time main effect [F(1,19)=8.64, p=.008] was observed for the ground

reaction force at heel strike, as the post test (2772.57 590.10 N) ground reaction force









was significantly greater than the pre-test (2651.78 588.50 N). However, this was not

observed at toe strike, as the time main effect was not significant [F(1,19)= 1.44, p=.246].

Significant protocol main effects were not observed for either heel strike [F(1,19)=.80,

p=.383] or toe strike [F(1,19)=.46, p=.507]. Likewise, significant protocol by time

interactions were not observed for heel strike [F(1,19)=.37, p=.070] or toe strike

[F(1,19)=.121, p=.286].

Table 4-4. Toe Strike-Fl as determined by GRF-Fz (mean SD)
Post exercise Combined
Fatigue Protocol Pre-exercise (Newtons) (Newtons) Protocol (N)
(Newtons) Protocol (N)
Isokinetic 1149.402234.523 1178.551166.41 1163.58207.59
Functional 1103.671321.225 1137.197280.255 1120.43305.05
Combined Time 1125.95286.96 1156.79273.41

Table 4-5. Heel Strike-F2 as determined by GRF-Fz (mean SD)
Post exercise Combined
Fatigue Protocol Pre-exercise (Newtons) (Newtons) Protocol (N)
(Newtons) Protocol (N)
Isokinetic 2572.752572.042 2783.463623.38 1987.38957.44
Functional 2730.814579.321 2761.685538.683 2746.25566.71
Combined Time 1960.38919.45 2772.57590.10*
* Significantly > Pre-exercise, p<.05

Joints Kinematics

In this study three aspects of joint kinematics were measured during the dynamic

stability protocol. These measurements included a maximum ankle and knee flexion

during the jump landing and the maximal knee valgum that occurred as a result of that

landing.

Dorsiflexion

The group means and standard deviations can be found in Table 4-6. The

maximum ankle flexion scores ranged from 53.42 to 91.400 at pre-test and from 55.760









to 94.44 at post test. No significant protocol [F(1,19)=.94, p=.344] or time [F(1,19)=.02,

p=.905] main effects were observed. Likewise, no significant protocol by time

interaction [F(1,19)= .06, p=.803] was observed for maximum ankle flexion.

Table 4-6. Ankle Flexion (mean SD)
Post exercise Combined
Fatigue Protocol Pre-exercise (degrees) (degrees) Protocol (degrees)
(degrees) Protocol (degrees)
Isokinetic 71.910.2 71.79.5 72.69.2
Functional 69.37.8 69.38.9 69.8+8.1
Combined Time 71.28.7 71.28.8

Knee Flexion

The group means and standard deviations can be found in Table 4-7. The

maximum ankle flexion scores ranged from 111.110 to 145.94 at pre-test and from

114.00 to 143.110 at post test. No significant protocol [F(1,19)=.67, p=.425] or time

[F(1,19)=.58, p=.456] main effects were observed. Likewise, no significant protocol by

time interaction [F(1,19)= .21, p=.652] was observed for maximum knee flexion.

Table 4-7. Knee Flexion (mean SD)
Post exercise Combine Protocol
Fatigue Protocol Pre-exercise (degrees) (degrees) (degrees)
(degrees) (degrees)
Isokinetic 129.79.3 128.88.0 129.88.9
Functional 128.39.3 128.07.5 128.28.6
Combined Time 129.39.3 128.77.7


Knee Valgum

The group means and standard deviations can be found in Table 4-8. The

maximum knee valgum scores ranged from -.009cm to .09cm at pre-test and from -

.008cm to .084cm at post test. No significant protocol [F(1,19)=.07, p=.796] or time









[F(1,19)=.12, p=.737] main effects were observed. Likewise, no significant protocol by

time interaction [F(1,19)= .79, p=.386] was observed for maximum knee valgum.

Table 4-8. Knee Valgum (mean SD)
Combined
Fatigue Protocol Pre-exercise (M) Post exercise (M) Protocol (M)
Protocol (M)
Isokinetic 0.030.03 0.030.03 0.030.02
Functional 0.030.02 0.030.02 0.030.02
Combined Time 0.030.02 0.030.02

Correlational Analysis

A Pearson product moment correlation was run on the pretest measures of all

dependent variables, to determine if interdependence existed between the dependent

variables. Through the analysis several significant correlations were noted. Vertical time

to stabilization had significant correlations to GRF-F1 (r=.534, p<.001), maximum ankle

flexion (r=-.445, p=.004), and maximum knee flexion (r=-.667, p<.001). The other TTS

measures, medial/lateral, and anterior/posterior only had a significant correlation with

GRF-F2 (r=-.775, p=.001) and (r=.401, p=.011). In addition to the significant correlation

that GRF-F 1 had with vertical TTS, a significant correlation was also noted with maximal

knee flexion (r=--.385, p=.015). Maximal ankle flexion also had an additional significant

correlation with maximal knee flexion (r=.533, p=.001). There were no significant

correlations found for knee valgum scores. A complete table of the Pearson product

moment correlation coefficients can be seen in Table 4-9.










