Citation
Torque Steadiness of the Ankle Plantar Flexors during a Concentric and Eccentric Isokinetic Movement

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Title:
Torque Steadiness of the Ankle Plantar Flexors during a Concentric and Eccentric Isokinetic Movement
Creator:
ROZEA, GERARD D. ( Author, Primary )
Copyright Date:
2008

Subjects

Subjects / Keywords:
Ankle ( jstor )
Electromyography ( jstor )
Flexors ( jstor )
Muscle spindles ( jstor )
Muscles ( jstor )
Range of motion ( jstor )
Sprains and strains ( jstor )
Tendons ( jstor )
Torque ( jstor )
Velocity ( jstor )

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University of Florida
Holding Location:
University of Florida
Rights Management:
Copyright Gerard D. Rozea. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Embargo Date:
5/31/2015
Resource Identifier:
670352235 ( OCLC )

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TORQUE STEADINESS OF THE ANKLE PLANTAR FLEXORS DURING A CONCENTRIC AND ECCENTRIC ISOKINETIC MOVEMENT By GERARD D. ROZEA A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2005

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Copyright 2005 by Gerard D. Rozea

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iii ACKNOWLEDGMENTS Many people have earned my gratitude for their guidance and support during my doctoral education and as I completed my disse rtation. First, I w ould like to thank my best friend and my wife, Chri stina, for her love, patience, and support through this long and difficult journey over the past few years. I would also like to thank my parents, Gerard and Mary Rozea, for their continue d encouragement during the pursuit of my doctorate and more importantly for providing me with the fundamental values to achieve my goals. I would like to express appreciation and thanks to Dr. Mark Tillman of the Department of Applied Physiology and Kine siology for his extensive time, patience, interest, and expertise in th is study and its findings. Without his assistance, the completion of my dissertation would not have be en possible. In addi tion, gratitude is also extended to Dr. Steven Dodd, Dr. Terese Chmi elewski, and Dr. Ronald Siders for their support, input and for serving as dissertation committee members. Special thanks are due to Theresa Stoeckel for her tireless assistance with data reduction and to the subjects who gave of their time, and were an invaluable help.

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iv TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iii LIST OF TABLES.............................................................................................................vi LIST OF FIGURES..........................................................................................................vii ABSTRACT.....................................................................................................................vi ii CHAPTER 1 INTRODUCTION........................................................................................................1 Statement of the Problem..............................................................................................3 Specific Aims................................................................................................................4 Experiments 1 and 2..............................................................................................4 Experiment 1.........................................................................................................4 Experiment 2.........................................................................................................4 Significance..................................................................................................................5 2 REVIEW OF LITERATURE.......................................................................................8 Anatomy of Skeletal Muscle........................................................................................8 Motor Unit, Muscle Spindles, and Golgi Tendon Organs..........................................10 Muscle Injury..............................................................................................................12 Muscle Actions...........................................................................................................13 Force-Velocity Relationship.......................................................................................14 Neural Control of CON and ECC Muscle Actions.....................................................15 Motor Unit Synchronization.......................................................................................17 Passive Component of Muscle and Torque Steadiness..............................................19 Stretching Effect on Neural Control of Muscle..........................................................21 Training Effect Including Maxi mal vs. Submaximal Training..................................23 Torque Steadiness.......................................................................................................25 Conclusion..................................................................................................................26 3 METHODS.................................................................................................................27 Participants.................................................................................................................27 Instrumentation...........................................................................................................28

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v Procedures...................................................................................................................29 Demographics......................................................................................................30 Electromyography...............................................................................................30 Kin-Com..............................................................................................................31 Experiment 1.......................................................................................................32 Torque Steadiness Testing...................................................................................32 Experiment 2.......................................................................................................34 Data Reduction...........................................................................................................35 Statistical Analyses.....................................................................................................36 4 RESULTS AND DISCUSSION.................................................................................38 Experiment 1 Results..................................................................................................38 Torque..................................................................................................................38 Electromyography...............................................................................................41 Experiment 2 Results..................................................................................................45 Torque..................................................................................................................45 Electromyography...............................................................................................47 5 DISCUSSION AND CONCLUSIONS......................................................................52 Experiments 1 and 2............................................................................................52 Experiment 1.......................................................................................................54 Experiment 1 Conclusions...................................................................................58 Experiment 2.......................................................................................................58 Experiment 2 Conclusions..................................................................................63 Future Research..........................................................................................................63 APPENDIX A UNIVERSITY OF FLORIDA INSTITUTIONAL REVIEW BOARD INFORMED CONSENT............................................................................................64 B LOCK HAVEN UNIVERSITY INSTITUTIONAL REVIEW BOARD INFORMED CONSENT............................................................................................73 C DATA COLLECTION FORM...................................................................................75 D LIST OF ABBREVIATIONS.....................................................................................76 LIST OF REFERENCES...................................................................................................78 BIOGRAPHICAL SKETCH.............................................................................................84

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vi LIST OF TABLES Table page 3-1 Characteristic test participants.................................................................................29 4-1 Mean coefficient of variation a nd absolute error for each treatment.......................39 4-2 Mean coefficient of variation a nd absolute error for each velocity.........................40 4-3 Mean coefficient of variation and absolute error for each muscle action................41 4-4 Lateral gastrocnemius and soleus mean EMG and peak/mean EMG ratios for each treatment..........................................................................................................43 4-5 Lateral gastrocnemius and soleus mean EMG and peak/mean EMG ratios for each velocity.............................................................................................................44 4-6 Lateral gastrocnemius and soleus means and peak/mean ratios for each muscle action........................................................................................................................4 5 4-7 Mean coefficient of variation a nd absolute error for each condition.......................47 4-8 Mean coefficient of variation a nd absolute error for each velocity.........................48 4-9 Mean coefficient of variation and absolute error for each muscle action................49 4-10 Lateral gastrocnemius and soleus mean EMG and peak/mean EMG ratios for each condition..........................................................................................................50 4-11 Lateral gastrocnemius and soleus mean EMG and peak/mean EMG ratios for each velocity.............................................................................................................51 4-12 Lateral gastrocnemius and soleus mean EMG and peak/mean EMG ratios for each muscle action...................................................................................................51

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vii LIST OF FIGURES Figure page 1-1 Flow chart of the study...............................................................................................7 2-1 Hill Model of Muscle.................................................................................................9 2-2 Skeletal Muscle Organi zation and Connective Tissue.............................................10 3-1 Electrode Placement over the soleus and lateral gastrocnemius..............................30 3-2 Participant in position (knee angle=60 ) for plantarflexor testing...........................31 3-3 Torque Readout from Kin-Com where th e top of the blue line was the target torque and the white line represente d the torque tracing produced by the participant.................................................................................................................32 5-1 Length tension rela tionship of muscle.....................................................................61

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viii Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy TORQUE STEADINESS OF THE ANKLE PLANTAR FLEXORS DURING A CONCENTRIC AND ECCENTRIC ISOKINETIC MOVEMENT By Gerard D. Rozea May 2005 Chair: Steven L. Dodd Cochair: Mark D. Tillman Major Department: Applied Physiology and Kinesiology Eccentric (ECC) muscle actions are a cruc ial part of movements that occur during everyday activities and during athletic competitions. Maximal ECC actions are up to 40% more forceful than maximal concentric (CON) actions and result in the greatest number of muscle injuries. In addition, ECC and CON seem to be controlled by different neural mechanisms. Consistent control of jo int motions (torque stead iness) via muscular actions may be useful in preventing injuries. For both experiments in this study, increasi ng velocity decreased torque steadiness, increased mean EMG activity, and decrea sed peak:mean (P/M) EMG activity. In Experiment 1, 15 treatment participants we re assessed before and after 1-week of submaximal CON and ECC training. Overa ll training improved pa rticipantsÂ’ torque steadiness, mean EMG activity, and decrea sed the P/M EMG activity. During the ECC action, torque steadiness and mean EMG ac tivity were less than CON, but P/M EMG

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ix activity was greater than CON. Since the trai ning protocol did improve the overall torque steadiness and muscle activity, it appears that submaximal CON/ECC training may be beneficial in preventing and tr eating muscle strain injuries. In Experiment 2, 15 participants perfor med the torque steadiness testing after stretching and after decreasing the dorsiflexion range of moti on. The absolute error score after stretching increased without a change in EMG activity. The CON and ECC did not differ significantly for torque steadiness. Mean EMG activity was less for ECC than for CON; and P/M EMG activity was greater duri ng the ECC. The combined effect of decreasing the muscle stiffness and the depres sed neural feedback may have affected the absolute error scores in the stretching c ondition. However, decr easing the dorsiflexion range of motion and therefore decreasing the pa ssive tension or stiffness of the muscle alone did not affect performance. Therefore, stretching appears to have an influence on motor control and may affect muscle pe rformance during athl etic activities.

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1 CHAPTER 1 INTRODUCTION Eccentric muscle actions are a crucial part of movements that occur during everyday activities as well as athletic co mpetitions. Eccentric (ECC) muscle actions occur when a muscle is active while it is leng thening. In this condition, the external force is greater than the muscle action resulting in muscle lengthening. A concentric (CON) action is defined as muscle shortening while the muscle is active, allowing it to overcome an external force. There are many differ ences between CON and ECC: the amount of force produced by the muscle, velocity depe ndence, and neural control mechanisms. Eccentric muscle actions are more forceful and are typically used for deceleration. Maximal ECC actions may be 40% more for ceful than maximal CON actions and result in the greatest number of muscle injuries. (Bishop, Trimble, Bauer & Kaminski, 2000; Komi & Burskirk, 1972; Doss & Karpovich, 1965) . Consistent control of joint motions (torque steadiness) via musc ular actions may be useful in preventing injuries. Differences between CON and ECC are not limited to force production. Concentric actions are velocity-dependent: maximal force exerted decreases as movement speed increases (Westing and Seger, 1989). Howeve r, eccentric muscle actions are affected only slightly by the speed of contraction (Enoka, 1996). In fact, ECC increases in force as the speed of movement initially increases from rest. Finally, CON and ECC seem to be controlled by different neural mechanis ms (Enoka, 1996). The differences between neural control of CON and E CC are apparent when investig ating the electromyelographic (EMG) activity during the two muscle acti ons. The level of EMG activity during

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2 maximal ECC is less than maximal CON indicat ing that the amount of voluntary neural activation by the nervous system is lower even though the amount of force generated is greater (Enoka, 1996; Westing, Seger and Thorstensson, 1990; Westing et al., 1989; Wickiewicz, Roy, Powell, Perrine, & Edgert on, 1984). The decreased EMG activity may represent a decrease in th e neural drive during maximal ECC (Enoka, 1996). This inhibition of neural drive to the muscle is thought to be a protective mechanism resulting in fewer muscle fibers being active and damaged. In addition to a decrease in neural drive, there appears to be an increase in the peripheral afferent feedback from the muscle spindles within the muscle during the ECC (Bishop et al., 2000; Burke, Hagbarth & Lofste dt, 1978). The increased afferent muscle spindle activity results in an increase in p eak EMG (spikes within the EMG) relative to the mean EMG activity during ECC (Bishop et al., 2000). These increased peaks during the ECC are caused by the synchronization of motor units during the ECC action (Yao, Fuglevand, & Enoka, 2000). Increased synchron ization of motor units decreases torque steadiness in isometric muscle actions. Ther efore, due to the increased muscle spindle afferent activity causing greater motor unit sy nchronization, it is lik ely that eccentric muscle actions would be less steady and not as well controlled as concentric actions. In addition, as the velocity of the movement is in creased it is likely th e torque steadiness for ECC will decrease further with less time fo r adjustments to be made by higher brain centers to the neural input. Our study tested, different conditions to a ffect torque steadiness to gain a better understanding of how muscle actions are ne urologically controlled. We used an