Table 4-9. Pearson Product Moment Correlation (r and significance)
Pearson product moment correlation coefficients
Vertical Med/Lat Ant/Pos GRF-F1 GRF-F2 Ankle Knee Valgum

Vertical r 1 .173 .145 .534* .158 -.445* -.667* -.208
Sig. .284 .373 .001 .336 .004 .004 .198
Med/Lat r .173 1 -.267 .116 -.775* .182 .011 -.027
Sig. .284 .095 .483 .001 .262 .946 .866
Ant/Pos r .145 -.267 1 .128 .401* -.179 -.309 .131
Sig .373 .095 .438 .011 .268 .053 .420
GRF-F1 r .534* .116 .128 1 .222 -.230 -.385* -.137
Sig .001 .483 .438 .175 .159 .015 .405
GRF-F2 r .158 -.775* .401* .222 1 -.201 -.297 -.104
Sig .336 .001 .011 .175 .221 .066 .528
Ankle r -.445* .182 -.179 -.230 -.201 1 .533* .077
Sig .004 .262 .268 .159 .221 .001 .637
Knee r -.667* .011 -.309 -.385* -.297 .533* 1 -.031
Sig .004 .946 .053 .015 .066 .001 .852
Valgum r -.208 -.027 .131 -.137 -.104 .077 -.031 1
Sig .198 .866 .420 .405 .528 .637 .852
* Correlation is significant at the .05 level (2-tailed)














CHAPTER 5
DISCUSSION

The purpose of this study was to compare the effects of isokinetically and

functionally induced fatigue on time to stabilization (TTS), peak vertical ground reaction

forces and joint kinematics (i.e., ankle and knee flexion and knee valgum) during a

single-leg landing stabilization test. Three hypotheses were examined and are discussed

below. The first hypothesis stated that there would be significant increases in time to

stabilization, peak vertical ground reaction forces, and joint kinematics in the post test

measures as compared to the pretest measures. The second hypothesis stated that a

greater change in the dependent variables would be noted following functional fatigue as

compared to isokinetic fatigue. The results of this study failed to support either of these

hypotheses. The third hypothesis stated that there would be a high correlation between

peak vertical ground reaction forces and time to stabilization when assessed in an

unfatigued state. In general, there was a low to moderate relationship to support the third

hypothesis.

Fatigue

The primary purpose of this study was do determine if functionally induced fatigue

would have a greater effect on TTS and joint kinematics as compared to isokinetically

induced fatigue. However, no differences were observed when comparing the two

fatigue protocols. It is difficult to make comparisons between the two types of exercise,

as neither protocol had an effect on these variables. This conflicts with the results of

previous studies assessing the influence of fatigue on neuromuscular control.9'16'17'19









Johnston et al.9 and Douex et al.19 reported that both isokinetic and functional fatigue

protocols respectively, significantly increased postural sway as subjects stood on an

unstable platform. Likewise, Yaggie and McGregor16 and Joyce et al.17 induced fatigue

in the dorsi and plantar flexors using an isokinetic protocol and observed a significant

increase in postural sway during a unilateral balance task. Yaggie and McGregor16

observed this difference with an eccentric/concentric mode at 600 per second while

additionally running the protocol on inversion/eversion motions. Joyce et al.17 utilized

the same isokinetic fatigue protocol that was used in this study, but conducted that

protocol in a prone position. It is important to note that none of the above studies used

TTS as a measure of neuromuscular control or stability. Thus, it is difficult to make

comparisons with our study. It is possible that we might have observed changes has

similar testing protocols been used.

It is possible that the isokinetic and functional exercise protocols used in the

present investigation did not sufficiently fatigue the musculature of the lower leg. If they

had been sufficient, differences in TTS, GRF, or joint kinematics would be expected. No

one definition of fatigue exists in the literature, as fatigue can occur at numerous points in

the neuromuscular pathway. For the present investigation, isokinetic fatigue was defined

as the point at which a subject could not produce 50% of their respective plantar and

dorsiflexion peak torque at the respective speeds of 30 and 1200 per second in a

concentric/concentric mode. This specific protocol has been used previously, by

Johnston et al.9 and Joyce et al.17 who as stated earlier determined that isokinetic fatigue

protocols effect postural sway. The increased postural sway observed in those studies

suggests that the lower leg musculature was sufficiently fatigued. Thus, changes in our









dependent measures would be expected as well. These isokinetic protocols directly

fatigue the plantar flexors, which are the main stabilizing muscles for balancing over an

extended period of time.3'4'25 However, during the time to stabilization, the single leg-

hop protocol vertical TTS scores averaged less than .05-sec, while the medial/lateral and

anterior/posterior scores were typically less than 3-sec. When landing from a forward

jump, momentum brings the center of gravity forward over the stationary foot. Thus,

dorsiflexion occurs at the ankle or anterior sway. When this occurs, the plantar flexors

are stimulated via the stretch reflex to return the body to a stable position. The triceps

surae muscle group, reported as the main stabilizers for balance, would then play a vital

role in the initial phase of landing that the single leg hop protocol reproduces. If this

theory is correct, then an isokinetic fatigue protocol should have an effect on TTS scores

and reinforces the assumption that the isokinetic fatigue protocol used was not sufficient

to fatigue the lower leg musculature.

Douex et al.19 used a functional protocol, fatiguing the subject anaerobically

through a series of 40-yard sprints. We defined functional fatigue as the point at which a

subject could not complete the exercise protocol in less than 150% of their initial time.

Muscular fatigue induced in similarly in isokinetic protocols have been shown to last up

to 90 seconds post fatigue.11 While the functional fatigue protocol has not been used

previously in the literature, there were anecdotal reports of delayed onset muscle soreness

following testing. Unlike the isokinetic protocol, this type of exercise involved knee, hip,

and upper extremity musculature. This protocol was designed to incorporate, various

aspects of athletic competition, including agility, quick explosive movements, muscular

endurance, and aerobic capacity. Agility and balance in the two leg hop sequence and









agility drill. Quick explosive movements in the plyometric box jump. Muscular

endurance and aerobic capacity of the lower extremity musculature and the

cardiopulmonary system were respectively stressed through the series of side-to-side

bounds, mini-tramp jumps and co-contraction arcs. Aerobic capacity was also

incorporated in the overall time to completion of the fatigue protocol. On average time to

complete one circuit was approximately 5 minutes, with most subjects performing 3-4

circuits before fatigue. It is possible that the increases in time to perform the protocol

were due to reduced effort as opposed to actual fatigue. However, it is possible that our

functional fatigue protocol was not comprehensive enough to fatigue the lower extremity

musculature or not specific enough to fatigue the necessary lower extremity musculature

to indicate a difference in TTS scores. Similarly, the opposite could be true, the

functional fatigue protocol could have been too effective. Decreasing the subjects

neuromuscular control to a level where they could not complete the jump protocol until

after fatigue had decreased.

Jump Landing Protocol

Several jump-landing protocols have been used in previous studies to measure

postural sway. Forward and lateral step down tests as well as single leg hop tests have all

indicated significant effects of fatigue on stabilization time12'18 52. It is possible that our

failure to observe changes following fatigue was due to trial mortality and difficulty

during the performance of the jump landing tests. It could be reasoned that the jump

protocol may be too difficult or not specific enough to determine differences between

healthy subjects.

Few studies have used TTS as a measure of stability or neuromuscular control;

however, only one of these studies has examined the effects of fatigue. Previous studies









have compared healthy and injured subjects12'52. The results from these studies suggest

that subjects with functionally unstable ankles52 and subjects with ACL deficiencies12

experience longer times to stabilization than healthy subjects. Maggio et al.18 examined

the effects of evertor muscle fatigue on dynamic stabilization time. In that study, healthy

and functionally unstable ankles were assessed during a forward and lateral step down

test protocol. The results indicated a significant difference in FUA subjects, but no

difference in healthy subjects. We only used healthy subjects in the present investigation.

Thus, our results are in agreement with those involving the healthy subjects assessed in

the above-mentioned study.

Due to the trial mortality and the subjects' inability to land in a balanced state, a

greater variation in the time to stabilization scores was seen. These variations would

directly effect the medial/lateral and anterior/posterior TTS scores as the subjects tried to

regain balance after landing. Concurrent with the results of Maggio et al.18, data from

this study illustrate a performance improvement in time to stabilization scores post

fatigue in healthy subjects. Also noted were the high scores on both TTS measures

during the functional fatigue protocol, despite the lack of significance found. These

variations in landing as a result of the complicated landing task may also indirectly effect

the vertical TTS scores. This illustrates the minor trend occurring towards an interaction

for vertical time to stabilization as well as the trend towards a main effect between

fatigue protocols.

Despite the variations, which would have been noted across the pre and posttest

trials, the trial mortality, might have affected the posttest sessions more severely. While

the post test trials were initiated 30 seconds after completion of the respective fatigue









protocols, the completion of the post test data collection took much longer than

anticipated. This delay in data collection might have allowed some degree, if not

complete, recovery of the fatigued muscles. This recovery would reduce deficits in

proprioceptive awareness and muscular force, potentially increasing the subjects'

neuromuscular control for the post-test sessions. The delay in data collection may also

explain why some TTS scores were lower during post fatigue testing respective to the pre

fatigue scores. This trend was concurrent with Maggio et al.18 who also indicated that the

scores of healthy subjects tended to improve during the post-test trials. If due to the trial

mortality and delay in collection, subjects' proprioceptive feedback and muscular

strength returned to normal, then the lower post-test scores can be explained by a learning

effect.

Validity of Measure

It is also possible that TTS is not the best test to measure the effects of fatigue on

neuromuscular control. Reliable methods commonly reported in the literature include

single-leg-stance both on a force plate and unstable platform and the star excursion

balance test.9'13'16 These measures may be more sensitive to variations in ground reaction

forces or center of pressure changes resulting from lower extremity muscle fatigue. This

rationale forces a look at the assumption that the subject effort would be maximal. If

subject effort was not maximal during the fatigue protocols, then the post-test scores are

not true indicators of how fatigue would affect the said dependent variables.

Furthermore, if subject effort was not full during the testing protocol, then the scores of

the dependent variables are not accurate or true representations of the changes to them

due to fatigue.










Ground Reaction Forces

This study did find significance for the peak vertical ground reaction forces at the

heel strike (F2). This finding indicates that as fatigue of the lower extremity musculature

increases, the body's ability to absorb the shock of a landing decreases, despite the lack

of significance found in the other measures taken. This is due to the triceps surae muscle

groups losing the ability to eccentrically decelerate the body from a jump landing. This

inability to control deceleration creates a more unimodal or flat-foot landing style which

could potentially increases the chances of ankle injury. These findings are concurrent

with those of 10,24,55 whose studies also indicated an increase in GRFs due to fatigue. In

Figure 5-1, the trend for the peak vertical ground reaction forces at point F2 can be seen.

These charts illustrate that a trend did occur toward an interaction of test and protocol at

the F2 collection point. Both these points, (F 1l, F2) in the ground reaction force history

curve were also moderately correlated to the vertical TTS and medial/lateral as well as

anterior/posterior TTS scores respectively.


6000 -

5000 -

4000 -
S-*-- functional
3000 -
W3000 --- -J -0- isokinetic
2000 -

1000 -

0
Pre to Post

Figure 5-1. Peak vertical GRF at heel strike (F2).









Joint Kinematics

In this study, aspects of joint kinematics were measured during the dynamic

stability protocol: including maximum ankle and knee flexion during the jump landing

and the maximal knee valgum that occurred as a result of that landing. There were no

significant differences found in any kinematic measurement as a result of this study.

However, a moderate negative correlation between maximal dorsi and knee flexion

was found with vertical time to stabilization. This indicates that the less flexion of the

said joint angle would indicate a greater vertical TTS score.