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3 intervention approach to affect neural feedb ack and control to help address these neural control issues. Statement of the Problem The purpose of this multiexperiment study was to determine the effects of muscle action (CON or ECC), cont raction velocity (10 /s, 20 /s, 30 /s, 40 /s), and certain conditions (training, decreasing the dorsif lexion range of motion, and stretching) on torque steadiness during CON and ECC (Figure 1-1). The specific experiments of the study were designed to answer the following questions: 1) How does training influence torque steadiness?, and 2) How does stretchi ng and decreasing the dorsiflexion range of motion influence torque steadines s? By investigating how an ECC action is activated, we may better understand the underlying neural c ontrol mechanisms that may be linked to muscle strains and to improve prev ention and rehabilitation techniques. In each experiment we conducted a baseline torque steadiness test to determine an individuals’ ability to maintain a constant torque during an isokinetic CON/ECC muscle action at 10, 20, and 30°/s. Ten participants from experiment 1and 11 participants from experiment 2 were also tested at 40 /s. Previous research shows that when muscle spindles are stretched more qui ckly, they send more afferent input that results in brief spikes of muscle activity (Trimble, Rozea, Frimel, 2001; Bishop et al. 2000) that could impair torque steadiness. In Experiment 1, after initial torque steadiness testing, we tested the effects of 1week of submaximal training on torque stead iness. Maximal training decreases torque steadiness (Bishop et al., 2000) but this may be due to an increase in synchronization associated with early neurological adaptations to training. Neural changes associated

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4 with training are greatest in the early phase. Longer duration training has fewer neurological effects (Sale, 1988). Experiment 2 was designed to determine th e effects on torque steadiness of altering the passive tension during the isokinetic C ON/ECC actions either stretching (PS), or decreasing the dorsiflexion range of motion (DRM ). Effects of PS or DRM were used in an attempt to reduce the muscle spindle f eedback and to affect torque steadiness. Specific Aims The specific aims for each phase of the proposed project follow: Experiments 1 and 2 1. To determine if increasing velocity will decrease torque steadiness. 2. To determine if increasing velocity would increase the mean EMG activity for the plantar flexors. 3. To determine if increasing velocity would decrease the ratio of peak to mean EMG activity for the plantar flexors. Experiment 1 1. To determine if submaximal training would increase torque steadiness. 2. To determine if submaximal training w ould increase mean EMG activity of the plantar flexor muscles. 3. To determine if submaximal training woul d decrease the ratio of peak to mean EMG activity of the plantar flexor muscles. 4. To determine if submaximal training w ould improve the torq ue steadiness during the ECC. 5. To determine if submaximal training would decrease the ratio of the peak to mean EMG activity of the plantar flexor muscles during the ECC. 6. To determine if submaximal training would increase the mean EMG activity of the plantar flexor muscles during the ECC. Experiment 2 1. To determine if the passive stretching pr otocol increased ankl e dorsiflexion range of motion.

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5 2. To determine if decreasing the dorsiflex ion range of motion or stretching would decrease torque steadiness. 3. To determine if decreasing the dorsiflex ion range of motion or stretching would affect the mean EMG activity or the rati o of peak to mean EMG activity of the ankle plantar flexors. 4. To determine if decreasing the dorsiflex ion range of motion or stretching would improve torque steadiness during ECC. 5. To determine if decreasing the dorsiflex ion range of motion or stretching would affect the mean EMG activity of th e ankle plantar flexors during ECC. 6. To determine if decreasing the dorsiflex ion range of motion or stretching would affect the ratio of the peak to mean EMG activity of the ankle plantar flexors during ECC. Significance Current understanding of neural control of eccentric muscle actions is limited. Enoka (1996) described eccentric actions as re quiring unique activation strategies by the nervous system. Presently, it is unclear what these neural strategies are or how they receive input to control such actions. Bishop et al. (2000) de scribed an increase in motorunit synchronization with ECC actions compared to CON. They attributed this increase in motor-unit synchronization to an increase in muscle spindle afferent activity. They also found increased motor-un it synchronization afte r a period of maximal ECC training, but gave no clear explanation. Yao et al. (2000) noted decreased torque steadiness with increased motor-unit synchronization. In the present investig ation, decreasing the dorsiflexion range of motion was an attempt to determine how decr easing the stretch on the muscle spindles affects their afferent f eedback and resulting torque steadiness. The stretching protocol examined th e role of muscle spindle affe rent activity. The influence of stretching on performance and injury pr evention remains unclear. Decreased muscle spindle afferent activity after stretching results in decrease d muscle strength and power

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6 and was hypothesized to decrease torque steadin ess. This inhibition of muscle spindles may affect athletic performance and create a potential for injury. Bishop et al. (2000) concluded that in a small subgroup (n = 3) of participants, a training program using maximal eccentric exer cises decreased torque steadiness: the reason for is unclear. In the present study, pa rticipants were trai ned at 40% of their maximum plantar flexor torque. The training was designed to be more specific to the task they performed during the torque steadine ss testing. This type of training may help prevent and treat athletic injuries. Improving our knowledge regarding the sync hronization of motor units and its effect on torque steadiness and control during eccentric actio ns can enhance our understanding of eccentric muscle actions and may lead to improved rehabilitation techniques. This information can also provide insight into injury preventi on strategies.

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7 Figure 1-1. Flow chart of the study Experiment 2 Condition influence on Torque Steadiness n = 1 5 Experiment 1 Training influence on Torque Steadiness n = 30 Dependent Variables Torque (CV and Absolute error) Mean EMG activity gastrocnemius Mean EMG activity soleus Peak/Mean EMG activity gastrocnemius Peak/Mean EMG activity soleus Independent Variables Velocity Muscle action Condition (B, DRM, PS) Independent Variables Velocity Muscle action Treatment (BT, BC, PTC, and PT) Control Group n = 15 Experimental Group n = 15

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8 CHAPTER 2 REVIEW OF LITERATURE Physical activity can result in many types of injuries including sprains, strains, and fractures. The prevention, treatment, and mech anism of muscle stra in injuries are the least understood (Brockett, Morgan, & Proske, 2004). Many predisposing factors contribute to the mechanism of muscle st rains including fatigue, poor flexibility, poor muscle strength, and improper agonist:antagoni st. However there is little agreement about the true cause of muscle strains. The cause of muscle strains has been described as a complex neuromuscular coordination pattern th at to date is unclear (Best & Garrett, 1996). Therefore, we reviewed the relevant information on neurological control of muscle actions. Anatomy of Skeletal Muscle Skeletal muscle is the only tissue in th e body that is capable of contracting or creating tension and shortening in length. In addition, muscle has the properties of extensibility that allows it to increase in length, and elasticity, which lets the muscle return to its original length after stretching (Hall, 2002). Muscle has active and passive components allowing for these viscoelastic properties. The active component includes the contractile part of the muscle. This ac tive component allows the muscle to develop tension through the stimulation of muscle fibers. The passive component is composed of both a parallel elastic component (PEC) and a series elastic compone nt (SEC) that helps transmit forces from within the muscle to th e skeleton (Figure 2-1). The PEC is made of proteins that provide connections within the muscle allowing the forces from the muscle

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9 to be transmitted longitudinally and laterally. These proteins include titan, intermediate filaments, and focal adhesions. The SEC is made of tendons and provides the attachment of the muscle to the skeleton and can add elastic energy dur ing dynamic movement. Skeletal muscle is held together by connec tive tissue (Figure 2-2) (Van De Graaff, 2002). Each muscle fiber (m uscle cell) is surrounded by connective tissue called the endomysium. Groups of muscle fibers, called fa scicles, are in turn held together by the perimysium. Finally, the whole skeletal musc le, composed of many fasciculi, is held together by the epimysium. Through this arrangement of conn ective tissue (PEC), contractions from each fiber can be transmitted throughout the muscle causing the entire muscle to contract as a unit. Figure 2-1. Hill Model of Musc le (adapted from Hall, 2003) Muscle and the tendon connect at the mu sculotendinous junction (MTJ). “The myofibrils and connective tissue (collagen) are attached in se veral layers of folds (Enoka, 2002b p. 227).” This arrangement tissue makes the connection very strong and resistant to tears. Typically injuries occur in the skeletal muscle near the MTJ and not in the actual connections at the MTJ (Garrett, 1996).

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10 Motor Unit, Muscle Spindles, and Golgi Tendon Organs Muscle fibers are innervated by nerves that cause them to contract. A motor unit is a single motor neuron and all of the muscle fibers that it innerv ates (Saladin, 2004; Enoka, 2002). When stimulated to contract, all of the muscle fibers that are innervated by the nerve contract completely. The ratio of motor units to muscle fibers is dependent on the function of the muscle, the more precis e the movements, the lower the ratio. The opposite is true for gross movements. When greater muscle contraction forces are needed, more motor units are recruited. Figure 2-2. Skeletal Muscle Organization and Connective Tiss ue (adapted from Van De Graaff, 2002) Muscles are also infused with receptors (proprioceptors) that provide afferent feedback to the central nervous system (C NS) (Saladin, 2004; Enoka, 2002). In muscle there are two primary types of proprioceptors , muscle spindles and Golgi tendon organs, that provide feedback about body position and movements (Houk, Singer, & Henneman, 1971). Muscle spindles are found throughout th e gastor of the muscle and are more abundant in muscles that require fine cont rol (Houk & Henneman, 1967a). Muscle fibers

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11 are classified as extrafusal throughout the mu scle, intrafusal muscle fibers are found in the muscle spindle. Extrafusal muscle can contract throughout the en tire muscle, whereas the intrafusal muscle fibers are only capable of contraction at the ends. Contraction of the intrafusal fibers helps to stretch the centr al region of the muscle spindle and therefore sends afferent feedback to the CNS. This is particularly important during concentric contractions so the muscle can provide f eedback even during shortening. Muscle spindles have afferent and e fferent nerve fibers that send information to and from the CNS respectively. The primary afferent (Ia) fibers of the muscle spindle are coiled around the central region of the intrafusal fibers and provide feedback typically at the onset of stretch. The secondary afferent (I I) fibers respond mostly to prolonged muscle stretch and are located at the ends of the intr afusal fibers. The effe rent nerve fibers are composed of both gamma ( ) and alpha ( ) motor neurons. The motor neurons cause contraction of the intr afusal fibers and the motor neurons cause whole muscle actions. This feedback is critical to movements because the Ia neurons send information to the CNS about the movement and the motor neuron sends information to make adjustments. Golgi tendon organs are located in the tendon near the musculotendinous junction (Houk & Henneman, 1967b). When a muscle is contracted or passively stretched, the Golgi tendon organs are compressed within the collagen fibers and provide feedback about the degree of muscle tension. When there is excessive tension on the tendon, the Golgi tendon organs send inhibitory informati on to the CNS to reduce the strength of the muscle contraction in order to try to prot ect the muscle from injury (Houk & Henneman 1967b).