Correlation

The results of this study indicate that there is a moderate relationship between

vertical TTS and GRF-Fl, as well as for anterior/posterior TTS and GRF-F2. A high

correlation was found between medial/lateral TTS and GRF-F2. These results help

illustrate that the measure of time to stabilization is in part determined by the force by

which a subject lands for the jump protocol. This analysis also indicates that the higher a

person's force at toe touch, the higher their vertical time to stabilization will be; while the

force at heel strike is positively correlated to anterior/posterior TTS, the less force at heel

strike the smaller the anterior/posterior TTS score will be. Force at heel strike was

negatively correlated to medial/lateral TTS, indicating that the less force at heel strike,

the greater the medial/lateral TTS score will increase.

Indications

The results of this study indicate that there is no difference between the effects of

an isokinetic and a functional fatigue protocol of the lower leg and that there was no

difference between the TTS, GRF, and joint kinematic scores prior to and after fatigue.

These finding are contrary to previous studies that indicated that both isokinetic and









functional fatigue protocols have significantly increased postural sway.9'16-19 This study

may however indicate that an isokinetic fatigue protocol could potentially be a valid and

acceptable method to study the effects of fatigue. This would allow for faster, safer and

more reproducible testing of subjects in an effort to better understand the effects of

fatigue on neuromuscular control.

However, until a definitive and direct answer of whether or not an isokinetic or

functional fatigue protocol is the best means to study fatigue's effect on neuromuscular

control and postural sway can be made, comparative studies should be the basis for future

research. It is also important that athletic trainers, coaches, therapists, and physicians

continue to train their athletes in ways that will increase their proprioception and

minimize any loss of neuromuscular control due to the fatigue of athletic competition

until the exact cause of proprioceptive deficits and loss of neuromuscular control can be

established.

Conclusions

The following conclusions are made as a result of this study:

* There was no difference in time to stabilization scores prior to and after an isokinetic
and functional fatigue protocol of the lower extremity musculature.

* There was no difference between the effects of an isokinetic fatigue protocol on TTS,
GRF and joint kinematics as compared to a functional fatigue protocol.

* There was a moderate correlation between vertical time to stabilization and maximal
ankle and knee flexion. There was also a high correlation between GRF-F2 and
medial/lateral time to stabilization.

Summary

The results of this study indicate that there is no difference between the effects of

an isokinetic and a functional fatigue protocol on TTS, GRF, and joint kinematics. The









results also indicate that there is a small to moderate correlation between several of the

dependent variables.

While muscle fatigue has been shown to increase postural sway and vertical GRF

in several studies, by incorporating isokinetic and or functional fatigue protocols, the

results of this study indicate there no relationship between increases in fatigue and

increases in time to stabilization. However, the results of this study do indicate that

fatigue does increase the vertical GRF seen at heel strike. This increase has been

associated with an increased latency period and altered joint kinematics in jump

landing.10,24,55 Two possible indicators of increases incidence of injury at the ankle.

These results benefit researchers indicating that an isokinetic fatigue protocol is a

reliable method of mimicking the fatigue that takes place during athletic activity.

Until a definitive answer to the question of why the ankle is the most commonly

injured structure in the body, and fatigue plays a role, athletic trainers, therapists,

physicians, and coaches should encourage athletes to focus on improving their

proprioceptive awareness and proper technique in landing from jumps. Improving

proprioception and learning proper landing techniques may help in reducing an athlete's

chances of suffering an ankle injury.

Implications for Future Research

This study has generated several new questions in which future researchers can

explore. This study tested healthy subjects who had no previous history of lower

extremity injury. Future research should examine subjects with previous injuries,

including those with functional and anatomical ankle instability. The current study used

a fatigue protocol that used 50% of peak torque and initial time as the standard for

fatigue. Future research should be conducted with various levels of fatigue as a









percentage of peak torque for an isokinetic protocol and initial time for a functional

fatigue protocol. Future research should also examine further comparative studies of

isokinetic and functional fatigue protocols measuring their effects with more tested and

reliable measures of postural sway.

In addition, future research should look to determine the learning effect associated

with the time to stabilization single leg hop protocol, it's reliability and validity and the

various methods of calculating it. Comparisons of a control and treatment group would

add to the general body of knowledge and indicate the amount of practice needed to

minimize the learning effect for this protocol. If valid and reliable, future studies should

examine the differences in time to stabilization between males and females. Other

research endeavors should explore the effect of various sensory deprivation on time to

stabilization and more importantly the changes in postural sway and time to stabilization

over the course of actual athletic practice and games in varying sports. Also, future

research should include a prospective study to determine if time to stabilization is a

predictor of the incidence of ankle injuries in the sports where jump landing is prevalent,

such as basketball, soccer, and volleyball.














APPENDIX A
LETTER OF INFORMED CONSENT

Informed Consent Agreement
Project Title: Effects of isokinetic vs. functional fatigue protocol of the lower extremity
on time to stabilization and peak vertical ground reaction forces.


Investigators: Erik A Wikstrom,ATC, Graduate Student, Department of Exercise and
Sport Sciences & Michael E. Powers, PhD., ATC, CSCS, Assisstant Professor,
Department of Exercise and Sport Sciences.

Purpose of the study: The purpose of this study is to compare and correlate the effects of
two different methods of tiring out the lower leg, by measuring the required time to
regain your balance and how much force you produce from landing during a single-leg-
hop balance test. This study will also examine the amount of flexion or bend that occurs
in the ankle and knee from the fatigued landing during the single-leg-hop balance test.

Please read this consent carefully before you decide to participate in this study.


What will you do in this study?
Upon reporting to the Athletic Training/Sports Medicine Research Laboratory (105D
FLG), you will be asked to complete the medical history form to determine if you are
eligible to participate in the study. If eligible, your maximum vertical leap (how high you
can jump) will be determined. To do this, we will first measure how high you can reach
while standing. You will then be asked to jump as high as possible and touch markers
supported on a stand. Based on the number of markers you touch, the height of your
jump is determined. We will have you do this two more times to asure that we get an
accurate measure. Immediately following the jump test, we will place reflective markers
on the outside of your ankles, knees, hips, and shoulders using tape. We will then
measure how long it takes you to balance after jumping onto a platform. You will be
asked to jump so that you reach a height equivalent to half of your maximum jump height
and land on a platform 28" away. After you land on the platform you will be asked to
balance yourself on one leg while your hands remain on your hips for a period of 20
seconds. You will be video taped while you do this. The video tape and the reflective
markers will allow us to determine how well you balance. After the 20-second period
you will be asked to return to the starting position and repeat the measurement. This will
be done one more time for a total of three trials. After the balance measurements are
completed, we will attempt to fatigue (tire out) your lower leg muscles using one of two
methods. Which method you do first will be randomly determined by a coin toss.









One of the fatigue protocols will require you to sit in a chair in a machine that will
fatigue your muscles by providing maximum resistance at a set speed of movement as
you bring and point the foot and toes upward and then point the foot and toes downward.
You will warm up and determine your strongest movement and after a minute of rest
proceed with the test by continuously repeated the above motions of the ankle until
fatigue, which will be 50% of your strongest movement as determined by the computer
on the machine.
The other fatigue protocol will requrie you to complete a series of timed sprinting, cutting
and jumping stations. You will first warm up and received instructions. After a minute
of rest you will start by running through a timing marker and then complete the stations
in order until the series is complete. After each series of stations you must run back
through the timing marker. You will be asked to continue performing the stations until a
series takes you 1 /2 times as long as the first series (50% longer than the first series).
The stations in each series will consist of the following;
Agility drill- A series of forward sprints, diagonal back-pedaling, and side stepping
within a 12' x 12' area. (3 times)
Box jumping- A drill that mimics the rapid jumping and landing that would be
experienced in athletic competition. This drill is a series of 3 boxes of 24" in height 18"
apart. You will jump onto the first box, stabilize and jump down, immediately jumping
back up onto the second box, stabilize and repeat onto the third box. (3 times)
Two-legged hop sequence- A series of markers spaced over a ten foot distance, must be
jumped onto and immediately left for the next marker. You need to jump and land using
both feet for each marker. (3 times)
Side-to-side bounds- An area 5' wide in which you will jump sideways from a center
marker to the one side and back to the center to the opposite side. (30 times)
Mini-tramp- You will be ased to jump onto a mini-trampoline, stabilize and jump off
onto the floor on the opposite side. (30 times)
Resistance arc- You will be asked to resist the tension of an elastic cord as you side
shuffle around semi circle. (10 times)

Immediatley after you are done with the fatigue protocol you will be asked to return to
the laboratory and complete another balance test identical to the one completed before the
fatigue protocol. Once this is completed the session will be over. You will be asked to
return to the laboratory 1 week later to repeat the entire protocol, however, you will
perform the other fatigue protocol (the one you did not perform on the first day).


Time requried:
Two sessions requiring approximately 45 minutes each.


Risks:
As with any type of exercise, there is a slight risk of musculoskeletal injury such as a
sprain or a muscle pull. A certified athletic trainer will be present to evaluate and treat
any such injuries should they occur.









Benefits/Compensation:
There are no direct benefits to you for participating.


Confidentiality:
Data will be kept confidential to the extent provided by the law. Your information will
be assigned a code number. The list connecting your name to this number will be kept in
a locked file. When the study is completed and the data have been analyzed, the list will
be destroyed. Your name will not be used in any report.


Voluntary Participation:
Your participation is completely voluntary. There is no penalty for not participating.


Right to withdraw from the study:
You have the right to withdraw from the study at anytime without penalty.


Who to contact if you have questions about the study:
Erik A Wikstrom, BS, ATC/L Mike Powers, Ph.D., ATC/L,
University of Florida University of Florida
Department of Exercise and Sport Sciences Department of Exercise and Sport Sciences
Graduate Assistant Athletic Trainer 148 Florida Gym
2777 SW Archer Road Apt. R-85 PO Box 118205
Gainesville, FL 32608 Gainesville, FL 32611-8205
372-5592(home) (352) 392-0584, ext. 1332
Fax: (352) 392-5262 Fax: (352) 392-5262
E-mail: gatoratc@hotmail.com E-mail: mpowers@hhp.ufl.edu

Who to contact about your rights in the study:
UFIRB Office
Box 112250, University of Florida
Gainesville FL 32611-2250
(352) 392-0433.


Agreement:
I have read the procedure described above. I voluntarily agree to participate in the
procedure and I have received a copy of this description.