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12 Muscle Injury Muscle injuries are the most common injuries in athletic competition accounting for 10 to 55% of all injuries (Jarvinen, Kaariainen, & Jarv inen, 2000). Over 90% of the muscle injuries occur from a contusion or dynamic overload of the muscle from excessive strain. Muscle strains occur most fr equently in sprint type athletes in sports such as football and track-and-field (Brocke tt et al., 2004; Jarvinen et al., 2000). These injuries often occur to the hamstring musc les, primarily the biceps femoris, during demanding eccentric muscle actions (Brockett et al., 2004; Jarvinen et al., 2000; Garrett, 1996). As previously mentioned, these injuries typically occur in the muscle fibers near the musculotendinous junction. In addition, mu scles that function about two joints, such as the rectus femoris, gastrocnemius, and semitendinosis, have the greatest frequency of injury since they can be elongated across two jo ints (Jarvinen et al., 2000; Garrett, 1996). It has been reported that up to 16% of the tim e missed in the Australi an Football League (AFL) is the result of muscle strains, particul arly to the hamstrings (Brockett et al., 2004). In addition, even after an indivi dual returns to activity, muscle strains frequently continue to be a source of pain and impairment of performance (Safran, Ga rrett, Seaber, Glisson, & Ribbeck, 1988) Many predisposing factors may cause muscle strain injuries including fatigue, poor flexibility, and a low hamstring-to-quadriceps st rength ratio. Currently, there is a lack of agreement regarding the influence of these factors and muscle injury (Brokett et al. 2004). Some evidence indicates that muscle st rength after injury is normal compared to uninjured individuals indicating the lack of muscle strength was not the contributing factor in the muscle injury (Brokett et al. 2004). In addi tion, Thacker et al. (2004) found that stretching was not signifi cantly associated with a reduc tion in the total number of

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13 heel/calf or hamstring muscle injuries. Since little eviden ce supports thes e predisposing factors individually, muscle injuries are the result of a combinati on of factors and are probably related to a complex neural contro l mechanism (Brokett et al., 2004). However, to date our knowledge of the neural control of ECC is lim ited. A better understanding neural control, especially of ECC, may be helpful in th e prevention and treatment of muscle injuries. Muscle Actions A contraction is the result of the muscle’s ability to create tension and shorten in length (Saladin, 2004). When a muscle is stim ulated to contract by a nerve, it does not always result in muscle shortening; therefor e it might be more a ppropriate to describe “contractions” simply as muscle actions (Enoka, 1996; Kreighbaum & Barthels, 1996). Three distinctly different muscle actions can occur when a muscle is stimulated. First when muscle shortens and overcomes an extern al resistance resulting in a decrease in joint angle, a concentric (CON) muscle acti on has occurred. An eccentric (ECC) muscle action occurs when the muscle lengthens while it is active; theref ore the resistance is greater than the torque resulti ng from the muscle force, which causes an increase in the joint angle. Finally, stationary muscle acti ons or isometric (ISOM) muscle actions occur when the joint angle does not change and the to rque created by the muscle is equal to the external resistance (Enoka, 1996; Kreighbaum et al., 1996). Each of these types of muscle actions serves a different function. C oncentric muscle actions are most useful in creating movement of body parts. Eccentric muscle actions are used in resisting or controlling the action of a body pa rt. Finally, isometric musc le actions are useful in stabilizing a body part (particu larly joints). There are many differences among muscle

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14 actions including variations in CON and E CC velocity dependence and neural control mechanisms. Force-Velocity Relationship As stated previously, there are many differences between ECC and CON, one difference can be revealed in the force-ve locity relationship. The amount of force the muscle can exert is dependent on the velocity of the movement and the type of muscle action, either CON or ECC (Enoka, 1996; Westing et al., 1989; Bigland, & Lippold, 1954). During CON, the amount of force that can be exerted decrea ses as the velocity increases. However, ECC is almost unaffect ed by the velocity of movement except for a slight increase in force fro m ISOM (Arnold, Perrin, Kahler , Gansneder, & Gieck, 1997; Westing et al., 1989). This force-velocity relationship has been demonstrated in muscle preparations, but was found not to be exactly the same in vivo (Wickiewicz et al., 1984; Perrin et al., 1978). The amount of torque exerted in vi vo during lower velocity CON and during ECC was found to be less than was predicted in mu scle preparations. A llen et al. (1995) and Westing et al. (1990) superimposed electrica l stimulation during maximal muscle actions and found that the participants were able to a ttain greater forces than without electrical stimulation in ECC but not CON or ISOM. It has therefore been theorized the reason for lower in vivo maximal torque production must be the result of a tension-limiting neural regulatory mechanism that prevents excessive muscle loading by recruiting fewer muscle fibers and therefore minimizes the number of muscle fibers that may be damaged (Bishop et al., 2000). Westing et al. (1990) and Lundberg et al. (1978) theorized that this might be the result of an inhibitory feedback from Ib afferents that monitor muscle tension and

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15 provide negative feedback onto -motoneurons via an inhibitory pathway (Houk & Henneman, 1967a). Muscle torque production also vari es depending on the joint angle during isokinetic movements as described by the leng th tension curve where torque is greatest around the middle of the range of motion (ROM) and least at the onset and ends of the movements (Arnold et al., 1997). The diffe rences in muscle torque production throughout the ROM are the result of muscle architecture and leverage factors (Westing et al., 1989). Neural Control of CON and ECC Muscle Actions In addition to the velocity dependence differences, total force production and the neural control strategies re sponsible for the muscle activ ation vary between CON and ECC. In order to understand neural contro l of ECC, recall that ECC are capable of exerting greater forces compared to CON (Tesch, Dudley, Duvoisin, Hather, & Harris, 1990). Eccentric muscle actions result in grea ter muscle force, up to 40% greater than CON and 13.5% greater than isometric force (Doss et al., 1965). In addition, CON and ECC are controlled by different neural strategi es as is evident in the EMG activity during each muscle action (Tesch et al., 1990; Na rdone, & Schieppati, 1988). Compared to CON, ECC require lower levels of voluntary activation as de monstrated by lower levels of EMG activity. As a result, it is believed th at a maximal ECC is more likely to result in damage to the muscle than CON in part because of the greater forces on fewer numbers of motor units recruited as demonstrated by the lower levels of EMG activity during ECC (Enoka, 1996).

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16 CON, ECC, or ISOM muscle actions o ccur when the resistance applied is less than, greater than, or equal to the amount of muscle force exer ted (Enoka, 2000). In addition to muscle force exerted, the amount of muscle activation as measured by EMG activity is different for CON than ECC as demonstrated by the effect of velocity on neural control (Burke et al., 1978). As mentioned prev iously, although maximal ECC result in greater torque than CON, the amount of EMG activity is less during ECC and is relatively unaffected by speed. However, CON EMG activity is greater than ECC EMG activity and increases as the ve locity of the movement increas es (Tesch et al., 1990). As stated previously, this decreased ECC EMG activity may be the result of a protective neural mechanism that attempts to limit the amount of tension within the muscle (Abbruzzese, Morena, Spadavecchia, & Schieppa ti, 1994; Tesche et al., 1990; Burke et al., 1978). In experiments involving muscle act ivation during maximal voluntary muscle actions, participants were able to achieve near maximal activation when performing ISOM and CON (Allen et al., 1995; Westing et al., 1990). However, ECC torque appears to be almost 20% lower during voluntary activation than can be achieved with superimposed electrical stimulation during the muscle action. This decreased muscle activation during ECC appears to provide further evidence of a tension limiting mechanism of the nervous system that is uni que compared to either CON or ISOM. By activating fewer muscle fibers, this tension limiting mechanism appears to be protective in nature by activating fewer muscle fibers. As described previously, ECC exert great er forces compared to CON and require lower levels of voluntary ac tivation demonstrated by lowe r mean EMG activity (Bishop

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17 et al., 2000; Enoka, 1996). Eccentric muscle act ions demonstrate lower levels of mean EMG activity, but have greater peak EMG activ ity. Mean EMG activity is an indicator of the average level of activity within the muscle. Peak EMG activity of ECC is an indicator of the instantaneous level of muscle activation. Br ief increases in facilitation from spindle primary afferents via the segmen tal stretch reflex are a reflection of motor unit synchronization and cause greater peak s in the EMG activity (Bishop et al., 2000; Abbruzzes et al., 1994; Burke et al., 1978). Greater peak EMG activity associated with higher levels of spindle afferent activity and motor unit synchronization occurs to a greater extent during ECC. Bi shop et al. (2000) investigated the relationship of peak, mean and a ratio of peak to mean (P/M ) EMG activity of CON and ECC. They concluded that the mean EMG activity is gr eater for CON, whereas peak and peak to mean ratio of EMG activity was greater for ECC. The peak to mean EMG activity ratio was determined for maximal contractions but to date the ratio of P/M EMG activity has not been evaluated during submaximal contractions. Motor Unit Synchronization Motor units typically fire independent of one another during voluntary muscle actions (Milner-Brown, Stein, & Lee, 1975) . This phenomenon is called asynchrony. However, in some situations the timing of action potentials discharged by motor units is more correlated resulting in motor unit synchronization as a result of muscle spindle afferent input. Motor unit synchronization wa s initially studied in the hands of strength trained individuals where it was determined that motor unit synchronization was greater than in non-strength trained individuals (Miln er-Brown et al., 1975). However, in the hand muscles of skill-trained individuals like the hand muscles of musicians, motor unit synchronization is lower than that found in the hands of strength -trained individuals

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18 (Semmler, Kornatz, Dinenno, & Enoka, 2002; Miln er-Brown et al., 1975). Therefore, the fine motor coordination in the hand of skill-trai ned individuals is better than in strengthtrained individuals in part because of the greater synchronization of motor units in the hands of strength tr ained individuals. Yao et al. (2000) determined that motor-u nit synchrony increases the amplitude of fluctuations in force caused by the motor res ponse to the spikes or peaks in afferent feedback. As mentione d previously, motor unit synchronization is reflected by increased EMG activity causing greater peaks (Burke et al ., 1978). There are greater spikes in motor unit activation during ECC th an in CON (Bishop et al., 2000). These spikes are thought to be the result of higher levels of spindle affe rent feedback causing more synchronization of motor unit activation du ring the ECC. Further, eccentric muscle actions result in the activati on of high-threshold motor units compared to CON and cause greater motor unit synchronization (Howell, Fuglevand, Walsh, & Bigland-Ritchie, 1995). Therefore, ECC have lower average le vels of EMG amplitude but larger peak EMG amplitude than CON. Motor unit synchr onization occurs more frequently in ECC than CON as indicated by increased p eak EMG activity. The greater motor unit synchronization during ECC may be related to muscle injury by creating brief large spikes in muscle activation of few fibers. Motor unit synchronization causes these force fluctuation and would be reflected by a d ecrease in torque steadiness during ECC. Therefore, by investigating the effects of training on motor unit synchrony during ECC, it was hoped that this type of training would improve torque steadiness and would be an effective rehabilitative technique.