Participant: Date:


Principal Investigator:


Date:















APPENDIX B
MEDICAL ELIGIBILITY QUESTIONNAIRE

1. Name

2. Age

3. Height / Weight

4. What leg would you kick a soccer ball with?

Left Right

5. Have you had a lower extremity injury within the past six months?

Yes No

6. Have you been diagnosed with a concussion within the past six months?

Yes No

7. Have you been diagnosed with an equilibrium disorder?

Yes No

8. Do you have a diagnosed disorder that affects neuromuscular control?

Yes No

9. How often do you exercise?

0-2 times a week 2-4 times a week 4+ times a week


















Subject #
Maximal Vertical Leap_

Isokinetic Protocol

PRE-TEST:
Time to stabilization
GRF-F1
GRF-F2
Ankle Flexion
Knee Flexion
Knee Valgus/Verus


Fatigue Protocol
Peak Torque
Fatigue
Actual Percentage


POST-TEST:
Time to stabilization
GRF-F1
GRF-F2
Ankle Flexion
Knee Flexion
Knee Valgus/Verus


APPENDIX C
DATA COLLECTION FORMS


Stance Leg
Jump Height (50%max)


Trial 1


PF
PF
PF


Trial 2


DF
DF
DF


Trial 1


Trial 2


Trial 3


Trial 3









Subject #
Maximal Vertical Leap_

Functional Protocol

PRE-TEST:
Time to stabilization
GRF-F1
GRF-F2
Ankle Flexion
Knee Flexion
Knee Valgus/Verus


Fatigue Protocol
Initial Time
Fatigue
Actual Percentage

POST-TEST:
Time to stabilization
GRF-F1
GRF-F2
Ankle Flexion
Knee Flexion
Knee Valgus/Verus


Stance Leg
Jump Height (50%max)


Trial 1


PF
PF
PF


Trial 2


DF
DF
DF


Trial 1


Trial 2


Trial 3


Trial 3














APPENDIX D
ANOVA TABLES

Tests of within-subjects effects


Table D-1. Vertical TTS ANOVA table
Source Sum of Squares Df Mean Square F Sig.
Protocol 1371.747 1 1371.747 .496 .490
Error(protocol) 52545.726 19 2765.565
Time 41138.323 1 41138.323 2.239 .151
Error(time) 29418.152 19 1548.324
Protocol*Time 337.779 1 337.779 .393 .538
Error(protocol*time) 16342.684 19 860.141




Table D-2. Medial/Lateral TTS ANOVA table
Source Sum of Squares Df Mean Square F Sig.
Protocol 74416.930 1 74416.930 .388 .541
Error(protocol) 3644487.244 19 191815.118
Time 109031.775 1 109031.775 .434 .518
Error(time) 4776494.299 19 251394.437
Protocol*Time 23209.609 1 23209.609 .287 .598
Error(protocol*time) 154370.268 19 80756.330



Table D-3. Anterior/Posterior TTS ANOVA table
Source Sum of Squares Df Mean Square F Sig.
Protocol 1117970.407 1 111970.407 8.529 .009*
Error(protocol) 2490392.677 19 131073.299
Time 1162682.933 1 1162682.933 7.725 .012*
Error(time) 2859804.258 19 150516.014
Protocol*Time 68.859 1 68.859 .001 .978
Error(protocol*time) 1747346.945 19 91965.629
Indicates significance; p<.05









Table D-4. GRF-F1 ANOVA table
Source Sum of Squares Df Mean Square F Sig.
Protocol 21760.031 1 21760.031 .459 .507
Error(protocol) 805763.143 17 47397.832
Time 19669.628 1 19669.628 1.441 .246
Error(time) 232056.582 17 13650.387
Protocol*Time 13237.474 1 13237.474 1.211 .286
Error(protocol*time) 185829.458 17 10931.145



Table D-5. GRF-F2 ANOVA table
Source Sum of Squares Df Mean Square F Sig.
Protocol 92866.586 1 92866.586 .797 .383
Error(protocol) 2213852.009 19 116518.527
Time 291813.119 1 291813.119 8.644 .008*
Error(time) 641402.224 19 33758.012
Protocol*Time 161712.712 1 161712.712 3.673 .070
Error(protocol*time) 836419.613 19 44022.085
Indicates significance; p<.05




Table D-6. Ankle Flexion ANOVA table
Source Sum of Squares Df Mean Square F Sig.
Protocol 125.572 1 125.572 .940 .344
Error(protocol) 2537.431 19 133.549
Time .129 1 .129 .015 .905
Error(time) 167.522 19 8.817
Protocol*Time .409 1 .409 .064 .803
Error(protocol*time) 121.710 19 6.406



Table D-7. Knee Flexion ANOVA table
Source Sum of Squares Df Mean Square F Sig.
Protocol 23.671 1 23.671 .666 .425
Error(protocol) 675.398 19 35.547
Time 6.173 1 6.173 .580 .456
Error(time) 202.287 19 10.647
Protocol*Time 1.710 1 1.710 .209 .652
Error(protocol*time) 155.197 19 8.168









Table D-8. Knee Valgum ANOVA table
Source Sum of Squares Df Mean Square F Sig.
Protocol 4.033E-05 1 4.033E-05 .069 .796
Error(protocol) 1.116E-02 19 5.873E-04
Time 1.296E-05 1 1.296E-05 .116 .737
Error(time) 2.127E-03 19 1.119E-05
Protocol*Time 9.288E-05 1 9.288E-05 .788 .386
Error(protocol*time) 2.239E-03 19 1.178E-04
