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19 Passive Component of Muscle and Torque Steadiness As a muscle contracts the active component increases cau sing an increase in the tension placed on the passive component (Enoka, 2000; Enoka, 1996; Wilson, Murphy, & Pryor, 1994). In addition, as a muscle is stre tched, either actively or passively, there is also an increase in the te nsion placed on the passive component. Within the muscle tendon are the golgi tendon organs (GTO) that are compressed as the tension in the SEC is increased (Enoka, 1996; Enoka, 2000). The GT O send a volley of afferent input to the spinal cord in response to the tension. In addition, as the muscle stretches, the muscle spindles (MS) are excited and send a volley of information to the spinal cord (Ogiso, McBride, Finni, & Komi, 2002). The resultant response of GTO is an inhibition of the muscle, while the MS causes an increased excitation of the muscle. This information is used, in addition to other receptors along with other afferent inputs from joint receptors and skin receptors, to modul ate and control the force produ ced. By modifying movement parameters so that individuals were exerci sing away from the end of joint ROM, the contribution of the passive tension from the series and parallel components of the triceps surae would be decreased during the ECC ac tivity. This decrease in passive tension would result in a decrease in GTO feedback to the spinal cord a bout the activity being performed and may result in a decr ease in torque steadiness. The stretch-shortening cycle (SSC) comb ines a quick ECC followed immediately by a CON (Enoka, 1996). The stretch-shorte ning cycle occurs in many activities including walking, running, and jumping and provides great benefits over CON only activities. A typical example of the st retch-shortening cycle is observable during jumping. When comparing the stretch-shor tening cycle versus a CON only maximum vertical jump, the stretch-shor tening cycle shows a greater muscle force at the beginning

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20 of the CON phase and a great er total work performed (B obbert, 2001; Bobbert, Huijing, & Jan van Ingen Schenau, 1986; Cavagna, Dusm an, & Margaria, 1968). The use of the SSC increases the efficiency of the muscle action and results in a significant increase in maximum jump height (Komi & Bosco, 1978). In addition to storing elas tic energy in the series el astic component, the stretchshortening cycle may also evoke the stretch reflex (Komi & Gollhoger, 1997). However, there may not be enough time for the sensory information to be transmitted from the receptors to the spinal cord during a rapi d SSC. During slower movements the reflex response may be more visible in the performan ce of the activity since there is more time to respond to sensory afferent feedback. Howe ver, the contribution of the stretch reflex to the control of these slower activities remains unclear. It was our hypothesis that the control of the ECC, as measured by torque steadiness in this investigation, would decrease with increasing velocity due to reduc ed time for feedback and corrections from the sensory input. As described previously, muscle is a vi scoelastic material that has elastic properties. The elastic component is found in the muscle (PEC) and tendon (SEC) and can have a significant affect on muscle pe rformance (Wilson et al., 1994). A highly compliant SEC increases the elastic energy st ored during the SSC movements. However, it has been demonstrated that a stiffer muscul otendinous unit is more beneficial to CON, ECC, and ISOM performances (Wilson et al., 1994) and results in greater force production. When a muscle acts either con centrically or isometrically, the muscle shortens causing tension to be exerted on the SEC, causing the SEC to lengthen. A stiffer SEC would result in quicker and greater forc e transmission by the contractile element of

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21 the muscle. Interestingly, in ECC, a stiffer SEC may be detrimental because the muscle would be lengthened further moving the actin and myosin further away from each other making the muscle action less effective (Wils on et al., 1994). Another consequence of this increased stiffness is a greater extent of muscle damage with ECC activity over individuals with more compliant ten dons (McHugh, Connolly, Eston, Kremenic, Nicholas, & Gleim, 1999). Stretching Effect on Neural Control of Muscle Static stretching has been used therapeu tically to improve flexibility, minimize muscle soreness, and to decr ease susceptibility to muscle injury (Garrett, 1996). The effects of static stretching ha ve been demonstrated to signi ficantly improve the range of motion (ROM) of the hamstring muscles and can last approximately 3 minutes after the stretching protocol (DePino, Webright, & Arnold, 2000). Th e principles behind passive stretching are based on the neurophysiological effects of the stretch reflex. When a muscle is initially stretched, the muscle spindl e detects the change in length and sends Ia afferent feedback to the CNS regarding the st retch. The initial res ponse results in muscle contraction against the stretc h. If the stretch position is held, the Golgi tendons respond to the increase in tension by sending Ib affere nt feedback to the central nervous system and cause the muscle to reflexively relax. Th is inhibition makes the Ia afferent feedback from the muscle spindles less likely to activate the muscle with subsequent stretches (Avela, Finni, Liikavainio, Niemela, & Komi, 2004). Stretching prior to activity is a common pr actice for injury prevention. However, the effectiveness of stretching for injury pr evention is debatable. More recently, it has been demonstrated that an acute bout of pa ssive muscle stretching prior to activity can have a negative effect on maximal for ce/power (Cornwell, Nelson, & Sidaway, 2002;

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22 Kokkonen, Nelson, & Cornwell, 1998). It is beli eved that there are two mechanisms that may cause this decrease in maximal performance. The first mechanism that is thought to contribute to the decrease in performance includes a decrease in muscle stiffness (Cornwell et al., 2002; Kokkonen et al., 1998). The source of the decrease in passive force has been postulated to be the molecular spring titin and was determined to be in the PEC (Herzog, Schachar, & Leonard, 2003). The second mechanism suggested to decrease muscle performance is a depression in muscle activa tion as a result of inhibition from the Golgi tendon organs (Guissard, & Duchateau, 2004; Kokkonen et al., 1998). Cornwell et al. (2002) tested the me chanisms thought to decrease muscle performance using two dynamic movements, a static jump and a c ountermovement jump. Their results were inconclusive in that they found a significant decr ease in jump height for the countermovement but not for the sta tic jump following stretching. They noted that there was a significant but small increase in muscle stiffness of the triceps surae, which they stated, would not be enough to aff ect performance. In addition, their results were inconclusive for depression of muscle activation. The post stretch static jump decreased EMG activity, but no change was noted for the countermovement jump following stretching. They concluded perfor mance was negatively affected, but it still remains unclear the contribution of the two m echanisms proposed. However, Guissard et al. (2004) used a 1-month static stretch traini ng protocol and showed that the increase in joint ROM was related to a decrease in muscle stiffness and a reduction in the stretch reflex. In addition, Guissard et al. (2004) found no effect on muscle torque with training. Therefore, the effects of stretching on mu scle performance and the mechanisms causing these changes remain unclear. Therefore, it was hypothesized that stretching prior to

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23 torque steadiness testing, as performed in this investigation, will result in a decrease in muscle stiffness and feedback from the MS reflected by a decrease in control. Training Effect Including M aximal vs. Submaximal Training The effects of training on muscle physiol ogy and neural control have been a source of great interest and debate. ECC training results in greater improvements in muscle strength compared to CON (Dudley, Te sch, Miller, & Buchanan, 1991; Colliander & Tesch, 1990; Komi et al., 1972). Improvement s in muscle strength are task dependent and are determined by the type of training th at is performed. Greater increases in ECC occur with ECC training and similar fo r CON (Enoka, 1996; Hortobagyi, Barrier, Braspennincx, Koens, Devita, Dempsey, & Lambert, 1996; Hortobagyi, Hill, Houmard, Fraser, Lambert, & Israel, 1996). Improvement s in muscle strength following resistance training have revealed muscle hypertrophy but the short-term improvements in muscle strength are attributed to neural adapta tions as measured by EMG activity (Higbie, Cureton, Warren, & Prior, 1996). The physiologi cal and neural changes associated with resistance training are disputable. Hortobagy i et al. (1996) revealed that submaximal ECC training resulted in a greater increase in muscle strength and EMG activity than CON. They attributed th e greater improvements in muscle strength during ECC over CON to greater muscle hypertrophy and ne ural adaptation with ECC. Whereas, Thorstensson, Karlsson, Viitasalo, Luhtanen, & Domi (1976) found increases in strength after 8 weeks of progressive strength training but no signi ficant changes in muscle activity as measured by EMG or hypertrophy. They attributed the improvements in muscle strength to an improvement in the e fficiency of the coordi nation of motor units. In contrast, Sale et al. (1988) reported that an increase in musc le strength is related to an increase in EMG activity. The increases in EMG activity with training are believed to

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24 indicate an increase in an individualÂ’s abilit y to more fully activate muscles in the early stages of training (Sale, 1988). Sale ( 1988) also reported that when hypertrophy of muscle fibers does occur following more prol onged training, the mo tor unit activation or the number of active motor units decreases. There seems to be some agreement that the neural effects of resistance training demonstrating increases in EMG activity were greatest in the early part of training but began to decline as training duration con tinued (Hortobagyi et al., 1996; Hakkinen, & Komi, 1983). The adaptations are attributed to greater neural efficiency with training. It has also been suggested that these early improvements in training are attributed to increased recruitment of synchronously contra cting motor units (Komi, & Buskirk, 1972) and that these results will typically last between one and three weeks. Enoka (1997), Sale (1988), and Milner-Brown et al. (1975) explai ned that increases in muscle strength are accompanied by an incr ease in motor unit synchronization. Bishop et al. (2000) trained a subgr oup of three participants using maximal ECC training and concluded that the peak torque increased and the torque steadiness decreased. Using maximal ECC training has been demonstrat ed to cause an increase in motor unit synchronization, which explains the decrea se in torque steadiness (Enoka, 2000). However, it is unclear how using submax imal torque steadiness training (as was performed in the current investigation) would affect motor unit synchronization and therefore torque steadiness. The use of resistance training to improve neural control has been demonstrated by measuring improvements in joint position sense in functionally unstable ankles (Docherty, Moore, & Arnold, 1998; Irrgang, Whitney, & Cox, 1994) and improvements

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25 in steadiness in individuals with essential tremor (Bilodeau, Keen, Sweeney, Shields, & Enoka, 2000). Docherty et al. ( 1998) felt the results were probab ly not attributed to joint receptors since they respond specifically to extreme ROM and local compression not full ROM movements. They theorized that thes e improvements related to muscle spindle efferent activity causing the muscle spindle to be more sensitive to stretch resulting in greater joint position sense. Irrgang et al. (1994) indi cated that af ter injury, improvements in proprioception could be obtained through the use of proprioceptive training. Since the resistance training in th ese studies improved joint position sense, the present study investigated the effects of trai ning on torque steadiness to contribute to the understanding of resistance training on motor control. Torque Steadiness Measuring torque steadiness during subm aximal ISOM, CON, and ECC has been used to quantify adaptations of the musculos keletal system in older adults (Tracy & Enoka, 2003). Recent research has investigat ed the difference between gender and age on torque steadiness during isometric musc le actions (Tracy, Byrnes, & Enoka, 2004; Tracy & Howard, 2004). They concluded that there are no differences in the magnitude of the fluctuations in motor output be tween gender and age as measured by the coefficient of variation. However, it has been demonstrated that pr e-clinically disabled older adults are less steady at higher intensity isotonic musc le actions and are less steady during CON than ECC (Manini, Baldwin, Van Arnam, & Ploutz-Snyder, 2004). It appears that the use of torque steadiness is an effective method of investigating neural control strategies and is not affected by age or gender. In an attempt to determine the effects of training on torque steadiness, Bishop et al. (2000) determined that even though the P/ M ratio decreased, torque steadiness as

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26 measured in their study had not improved. This may be the result of the technique they used for measuring torque st eadiness and/or the use of ma ximal training to investigate improvements in torque steadiness. Theref ore, it was hypothesized that with torque steadiness training in the curre nt study and the methods of measuring torque steadiness, ECC control will increase and motor unit synchronization will decrease. Conclusion Muscle strain injuries commonly occur in athletic competition and can result in a significant amount of time lost. It has been in dicated that muscle strain injuries occur during eccentric muscle actions. There is c onflicting literature on the effectiveness of traditional methods of stretching and strengthen ing to prevent these injuries. Recently much attention has been given to ECC because of the unique control strategies compared to CON. Eccentric muscle actions result in greater forces but less EMG activity than CON, but there are periods of brief spikes of high intensity activity of muscle fibers during ECC as a result of muscle spindl e afferent feedback called motor unit synchronization. It is believed that this high intens ity activity of fewer muscle fibers are related to increased risk of injury. The e ffect of submaximal training and stretching on improving the number of muscle fibers that are active and motor unit synchronization during ECC is unknown. Therefore, it appears th at a better understand ing of the level of muscle fiber activation and motor unit s ynchrony during ECC and the effect of submaximal training and stretching may be help ful in better understa nding muscle injury prevention and rehabilitation techniques.

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27 CHAPTER 3 METHODS The purpose of this study was to determ ine the effects of certain conditions, contraction speeds, and musc le action on torque steadine ss as measured by plantar flexion torque and mean and P/M EMG activity of the gastrocnemius and soleus muscles during an isokinetic action. In the first experiment each par ticipant completed 1-week of training and were tested on thei r ability to maintain a consta nt torque (torque steadiness) during the isokinetic CON/ ECC muscle action at 10 /s, 20 /s, 30 /s, and 40 /s initially and following 1-week of submaximal training at each speed. The second experiment was designed to determine the eff ects of altering the passive te nsion on the tor que steadiness during the CON/ECC actions by either decr easing the dorsiflexi on range of motion (DRM), or after stretching (PS). Participants A total of 45 healthy, college-aged male s and females from the University of Florida and Lock Haven University were recru ited for participation in this study. Fifteen participants were randomly assigned to each cond ition in each experiment of this study as determined by the a priori power analysis based on pilot data (Cohen, 1988). Before participating in either experi ment, each individual was inform ed of their rights as study participants as well as the st udy protocol. Additionally, the number of participants was consistent with research using similar methods and analyses including Tracy et al. (2004), Stevens et al. (2004), and Pinnige r et al. (2000) who all tested 11 participants. Thirty of the individuals recruited to participate in the current study were randomly entered into

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28 Experiment 1. Half of these participants (n = 15) were randomly assigned to complete the baseline (BT) measurement and then 1-week of training followed by a final measurement (PT). The other ha lf (n = 15) served as the co ntrol group and were tested at baseline (BC) and after 1-week without any training during that week (PC). The control group was matched to the treatment group on both age and gender individually. For Experiment 2, the remaining 15 participants completed three conditions assigned in a counterbalanced fashion: a) baseline (B), b) decreased dorsiflexion range of motion (DRM), and c) after stretch (PS). Each part icipant had a minimum of 15° of dorsiflexion and 15° of plantar flexion to be included in this study. This was necessary to allow the participant to complete the torque steadiness testing protocols. Any participant with a history of injury or surger y to their lower extremity pr ior to or during the study was excluded from this study because they may have undergone neural adaptation resulting from the injury that might affect this investig ation. Characteristics of the participants can be found in Table 3-1. Instrumentation Testing was completed in the Athletic Training/Sports Medicine Research Laboratory in the Florida Gym at the Universi ty of Florida and the Research Laboratory in Himes Science Laboratory Rehabilitation Center at Lock Have n University. A KinCom AP 125 (Chattanooga Group Inc., Chatta nooga, TN) was used to measure plantar flexor torque and ankle angle. The KinCom AP 125 was set up to test continuously through CON and ECC muscle actions. Torque data were collect ed at 100 Hz. A Myopac (Run Technologies, Laguna Hills, CA) EMG system was used to measure muscle activity. The Myopac was used to co llect the raw EMG signal at a sampling rate

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29 of 1000Hz (Pugh, 2003; Acierno, Baratta, & Solomonow, 2001). After sampling was complete, EMG data underwent an analog to digital (A/D) conversi on and was stored on a PC-type computer using the Data-Pac 2000 (Run Technologies, Laguna Hills, CA) analog data acquisition, processi ng, and analysis system. An electrogoniometer was used to measure ankle position at a sampling rate of 1000Hz. Electrogoniometer (Run Technologies, Laguna Hills, CA) data were us ed to synchronize the Kin-Com and EMG data. A BaselineTM goniometer (Fabrication Enterprise s Inc., Irvington, NY) was used to measure knee and ankle range of motion. Table 3-1. Characteristic test participants Experiment 1 Characteristic Treatment Control Exp 2 N 15 15 15 Age (yr) Mean 21.9 22.1 20.5 SD 2.8 3.5 2.7 Gender Male 6 6 3 Female 9 9 12 Mass (kg) Mean 74.4 75.5 67.6 SD 12.2 15.6 10.8 Height (cm) Mean 171.7 167.5 168.9 SD 12.0 7.9 6.1 PROM – DF Mean 22 20 20 (Deg) SD 6.3 5.0 6.1 PROM – PF Mean 62 60 60 (Deg) SD 6.4 4.6 5.6 Procedures Upon entering the lab, each participant was given a br ief overview of the study design and objectives. Any questions the participant had befo re volunteering to participate in the study were answered at th is time, if other questions arose during the

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30 project, they were addressed immediately. The participant then read and signed an informed consent form approved by the Institu tional Review Board of the University of Florida (Appendix A) and Lock Ha ven University (Appendix B). Demographics Following the initial explanation of the study objectives, demographic data were recorded including height, weight, age, gende r, and PROM for dorsiflexion and plantar flexion (Norkin & White, 2003) (Appendix C). Electromyography After the demographic information was obt ained, the participant was prepared for EMG analysis. Areas on the soleus and late ral gastrocnemius were shaved and the skin was cleaned with alcohol to decrease skin im pedance. Electrodes (BIOPAC, Goleta, CA) were placed 30 mm apart (center to center) ove r the muscle belly of the soleus and lateral gastrocnemius (Acierno et al., 2001)(Figure 3-1). Figure 3-1. Electrode Placement over the soleus and lateral gastrocnemius.

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31 Kin-Com After the EMG equipment was prepared, th e participant took a seat on the KinCom and was positioned according to manuf acturer instructions for right ankle plantar/dorsiflexion testing. Th e right ankle joint of the part icipant was aligned with the axis of the dynamometer. The right knee a ngle of the participant was measured (Norkin et al., 2003) to assure they were flex ed to 60° as measured by the Baseline goniometer (Figure 3-2). The participant was then strappe d in at the foot, ankle, knee, and thigh, to prevent accessory movements during the testing pr ocedure. A total of 25º of ankle range of motion was utilized (15° dorsiflexion, 10° plantar flexion) to allow for adequate passive and active muscle tension involvemen t. Testing was conducted in the CON/ECC mode. The gravity compensation option was used to account for limb weight. The screen display of their torque production was set up to show immediate and continual feedback to the participant during the testing procedure (Figure 3-3). Figure 3-2. Participant in position (knee angle=60 ) for plantarflexor testing.

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32 Figure 3-3. Torque Readout fr om Kin-Com where the top of the blue line was the target torque and the white line represente d the torque tracing produced by the participant. Experiment 1 Thirty participants were randomly assi gned to Experiment 1 to serve as the treatment (n = 15) or control (n = 15) gr oups. The control group was matched to the treatment group on both age and gender indivi dually. The control group was measured using the Torque Steadiness Te sting described below initia lly (BC) and after 1-week without any training during that week (PC). The treatment group was tested using the Torque Steadiness Testing described belo w initially (BT) and after 1-week of submaximal training (PT). Torque Steadiness Testing Once the participant was properly positioned, he/she was asked to perform three maximal voluntary isometric contractions (MVIC). To perform the MVICs the participant was asked to pus h down on a nonmoving footplate as hard as possible for 5 seconds. During the MVIC, EMG activity was acquired to normalize the EMG data

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33 collected during dynamic movements. The ri ght ankle of the participant was positioned in 5° of plantar flexion during MVIC asse ssment. One minute of rest was provided between MVIC attempts. After the maxima l torque resulting from the MVIC was determined, the participant was given a series of warm-up repetiti ons until they were familiar with the torque steadiness assessment. One minute of rest was provided prior to the actual testing. The torque steadiness test was conducted using 40% of the MVIC torque. The research particip ant was asked to maintain 40% of their MVIC torque while watching the monitor that displayed their torq ue in the form of a line that moved across the screen (Figure 3-3). Th e height of the line changed depending on how hard they pushed on the footplate. The procedures a bove were repeated for the torque steadiness test at three speeds (10°/s, 20°/s, and 30°/s) performed in a counterbalanced fashion to prevent any effect due to the order of testing with three mi nutes between speeds. Each participant completed 1 set of 10 repetitions of both CON and ECC to prevent fatigue. In addition, 10 participants from the baseline tr eatment and post treatm ent, 14 participants from the baseline control, a nd 15 participants from the pos t control groups performed the above procedures at 40°/s. After completing the Torque Steadiness Testing, the participant trained for 1-week using the same set up and procedures as the Torque Steadiness Testing. Training sessions were conducted 3 times a week, on se parate days and were the same as the testing procedure described above except that data were not record ed. The participant trained at each speed (10 /s, 20 /s, 30 /s, and 40 /s ) for 3 sets of 10 repetitions. Torque and EMG activity were measured before trai ning (BT and BC) and at the end of one week (PT and PC).

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34 Experiment 2 The second experiment involved three condi tions conducted on separate days with at least 48 hours in betwee n. The conditions were perf ormed in a counterbalanced fashion to prevent any effect due to the order of the tests. The th ree conditions included; 1) baseline (B), 2) after st retching (PS), and 3) decreased the dorsiflexion range of motion (DRM). Fifteen participants were measured as described above in the Torque Steadiness Test section for B and immediately followi ng PS or DRM. The stretching protocol involved a standard passive ankle dorsiflexion technique. Prior to stretching, the participant was set up on the Kin-Com and w ith the EMG equipment so that they could begin testing immediately after the stretching treatment. Only the test leg (right) received the treatment. During PS the participant was ly ing on his/her back (sup ine) with the left leg flexed so that their foot was in contact with the table. The st retch was performed on the test leg by passively dor siflexing the ankle of the pa rticipant. The stretch was performed (GDR) with the hip and knee of the participant flexed at 90°. The participant was instructed to remain completely relaxed during the procedure. The limb was stretched within pain free limits beyond th e normal resting length of the muscle. The stretch was held for 30 seconds and repeated for three repetitions. The stretch was applied at a low intensity for ce through the bottom of the foot of the participant. Ankle range of motion was measured immediately be fore and after the stretching procedure using the Baseline goniometer. Immediately after th e stretching the participant was set up on the Kin-Com and testing began. The decreased dorsiflexion range of motion condition was conducted using the procedures described above from the Torque Steadiness Test excep t that the range of

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35 motion was shifted to decrease the dorsifle xion (passive tension) ROM and increase plantar flexion ROM. The ROM remained 25 but was shifted to 10° of dorsiflexion, and 15° plantar flexi on (instead of 15 of plantar flexion and 10 of dorsiflexion). This was done to decrease the stretch on the Achill es tendon as the ankle was moved into dorsiflexion. In addition, 11 participan ts from each condition, baseline, decreased dorsiflexion range of motion, and after stre tch, performed the procedures at 40°/s. Data Reduction Mean torque and joint position were obtained from the Kin-Com isokinetic dynamometer in the form of ASCII data dur ing the Torque Steadiness Testing. Joint ROM from the Kin-Com AP 125 was used to sy nchronize the torque data points with the EMG activity data. A coefficient of varia tion (CV) score that represents torque steadiness was obtained by calcula ting the standard deviation of the torque divided by the mean score for each repetition. Mean torque va lues and the 40% target torque value were used to calculate error scores that represent torque steadin ess. More specifically, the absolute error score was obtained by subtrac ting the raw torque scores from the target torque the participant was attempting to maintain for that trial. The absolute value of the difference that was calculated was used so that any deviations, either positive or negative, were accounted for. For each dependent variab le measured, data were obtained from the middle 6 of the 10 repetitions that the participant performe d during the Torque Steadiness Testing. Movement detected with the electrogoniom eter was used as the starting point of EMG data collection. The intervals for each muscle action were synchronized to the torque using the Kin-Com timeline. The EMG da ta were full-wave rec tified to invert the

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36 negative deflections and add them to the positiv e deflections. Then the root mean square (RMS) of the EMG data was obtained. M ean and P/M EMG activity was obtained for the gastrocnemius and soleus during the CON/ECC. EMG data were normalized to the MVIC and reported as a per centage of maximal activa tion. P/M EMG activity was obtained by dividing the peak EMG activity by the mean EMG activity. Statistical Analyses The statistical analyses will be described in the paragraphs that follow, according to the experiment of the study. For each expe riment of the study, means and standard deviations were calculated for all variables and demographic data. A traditional level of statistical significance ( = 0.05) was used for all statistical analyses in each phase of this study. In Experiment 1 of this study the CV and absolute error scores for torque were submitted to a MANOVA (4 x 4 x 2) to determ ine the influence of treatment (BT, BC, PT and PC), velocity (10 °/s, 20°/s, 30°/s, and 40°/s) and muscle action (CON and ECC). In addition the mean EMG amplitude of the gastrocnemius and soleus, as well as, the P/M EMG amplitude of the gastrocnemius a nd soleus were analyzed using a MANOVA (4 x 4 x 2) to evaluate muscle activati on across treatment (BT, BC, PT and PC), velocities (10°/s, 20°/s, 30°/s, and 40°/s), a nd muscle action (ECC and CON). Separate univariate tests were performed and the Bonf erroni procedure was used to control the overall Type I error rate. In Experiment 2, the torque CV and absolute error scores were submitted to a MANOVA (3 x 4 x 2) to determine the in fluence of condition (B, DRM, and PS), velocity (10 °/s, 20°/s, 30°/s, and 40°/s) and muscle action (CON and ECC). In addition the RMS EMG amplitude of the gastrocnemius and soleus, as well as, the P/M EMG

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37 amplitude of the gastrocnemius and soleus were analyzed using a MANOVA (3 x 4 x 2) to evaluate muscle activation across condition (B, DRM, and PS), velocities (10°/s, 20°/s, 30°/s, and 40°/s), and muscle action (ECC a nd CON). Separate univariate tests were performed and the Bonferroni procedure was us ed to control the overall Type I error rate.