APPENDIX E
RAW DATA TABLES


Table E-1. Subj ect Demographics.
Max Jump Peak Peak Units Body
Subject Sex Stance Leg Height Weight Vertical Height Torque PF Torque DF Intial Time Wieght
(cm) (kg) (cm) (cm) newtonss newtonss (min-sec) (volts)
1 femaleleft 170.18 61.36 31.75 15.88 593 103 4:38 1.658
2 femaleleft 172.72 65.90 33.02 16.51 389 215 4:30 1.717
3 male left 187.96 75.00 45.72 22.86 430 260 5;13 2.024
4 female left 170.18 59.09 20.32 10.16 472 72 3:44 1.543
5 male left 177.80 59.09 50.80 25.40 453 319 4:00 1.466
6 male left 182.42 91.81 50.80 25.40 824 438 4:20 2.398
7 male left 182.88 74.09 43.18 21.59 640 434 3:53 1.939
8 female left 167.64 73.63 25.40 12.70 606 243 4:36 1.943
9 male left 172.72 79.54 35.56 17.78 807 294 4:00 2.000
10 female left 177.80 75.00 30.48 15.24 724 208 4:45 2.099
11 male left 167.64 54.54 53.34 26.67 617 110 3:30 1.317
12 female left 177.80 72.72 21.59 10.80 497 222 4:31 1.895
13 male left 182.88 70.45 43.18 21.59 496 231 5:03 1.854
14 female left 170.18 63.63 29.21 14.61 975 135 5:00 1.766
15 female left 147.32 45.45 34.29 17.15 360 58 3:42 1.325
16 male left 190.50 88.63 46.99 23.50 442 140 4;30 2.29
17 female left 157.48 50.90 36.83 18.42 335 85 3:00 1.469
18 female left 185.42 70.45 25.40 12.70 419 92 4:04 1.798
19 female left 165.10 47.72 19.05 9.53 318 56 6:11 1.398
20 female left 170.18 63.63 27.94 13.97 412 64 4:45 1.717
Mean 173.840 67.132 35.243 17.621540.450 188.950 0.181 1.781
STD 10.452 12.462 10.720 5.360 179.668 118.130 0.030 0.305












Isokinetic Protocol Data


Table E-2. Pretest Isokinetic Data.
Subject Ave-Vert- AveMed/Lat- AveAnt/Pos- Ave- Ave- Ave-Ankle Ave-KneeF Ave-KneeV
SubjectTS TTS TTS GRF-F1 GRF-F2 Ave-Ankle Ave-KneeF Ave-KneeV
TTS TTS TTS GRF-F1 GRF-F2
1 385.633 205.041 12.780 1196.825 2420.575 53.420 117.779 -0.005
2 305.617 815.163 10.558 1086.6542242.27673.726 137.275 0.020
3 284.501 31.117 443.978 1353.1523534.04262.067 128.099 0.051
4 304.505 78.905 204.485 2264.69278.130 134.345 -0.009
5 255.051 1535.107 599.564 1309.5693229.17071.431 120.652 0.068
6 361.739 397.857 752.373 1459.0593670.96573.708 114.982 0.016
7 283.390 1364.162 74.459 1327.7492334.91970.296 119.922 0.023
8 276.722 1526.416 25.561 1053.9792346.15291.401 137.436 0.050
9 238.381 643.462 210.597 1505.630 3364.18478.698 138.865 0.002
10 267.831 2008.735 370.074 1082.5122643.38866.220 136.940 -0.009
11 312.285 1211.909 640.683 1060.8612398.78463.890 119.608 0.090
12 312.285 87.795 472.872 824.468 2609.91966.129 136.575 0.033
13 351.737 21.671 1775.355 1215.124 2858.848 58.991 120.478 0.012
14 265.053 877.953 10.558 1269.7712026.38481.686 131.165 0.066
15 252.828 436.198 7.779 998.953 1759.75470.040 135.908 0.044
16 335.623 1208.019 470.761 1355.9993059.61961.809 120.026 0.037
17 262.275 11.113 1353.604 1181.8912327.59962.474 120.453 0.040
18 241.159 36.674 28.339 517.830 2675.81089.628 141.883 0.033
19 248.383 686.804 17.781 829.357 1308.20677.920 135.318 0.024
20 263.386 347.292 964.082 1209.2512379.74486.646 145.936 0.049












Table E-3. Posttest Isokinetic Data.
SubjectAve-Verrt- AveMed/Lat- AveAnt/Pos- Ave- Ave- Ave-Ankle Ave-KneeF Ave-KneeV
SubjectTS TTS TTS GRF-F1 GRF-F2 Ave-Ankle Ave-KneeF Ave-KneeV
TTS TTS TTS GRF-F1 GRF-F2
1 272.832 99.464 606.788 963.901 2187.47657.280 119.306 -0.008
2 322.287 371.182 7.224 1104.253 2419.85468.562 131.715 -0.007
3 262.830 17.781 7.224 1352.413 3748.178 70.768 129.609 0.037
4 380.076 1503.634 741.815 2591.46173.817 130.210 -0.004
5 352.570 442.311 6.112 1217.455 3682.61567.285 118.652 0.043
6 368.407 55.011 1385.833 1500.2963712.12976.943 114.005 0.018
7 277.278 792.381 766.264 1210.546 2464.040 75.098 125.190 0.019
8 287.835 58.901 29.450 1107.363 2475.97990.148 133.226 0.047
9 233.380 1047.432 1196.906 1307.4713292.264 80.540 138.799 0.008
10 253.384 266.720 54.455 1125.0722773.72666.095 138.202 -0.002
11 263.386 20.004 26.672 1138.3292864.93064.069 118.787 0.072
12 261.163 1137.450 1007.424 962.746 3452.65167.414 132.692 0.043
13 295.615 13.883 656.798 1507.215 3592.22360.882 124.143 0.014
14 297.837 53.344 11.669 1216.453 2090.325 78.476 130.427 0.084
15 333.400 47.232 409.526 1037.8681885.09266.288 132.220 0.041
16 297.282 613.456 492.321 1145.5313040.01765.149 119.426 0.037
17 235.047 11.113 983.530 1208.829 2726.988 58.354 121.955 0.014
18 200.596 30.006 19.448 2587.51194.440 143.115 0.042
19 225.601 383.410 13.336 859.659 1500.34274.305 137.629 0.021
20 302.283 53.344 11.113 1248.5152581.46877.931 137.376 0.055