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38 CHAPTER 4 RESULTS AND DISCUSSION This study was designed to determine the e ffects of certain c onditions, contraction speeds, and muscle actions on torque steadiness as measured by plantar flexion torque and mean and P/M EMG activity of the gastrocnemius and soleus muscles during an isokinetic action. In the firs t experiment each participant completed 1-week of training and was tested on their ability to maintain a constant torque (torque steadiness) during the isokinetic CON/ECC muscle action at 10 /s, 20 /s, 30 /s, and 40 /s. Participants were tested initially and following 1-week of submax imal training at each speed. These results were compared to a control group that was matched on age and gender individually. The second experiment was designed to determin e the effects of decreasing the passive tension on the torque steadiness during the CON/ECC actions by either decreasing the dorsiflexion range of motion (DRM), or following a stretching protocol (PS). Experiment 1 Results Torque The mixed design MANOVA (Treatment x Ve locity x Muscle Action) revealed that the participants torque steadiness was a ffected by the training program, the velocity of the movement, and the type of muscle action (p<0.003). No si gnificant two-way or three-way interactions were noted for either the multivariate or when analyzing the dependent variables individually for trea tment, velocity, or muscle action. The MANOVA yielded a significant main effect for treatment (F(6,852) = 32.636, p < .001). The analysis of the individual dependent variables revealed significant

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39 differences for both the coefficient of variation (F(3,426) = 76.456, p < .001) and the absolute error (F(3,426) = 32.430, p < .001). Post -hoc analysis of the coefficient of variance and absolute error both yielded si gnificantly better torque steadiness when comparing the results of the baseline trea tment and post treatment (p < 0.001), baseline treatment and post control (p < 0.001), baseli ne control and post tr aining (p < 0.001), and post training and post control (p < 0.001) . In addition, there was a significant improvement detected by the coefficient of variance for the baseline control and post control (p < 0.001). There was no significant difference between baseline treatment and baseline control (p = 0.218) for either depende nt variable. The coefficient of variation and absolute error means for each treatment are presented in Table 4-1. Table 4-1. Mean coefficient of variati on and absolute error for each treatment. CV ABS (Nm) BT Mean .208†,‡ 14.412†,‡ SD .007 .593 PT Mean .07189†,§, 6.451†,§, SD .007 .593 BC Mean .187§,¢ 12.315§ SD .007 .564 PC Mean .126‡, , ¢ 10.965‡, SD .007 .559 Note: BT: baseline treatment; PT: post treatment; BC: baseline control; PC: post control; CV: coefficient of variation; ABS: absolute error. †Significant difference between BT and PT (p<0.05) for CV and ABS, ‡Signifi cant difference between BT and PC (p<0.05) for CV and ABS, §Significant difference be tween BC and PT (p<0.05) for CV and ABS, Significant difference between PC and PT (p<0.05) for CV and ABS, ¢Significant difference between BC and PC (p<0.05) for CV.

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40 The isokinetic torque steadi ness testing was performed at four velocities during each condition in a counterbalanced fashion. The MANOVA indicated a significant main effect for velocity (F(6,852) = 6.694, p < .001). The individual analyses revealed significant differences for both dependent vari ables including the coefficient of variation (F(3,426) = 7.655, p < .001) and the absolute error (F(3,426) = 11.799, p < .001). Posthoc analysis of the coefficient of variance and absolute error both yielded significant decreases in torque steadine ss between the 10°/s and 20°/s (p < 0.026), 10°/s and 30°/s (p < 0.004), and 10°/s and 40°/s (p < 0.001). In ad dition, there was a significant decrease in torque steadiness as determined by the abso lute error between 20° /s and 40°/s (p < 0.015). There were no other signi ficant differences among velocities. The coefficient of variation and absolute error means for each velocity are presented in Table 4-2. Table 4-2. Mean coefficient of variati on and absolute error for each velocity. CV ABS(Nm) 10°/s Mean .121†,‡,§ 8.425†,‡,§ SD .007 .559 20°/s Mean .154† 10.642†, SD .007 .559 30°/s Mean .153‡ 12.057‡ SD .007 .559 40°/s Mean .165§ 13.020§, SD .008 .630 Note: CV: coefficient of variation; ABS: absolute error. †Significant difference between 10°/s and 20°/s (p<0.05) for CV and ABS, ‡Significant difference between 10°/s and 30°/s (p<0.05) for CV and ABS, §Significant difference between 10°/s and 40°/s (p<0.05) for CV and ABS, Significant difference between 20°/s and 40°/s (p<0.05) for ABS.

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41 The MANOVA yielded a significant main effect (F(2,425) = 6.055, p = .003) for muscle action. The individual analyses revealed significant differences for both dependent variables including the coeffici ent of variation (F (1,426) = 8.758, p = .003) and the absolute error (F (1,426) = 10.268, p = .001). Th e torque steadiness was significantly worse for ECC muscle actions for the coefficient of variation and absolute error. The coefficient of variation and ab solute error means for each muscle action are presented in Table 4-3. Table 4-3. Mean coefficient of variation and absolute error for each muscle action. CV ABS(Nm) CON Mean .138† 10.111† SD .005 .408 ECC Mean .159† 11.962† SD .005 .408 Note: CV: coefficient of variation; and ABS: absolute error. †Significant difference between CON and ECC (p<0.05) for CV and ABS. Electromyography The mixed design MANOVA (Treatment x Ve locity x Muscle Action) revealed that the participants motor control as meas ured by the electrom yography of the lateral gastrocnemius and soleus was significantly aff ected by the training program, the velocity of the movement, and the type of muscle action (p<0.001). No si gnificant two-way or three-way interactions were noted for either the multivariate or when analyzing the dependent variables individually for trea tment, velocity, or muscle action. The MANOVA yielded a significant main effect for treatment (F(12,1275) = 7.779, p < .001). The individual analyses revealed significant differences for the dependent variables for the mean EMG of both musc les and for the P/M EMG ratios of both

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42 muscles. The individual analyses yielded significant increases in the lateral gastrocnemius mean EMG (F(3,426) = 7.397, p < .001), and soleus mean EMG (F(3,426) = 15.571, p < .001), and significant decreases in the lateral gastrocnemius P/M EMG (F(3,426) = 7.601, p < .001), and soleus P/ M EMG (F(3,426) = 9.552, p < .001). The lateral gastrocnemius and soleus mean EM G increased after submaximal training. Lateral gastrocnemius and soleus P/M EMG d ecreased after submaximal training. Posthoc analysis of the lateral gastrocnemius and soleus means both yielded significant increase between the baselin e treatment and post treatme nt (p < 0.022) and baseline treatment and post control (p < 0.001). In addition, there was a significant increase between the lateral gastrocnemius mean for the baseline control and post control (p < 0.020) and soleus mean for baseline c ontrol and post treatment (p<0.001). The post hoc analysis of the lateral ga strocnemius P/M EMG and soleus P/M EMG yielded significant decreases between baseline treatment and post treatment (p < 0.029), baseline treatment and baseline control (p < 0.15), and baseline treatment and post control (p < 0.001). In addition, there was a si gnificant decrease between the soleus P/M EMG for the post training and post control (p < 0.001) and baseline control and post control (p < 0.017). The lateral gastrocnem ius and soleus mean EMG and peak/mean EMG ratios for each treatment are presented in Table 4-4. The multivariate MANOVA yielded a signifi cant main effect for velocity (F(12,1275) = 7.330, p < .001). Analysis of the individual dependent variables revealed significant differences for the mean EMG a nd P/M EMG ratios of both muscles. The analyses of the individual depe ndent variables revealed significant increases in the lateral gastrocnemius mean EMG (F(3,426) = 11.106, p < .001), and soleus mean EMG

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43 (F(3,426) = 12.343, p < .001), and significant de creases in the P/M EMG (F(3,426) = 19.272, p < .001), and soleus P/M EMG (F(3,426) = 11.714, p = .001). Post-hoc analysis of the lateral gastrocnemius and soleus m ean EMG yielded significant increases between the 10°/s and 20°/s (p < 0.043), 10°/s and 30° /s (p < 0.001), 10°/s and 40°/s (p < 0.001), and 20°/s and 40°/s (p < 0.016). Table 4-4. Lateral gastrocnemius and sole us mean EMG and peak/mean EMG ratios for each treatment. LG Mean (%MVIC) LG P/M Sol Mean (%MVIC) Sol P/M BT Mean 30.717†,‡ 2.667†,‡, 36.104†,‡ 2.712†,‡, SD 2.141 .067 1.483 .071 PT Mean 39.528† 2.331† 43.929†,¢ 2.444†,£ SD 2.141 .067 1.483 .071 BC Mean 35.930§ 2.261 34.374¢ 2.469§, SD 2.037 .064 1.411 .068 PC Mean 44.108‡,§ 2.324‡ 45.749‡ 2.191‡,§,£ SD 2.019 .064 1.398 .067 Note: BT: baseline treatment; PT: post treatment; BC: baseline control; PC: post control; LG Mean: lateral gastrocnemius mean EMG; LG P/M: lateral gastrocnemius peak/mean EMG ratio; Sol Mean: soleus mean EMG; Sol P/M: soleus peak/mean EMG ratio. †Significant difference between BT and PT (p<0.05) for LG Mean, LG P/M, Sol Mean and Sol P/M, ‡Significant difference between BT and PC (p<0.05) for LG Mean, LG P/M, Sol Mean and Sol P/M, §Significant difference between BC and PC (p<0.05) for LG Mean, Sol P/M, Significant difference between BT and BC (p<0.05) for LG P/M, Sol P/M, ¢Significant difference between BC an d PT (p<0.05) for Sol Mean, £Significant difference between PT and PC (p<0.05) for Sol P/M. The post hoc analysis of the lateral ga strocnemius P/M EMG and soleus P/M EMG revealed a significant decrease between 10°/s and 30°/s (p < 0.028), 10°/s and 40°/s (p < 0.001), 20°/s and 40°/s (p < 0.001), and 30°/s and 40°/s (p < 0.011). In addition, there was a significant decrease between the latera l gastrocnemius P/M EMG for the 10°/s and

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44 20°/s (p < 0.005). The lateral gastrocnemius and soleus mean EMG and peak/mean EMG ratios for each velocity are presented in Table 4-5. Table 4-5. Lateral gastrocnemius and sole us mean EMG and peak/mean EMG ratios for each velocity. LG Mean (%MVIC) LG P/M Sol Mean (%MVIC) Sol P/M a 10°/s Mean 28.523†,‡,§ 2.748†,‡,§ 33.315†,‡,§ 2.701‡,§ SD 2.019 .064 1.398 .067 20°/s Mean 36.008†, 2.450†, 39.407†, 2.556, SD 2.019 .064 1.398 .067 30°/s Mean 41.071‡ 2.356‡,¢ 41.929‡ 2.438‡,¢ SD 2.019 .064 1.398 .067 40°/s Mean 44.680§, 2.029§, , ¢ 45.506§, 2.121§, ,¢ SD 2.273 .072 1.575 .075 Note: LG Mean: lateral gastrocnemius mean EMG; LG P/M: lateral gastrocnemius peak/mean EMG ratio Sol Mean: soleus mean EMG; Sol P/M: soleus peak/mean EMG ratio. †Significant difference between 10°/s and 20°/s (p<0.05) for LG Mean, LG P/M, and Sol Mean, ‡Significant difference betw een 10°/s and 30°/s (p<0.05) for LG Mean, LG P/M, Sol Mean and Sol P/M, §Signi ficant difference between 10°/s and 40°/s (p<0.05) for LG Mean, LG P/M, Sol Mean and Sol P/M, Significant difference between 20°/s and 40°/s (p<0.05) for LG Mean, LG P/ M, Sol Mean and Sol P/M. ¢Significant difference between 30°/s and 40°/s (p<0.05) for LG P/M, and Sol P/M. The multivariate MANOVA yielded a significa nt main effect for muscle action (F(4,423) = 46.944, p < .001). The analyses of individual dependent variables revealed significant differences for the dependent variables for the mean EMG of both muscles and for the P/M EMG ratios of both muscles. The individual analyses revealed a significant difference between the lateral ga strocnemius mean EMG (F(1,426) = 5.323, p = .022), soleus mean EMG (F(1,426) = 140.770, p < .001), lateral gastrocnemius P/M EMG (F(1,426) = 26.808, p < .001), and so leus P/M EMG (F(1,426) = 102.400, p <

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45 .001). Mean EMG during the ECC was signifi cantly lower than CON for the lateral gastrocnemius and the soleus. Peak/mean EMG was significantly greater for the ECC lateral gastrocnemius and soleus. The late ral gastrocnemius and soleus mean EMG and peak/mean EMG ratios for each muscle action are presented in Table 4-6. Table 4-6. Lateral gastrocnemius and soleus means and peak/mean ratios for each muscle action. LG Mean(%MVIC) LG P/M Sol Mean(%MVIC) Sol P/M CON Mean 39.976† 2.226† 48.608† 2.104† SD 1.475 .046 1.021 .049 ECC Mean 35.165† 2.566† 31.470† 2.805† SD 1.475 .046 1.021 .049 Note: LG Mean: lateral gastrocnemius mean EMG; LG P/M EMG: lateral gastrocnemius peak/mean EMG ratio Sol Mean: soleus mean EMG; Sol P/M: soleus peak/mean EMG ratio. †Significant difference between CON and ECC (p<0.05) for LG Mean, LG P/M, and Sol Mean. Experiment 2 Results Torque Experiment 2 involved two conditions; decr easing the dorsiflexion range of motion of the isokinetic movement and after stretching compared to a baseline measurement. To determine the effectiveness of the stretching protocol the range of motion of the ankle was measured preand post-st retch. Ankle dorsiflexion si gnificantly increased (p = 0.007) by 4° while the plantar flexion range of motion did not change. The mixed design MANOVA (Condition x Velocity x Muscle Action) revealed that the conditions and the velocity of the m ovement significantly affected the torque steadiness (p<0.003). There was no significan t main effect for muscle action as determined by the MANOVA. No significant tw o-way or three-way interactions were

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46 noted for either the multivariate or when an alyzing the dependent va riables individually for condition, velocity, or muscle action. The MANOVA yielded a significant main effect for condition (F(4,624) = 4.036, p = .003). The individual analyses revealed a significant difference only for the absolute error (F(2,312) = 5.329, p = .005) bu t not for the coefficient of variation. The coefficient of variation was greater fo r the decreased dorsiflexion range of motion condition and after stretching compared to the baseline. The absolute error score for the decreased dorsiflexion range of motion component was greater than baseline and after stretching was greater than baseline. Post-hoc analys is of the absolute error score yielded a significant difference between the baseline condition and after stretching (p = 0.005). The coefficient of variation and absolute error score means for each condition are presented in Table 4-7. The MANOVA yielded a significant main effect for velocity (F(6,624) = 3.575, p = .002). The individual analyses revealed si gnificant differences for both dependent variables including the coefficient of va riation (F(3,312) = 4.569, p = .004) and the absolute error (F(3,312) = 5.319, p = .001). The velocity of the isokinetic movement revealed that the torque stead iness was significantly better for the 10°/s than either 20°/s, 30°/s, or 40°/s as measured by the coefficien t of variation, and betw een 10°/s and either 30°/s, or 40°/s for the absolute error scores. Post-hoc anal ysis of the coefficient of variance and absolute error both yielded signi ficant increases between the 10°/s and 30°/s (p < 0.018), and 10°/s and 40°/s (p < 0.033). In addition, there was a significant increase between the coefficient of variation for 10°/s and 20°/s (p < 0.016). There were no other

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47 significant differences among velocities. The co efficient of variation and absolute error means for each velocity are presented in Table 4-8. Table 4-7. Mean coefficient of varia tion and absolute error for each condition. CV ABS (Nm) B Mean .136 8.437† SD .008 .533 DRM Mean .140 9.224 SD .008 .533 PS Mean .143 10.851† SD .008 .533 Note: B: baseline; DRM: decreased dorsifle xion range of motion; PS: post stretch; CV: coefficient of variation; ABS: absolute erro r. †Significant difference between B and PS (p<0.05) for ABS. The MANOVA for muscle action yielded no significant main effect (F(2,311) = 0.761, p = .468). The coefficient of variation and absolute error means for each muscle action are presented in Table 4-9. Electromyography The mixed design MANOVA (Condition x Velocity x Muscle Action) revealed that the participants’ motor control as measur ed by the electromyography of the lateral gastrocnemius and soleus was significantly aff ected by the velocity of the movement, and the type of muscle action (p<0.001). In addi tion, the ratio of peak EMG to mean EMG was significantly affected by the velocity and muscle action (p<0.001). There was no significant main effect for condition as determined by the MANOVA. In addition, no significant two-way or three-way interactions were noted for either the multivariate tests

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48 or when analyzing the dependent variables in dividually for condition, velocity, or muscle action. Table 4-8. Mean coefficient of variati on and absolute error for each velocity. CV ABS (Nm) 10°/s Mean .111†,‡,§ 7.578‡,§ SD .009 .590 20°/s Mean .149† 9.435 SD .009 .590 30°/s Mean .151‡ 10.018‡ SD .009 .590 40°/s Mean .148§ 10.986§ SD .010 .689 Note: CV: coefficient of variation; and ABS: absolute error. †Significant difference between 10°/s and 20°/s (p<0.05) for CV, ‡Significant difference between 10°/s and 30°/s (p<0.05) for CV and ABS, §Significant difference between 10°/s and 40°/s (p<0.05) for CV and ABS. The MANOVA yielded no significant main effect for condition (F(8,620) = 1.010, p < .427). The lateral gastrocnemius and so leus mean EMG and peak/mean EMG ratios for each condition are presented in Table 4-10. The MANOVA yielded a significant main effect for velocity (F(12,933) = 4.450, p < .001). The individual analyses revealed significant differences for the dependent variables for the means of both muscles and for the P/M EMG ratios of both muscles. The individual analyses revealed significan t differences for lateral gastrocnemius mean EMG (F(3,312) = 4.559, p = .004), soleus mean EMG (F(3,312) = 3.338, p = .020), lateral gastrocnemius P/M EMG (F(3,312) = 13.962, p < .001), and soleus P/M EMG (F(3,312) = 7.127, p < .001). The mean EMG re sults were greater when comparing

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49 velocities 30°/s and 40°/s to 10° /s for the lateral gastrocnemius, and greater at 30°/s than 10°/s for the soleus. Also, the P/M EMG re sults were less when comparing velocities 30°/s and 40°/s to 10°/s for th e lateral gastrocnemius, and le ss for 30°/s than 10°/s for the soleus. In addition, 40°/s were less than 20° /s for the lateral gastrocnemius and soleus P/M EMG respectively. Post-hoc analysis of the lateral gastrocnemius and soleus mean EMG both yielded significant increases between the 10°/s and 30°/s (p < 0.020). In addition, the lateral gastrocnemius mean EM G was significantly greater for 10°/s and 40°/s (p < 0.014). Table 4-9. Mean coefficient of variation and absolute error for each muscle action. CV ABS (Nm) CON Mean .136 9.124 SD .007 .435 ECC Mean .144 9.884 SD .007 .435 Note: CV: coefficient of variation; and ABS: absolute error. The post hoc analysis of the lateral ga strocnemius P/M EMG and soleus P/M EMG revealed significant less between 10°/s and 40°/s (p < 0.001), and 20°/s and 40°/s (p < 0.004). In addition, there was a significant de crease between the lateral gastrocnemius P/M EMG for the 10°/s and 30°/s (p < 0.001). The lateral gastrocnemius and soleus mean EMG and peak/mean EMG ratios for each velocity are presented in Table 4-11.

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50 Table 4-10. Lateral gastrocnemius and sole us mean EMG and peak/mean EMG ratios for each condition. LG Mean (%MVIC) LG P/M Sol Mean (%MVIC) Sol P/M B Mean 30.094 2.663 37.652 2.607 SD 1.816 .080 1.426 .083 DRM Mean 33.390 2.827 39.655 2.608 SD 1.816 .080 1.426 .083 PS Mean 31.842 2.594 38.517 2.599 SD 1.816 .080 1.426 .083 Note: B: baseline; DRM: decreased dorsifle xion range of motion; PS: post stretch; LG Mean: lateral gastrocnemius mean EMG; LG P/M: lateral gastrocnemius peak/mean EMG ratio; Sol Mean: soleus mean EMG; Sol P/M: soleus peak/mean EMG ratio. The MANOVA yielded a significant main effect for muscle action (F(4,309) = 30.809, p < .001). The individual analyses reve aled significant differences for the dependent variables for the mean EMG of both muscles and for the P/M EMG ratios of both muscles. The individual analyses re vealed significant differences for lateral gastrocnemius mean EMG (F(1,312) = 10.121, p = .002), soleus mean EMG (F(1,312) = 78.704, p < .001), lateral gastrocnemius P/M EMG (F(1,312) = 32.979, p < .001), and soleus P/M EMG (F(1,312) = 57.166, p < .001). Mean EMG during the ECC was significantly lower than CON for the lateral gastrocnemius and the soleus. Peak/mean EMG was significantly greater for the ECC late ral gastrocnemius and soleus. The lateral gastrocnemius and soleus mean EMG and peak /mean EMG ratios for each muscle action are presented in Table 4-12.

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51 Table 4-11. Lateral gastrocnemius and sole us mean EMG and peak/mean EMG ratios for each velocity. LG Mean(%MVIC) LG P/M Sol Mean(%MVIC) Sol P/M 10°/s Mean 26.376†,‡ 3.101†,‡ 34.437† 2.876‡ SD 2.008 .089 1.576 .092 20°/s Mean 29.885 2.852§ 38.709 2.721§ SD 2.008 .089 1.576 .092 30°/s Mean 35.211† 2.530† 40.878† 2.575 SD 2.008 .089 1.576 .092 40°/s Mean 35.630‡ 2.295‡,§ 40.408 2.246‡,§ SD 2.345 .104 1.840 .107 Note: LG Mean: lateral gastrocnemius mean EMG; LG P/M: lateral gastrocnemius peak/mean EMG ratio; Sol Mean: soleus mean EMG; Sol P/M: soleus peak/mean EMG ratio. †Significant difference between 10°/s and 30°/s (p<0.05) for LG Mean, LG P/M, and Sol Mean, ‡Significant difference betw een 10°/s and 40°/s (p<0.05) for LG Mean, LG P/M, and Sol P/M, §Significant differen ce between 20°/s and 40°/s (p<0.05) for LG P/M, and Sol P/M. Table 4-12. Lateral gastrocnemius and sole us mean EMG and peak/mean EMG ratios for each muscle action. LG Mean(%MVIC) LG P/M Sol Mean(%MVIC) Sol P/M CON Mean 35.111† 2.428† 45.910† 2.243† SD 1.483 .066 1.164 .068 ECC Mean 28.440† 2.961† 31.306† 2.966† SD 1.483 .066 1.164 .068 Note: LG Mean: lateral gastrocnemius mean EMG; LG P/M: lateral gastrocnemius peak/mean EMG ratio; Sol Mean: soleus mean EMG; Sol P/M: soleus peak/mean EMG ratio. †Significant difference between CON and ECC (p<0.05) for LG Mean, LG P/M, Sol Mean, and Sol P/M.