Functional Protocol Data


Table E-4. Pretest Functional Data.
AveVert- AveMed/Lat AveAnt/Pos Ave Ave
Subject TTS TTS TTS GRF-F1 GRF-F2 Ave-Ankle Ave-KneeF Ave-KneeV
1 309.506 1036.674 1046.876 1141.1162664.65561.981 129.317 0.056
2 322.287 135.583 190.038 1523.9352913.466 81.230 126.765 0.004
3 310.618 501.767 33.896 1034.4373592.01465.190 124.388 0.051
4 211.709 16.670 589.562 389.054 2348.94487.639 128.753 0.042
5 320.620 345.625 953.524 1268.8223275.86963.958 128.112 0.027
6 371.185 503.990 45.009 1318.6803737.40763.673 111.110 0.027
7 357.849 974.639 31.673 1379.0983279.76168.593 118.702 0.013
8 258.941 734.591 23.338 925.211 2094.03972.705 137.854 0.018
9 247.827 192.261 307.839 1432.6483455.75776.160 133.928 0.039
10 248.383 53.900 9.446 1037.2023286.09471.471 133.180 0.041
11 318.953 1536.418 772.377 1032.5562544.800 66.229 111.482 0.053
12 270.610 703.474 57.789 1096.3762571.18476.160 136.207 0.001
13 280.612 1180.792 419.528 1258.7542974.85275.663 123.255 0.012
14 225.601 78.349 1193.572 1313.0192176.46471.891 141.148 0.055
15 206.708 127.248 340.068 826.179 1893.39670.040 135.908 0.042
16 362.850 260.052 71.681 1768.4912847.23356.513 113.272 0.005
17 226.712 870.730 741.259 919.924 2639.913 60.717 121.356 0.020
18 240.604 36.674 28.339 501.276 2424.93761.293 129.721 0.024
19 209.486 66.124 14.447 807.485 1465.02774.818 141.765 0.006
20 259.496 1110.222 6.112 1099.1602430.462 59.412 139.816 0.026













Table E-5. Posttest Functional Data.
AveMed/Lat- AveAnt/Pos- Ave Ave
Subject AveVert-TTS TTS TTS GRF-F1 GRF-F2 Ave-Ankle Ave-KneeF Ave-KneeV
1 292.281 35.563 48.343 1013.7382387.15156.848 125.968 0.031
2 293.948 21.671 11.113 1339.6263317.05577.957 124.459 0.013
3 253.940 57.234 17.226 980.144 3533.22664.820 130.208 0.045
4 247.272 485.653 740.704 1715.8992650.02290.775 138.095 0.039
5 342.291 25.005 632.904 930.004 3603.54064.661 129.306 0.042
6 335.067 667.911 45.009 1450.396 3462.41865.796 114.135 0.023
7 489.542 402.858 139.472 1188.2962930.46164.842 119.399 0.025
8 258.385 1308.039 47.787 512.813 2294.88281.106 142.812 0.037
9 261.163 245.049 921.851 1574.336 3572.76079.419 131.345 0.012
10 281.723 1124.669 176.702 928.309 3098.84573.942 131.713 0.027
11 1175.591 804.050 583.450 900.689 2840.39864.420 115.111 0.054
12 245.049 18.893 24.449 1198.3302068.20974.819 132.742 0.049
13 228.379 38.341 804.328 1138.250 2879.32178.875 120.075 0.016
14 232.269 393.412 475.095 1184.164 2199.688 70.651 136.546 0.047
15 230.602 25.005 100.576 1006.9312017.75466.288 132.220 0.039
16 373.408 1561.979 35.563 1622.3313135.60259.549 122.086 -0.002
17 1149.474 821.275 8.335 1002.2192474.58160.538 121.455 0.016
18 220.600 273.388 20.560 928.113 2585.36663.331 128.793 0.026
19 296.726 251.161 242.271 1074.8522032.64272.195 136.293 -0.001
20 252.273 2112.089 19.448 1054.508 2149.783 55.760 128.013 0.053















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BIOGRAPHICAL SKETCH

I was born in Jacksonville, FL, on October 16, 1978, to Mr. Raymond M.

Wikstrom and Mrs. Geraldine A. Wikstrom. My younger sister and I grew up as Navy

brats, moving around the country. Living in Jacksonville, FL, San Diego, CA, and

Alexandria, VA, exposed me to very different and unique views of life. I attended two

different high schools: Saint Augustine High School in San Diego and Bishop Ireton

High School in Alexandria. While in school, I lettered in two varsity sports, basketball

and tennis, and was a member of the National Honor Society. I graduated from high

school in 1997 and decided to attend Roanoke College in Salem, VA.

I came to Roanoke to major in athletic training, because of the inspiration givin to

me by the program director, Mr. Jim Buriak. While a demanding and time consuming

major, I never doubted my decision to become an athletic trainer or my decision to attend

Roanoke College. My time there was the best four years of my life. I graduated from

Roanoke College in 2001 and was accepted to continue my education at the University of

Florida.

As a first year graduate athletic trainer, I was sent to be the head athletic trainer at

Trenton High School. Despite the sense of overwhelming pressure of being a head

athletic trainer for the first time, I felt prepared and grateful for the mentoring of Mr. Jim

Buriak and Roanoke College. As a second year graduate assistant, I was assigned to be

the head athletic trainer at Eastside High School. Eastside has given me the opportunity

to grow as a clinician, teacher, and mentor and feels like a second home. I will be sad to






78


leave at the end of this year but excited to begin a new chapter in my life, as I begin work

towards my doctoral degree here at the University of Florida.