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52 CHAPTER 5 DISCUSSION AND CONCLUSIONS Muscle strain injuries in athletic competition account for between 10 and 55% of all injuries (Jarvinen et al., 2000). These muscle strain injuries frequently occur in muscle fibers near the musculotendious j unction and often occur in two joint muscles during eccentric muscle actions (Jarvinen et al., 2000; Garrett, 1996), which are a crucial part of almost every type of athletic pe rformance. Eccentric muscle actions are controlled by different neural st rategies than concentric muscle actions as is evident in the EMG activity (Tesch et al., 1990; Nardone et al., 1988). Eccentric muscle actions require lower levels of voluntary activati on than concentric muscle actions as demonstrated by lower levels of EMG activ ity. This decreased mean EMG activity during eccentric muscle actions has been related to a protective, tension limiting mechanism (Enoka, 1996). Eccentric muscle act ions have also been associated with greater motor-unit synchronization than concentric muscle actions. This is evident in the greater EMG activity observed in the increased peaks. The purpose of this study was to investigate the response of the torque steadiness and the neural control of concentric and eccentric muscle actions to injury prevention and treatment techniques. The specific aims and discussion for each phase of the proposed project follow: Experiments 1 and 2 1. To determine if increasing velocity will decrease torque steadiness. Torque steadiness decreased with in creasing velocities greater than 10 /s as measured by both the coefficient of variati on and the absolute error. These results

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53 indicate the torque steadiness for the 10 /s speed was significantly better than the faster speeds. As the velocity of the movement increases the time during each phase, CON and ECC, decreases. With a decrease in time for feedback and corrections, the torque steadiness would be expected to diminish (Komi et al., 1997; and Enoka, 1996). This could also be explained because as the velo city of the movement increases, the time to create the contraction for a gi ven torque/force decr eases; therefore the amount of muscle force necessary to sustain the torque/force woul d need to increase. This is consistent with conclusion from Bishop et al. (2000), Arnold et al. (199 7), and Enoka (1996), that as the velocity of the muscle action increases, especially during concen tric muscle action, the amount of muscle tension that can be achie ved decreases. Theref ore, as the velocity of the movement increases, more motor units need to be recruited to maintain the constant torque during the tor que steadiness testing. As a result, the torq ue steadiness would be expected to decrease with increasing velocity. 2. To determine if increasing velocity would increase the mean EMG activity for the plantar flexors. The results of this experiment are consis tent with Bigland et al. (1954) that the mean EMG activity increased with increasing velocity. The mean EMG activity increase can be explained because as the velocity of the movement increases, the time to create the contraction for the target tor que/force decreases. Therefor e the amount of muscle force necessary to sustain the constant to rque/force would need to increase. 3. To determine if increasing velocity would decrease the ratio of peak to mean EMG activity for the plantar flexors. The P/M EMG ratio in the present investig ation decreased with increasing velocity owing to the effect of the increase in mean EMG on the ratio. In addition, these findings are consistent with Semmler et al. (2002) that motor unit synchronization is enhanced

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54 during slow lengthening contrac tions. Therefore, the greatest peaks, and therefore P/M EMG activity ratio, would occur at the slower velocities. The results related to neural control strate gies in this investig ation provide insight into the motor unit synchroniza tion during relatively slow ve locities. However, muscle injuries frequently occur with greater velo cities, therefore, fu ture research should investigate the effects of higher velo cities on neural control strategies. Experiment 1 4. To determine if submaximal training would increase torque steadiness. One technique used to prevent and treat muscle strain injuries has been muscle strengthening through re sistance training (Best et al., 1996; Garrett, 1996). Early changes to muscle following maximal resistance training result primarily from increases in improvements in neural efficiency (Higbie et al., 1996; Sale, 1988) . However, these changes in neural efficiency have been disputed (Higbie et al., 1996; Thorstensson et al., 1976; Sale et al. 1988). In addition, the e ffects of submaximal training on torque steadiness and neural control has not yet been investigated. The results of this experiment revealed that the submaximal training improved torque steadiness as measured by the coefficient of variation and the ab solute error score. Bilodeau et al. (2000) also reported improved steadiness in individuals wi th essential tremors following resistance training. Thes e findings are countered by the results of Bishop et al. (2000), who observed an increase in torque variability following training. However, this discrepancy can be explained by the fact that participants in their study performed maximal eccentric training for a th ree-week period whereas in the present study the improvement in torque steadiness wa s the result of the one-week submaximal training. In addition to these findings, there appeared to be an improvement in torque

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55 steadiness related to a learning effect in the present study si nce torque steadiness in the control group also improved. However, th e torque steadiness of the treatment group improved significantly more than the contro l group. These findings suggest that the training protocol was effective in improving torque steadiness. 5. To determine if submaximal training w ould increase mean EMG activity of the plantar flexor muscles. The EMG activity of the lateral gastrocnemius and soleus in general responded similarly revealing increases in mean EMG. These results were similar to those reported previously in studies in which participants demonstrated an increase in EMG activity after performing maximal resistance training (Seger, & Thorstensson, 2005; Higbie et al., 1996; Hortobagyi et al., 1996; Hakkinen et al., 1983). It is assumed that this demonstrates that the training resulted in an improvement in muscle activation or an increase in the number of motor units recruited. 6. To determine if submaximal training woul d decrease the ratio of peak to mean EMG activity of the plantar flexor muscles. The results of the present study indicate th at the P/M EMG ratio decreased for both muscles following training. This decrease in P/M EMG ratio is an indication of a decrease in motor unit synchronization or may be reflective of an increase in the mean EMG activity. Burke et al. (1978) reporte d that motor-unit s ynchrony increases EMG activity causing greater peaks. Milner-Brown et al. (1975) re ported lower levels of motor unit synchronization in the hands of skill-trained indi viduals. With a decrease in the peak EMG, it would be assumed that the muscle spindle afferent feedback would increase resulting in an improvement efficiency of mu scle contraction. By more fully activating the muscle, the participant may have great er control over the movement. This is consistent with Docherty et al. (1998) who reported improved joint position sense

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56 following resistance training of functionally unstable ankles. They theorized that improvements in joint angle were related to the muscle spindle -efferent activity causing the muscle spindle to be more sensitive to stretch resulting in the greater ankle joint position sense. These findings are in cont rast to Bishop et al. (2000) who found an increase in the ratio of P/M EMG activity with maximal resistance training. This may be explained because the particip ants in the present study trai ned using submaximal torque steadiness training. 7. To determine if submaximal training w ould improve the torq ue steadiness during the ECC. 8. To determine if submaximal training would decrease the ratio of the peak to mean EMG activity of the plantar flexor muscles during the ECC. Torque steadiness was significantly worse in this investigation during the ECC than the CON. As was theorized previously, this appears to be related to a greater amount of motor unit synchronization during the ECC as demonstrated by the greater P/M EMG activity ratio in both muscles. This is c onsistent with findings by Bishop et al. (2000), Tesch et al. (1990), Nardone et al. (1988), and Burke et al. (1978) who determined that ECC resulted in greater moto r unit synchronization. Yao et al. (2000), concluded that motor-unit synchrony increases the amplitude of force fluctuations and therefore a decrease in torque steadiness. These spikes ar e thought to be the result of higher levels of spindle afferent feedback causing more sync hronization of motor unit activation during ECC. Eccentric muscle actions result in the activation of high-thres hold motor units with large-amplitude action potentials compar ed to CON and cause greater motor unit synchronization (Howell et al., 1995). Eccentric muscle actions result in a gr eater number of muscle strain injuries, however the reason is unclear. It is believed that the increased number of injuries during

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57 ECC is the result of the neural control mech anism that includes a decreased mean EMG activity and a greater amount of motor unit synchronization. The results indicate that ECC torque steadiness did not improve and mu scle activity did not increase. However, since the training protocol re sulted in an overall improvement in the torque steadiness and increase in muscle activity as was explai ned previously in specific aims 4-6, it is possible that the submaximal training protoc ol resulted in an improvement in both CON and ECC. It can be concluded that the submaximal training did not affect the ECC enough to improve the torque steadiness and increase the muscle activity to a similar level as CON, however, the overall affect of the training protocol may have improved both CON and ECC. Since the training prot ocol improved the combination of eccentric muscle actions and concentric muscle acti ons, it appears that submaximal CON/ECC training may be a beneficial t echnique for preventing and treat ing muscle strain injuries and should be investigated further. 9. To determine if submaximal training would increase the mean EMG activity of the plantar flexor muscles during the ECC. The mean EMG during ECC was significantl y less than CON. These findings are consistent with other findings that ECC re quire lower levels of voluntary activation as demonstrated by lower levels of EMG activ ity than CON (Enoka, 1996; Nardone et al., 1988; Burke et al., 1978). The lower levels of EMG activity during ECC provide further evidence that ECC recruits less motor units th at limits the amount of tension within the muscle. By recruiting fewer motor units, th is appears to be protective in nature by allowing damage to fewer muscle fibers.

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58 Experiment 1 Conclusions Eccentric muscle actions are a critical pa rt of most athletic movements and are frequently related to muscle strain injuries. As a result, these muscle actions have been the focus of a great deal of recent research. However, there is still little understanding about the control of eccentric muscle actions or how they are linked to muscle strain injuries. The present experiment was an atte mpt to investigate the control of eccentric muscle actions and their response to submaxim al torque steadiness training. The overall results from this experiment indicate that one-week of submaxim al torque steadiness training improved torque steadiness, increas ed mean EMG and decreased P/M EMG. This suggests an overall improvement in moto r unit synchronization, a factor associated with muscle strain injuries. As the veloci ty of the isokinetic ac tion increased from 10 /s, the torque steadiness decreased, mean EMG increased and P/M EMG decreased. Finally, eccentric muscle actions were associated with a significant decrease in torque steadiness, a decrease in mean EMG and an increase in P/M EMG. Since the tr aining protocol did improve the overall torque st eadiness and muscle activity, it appears that submaximal CON/ECC training may be benefi cial in preventing and treati ng muscle strain injuries. Experiment 2 Little is known about the potential predis posing factors that cau se muscle strains (Best et al., 1996). Factors such as fati gue, poor flexibility, and a low agonist-toantagonist strength ratio have been suggested to increase susceptibility to muscle strain injuries (Brockett et al., 2004). Recently, there have been di screpancies in the literature as to the effectiveness of st retching on injury prevention (Bro ckett et al., 2004; Thacker et al., 2004). In addition, there is little information describing the effects of stretching in injury prevention and on muscle control. It has been demonstrated that stretching may

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59 have a negative effect on performance, speci fically power types of activities (Cornwell et al., 2002; Kokkonen et al., 1998). Two mechanisms are believed to be responsible for the effect of stretching on performa nce and muscle power; 1) decrease in muscle stiffness, and 2) a depression in muscle activation as a result of Golgi tendon inhibition (Guissard et al., 2004; Kokkonen et al., 1998). Therefore, experiment 2 was designed to investigate the effect of changing muscle stiffness by decreasing the dorsiflexion range of motion. By decreasing the dorsiflexion range of motion the passive te nsion in the muscle would be decreased as demonstrated by the stress strain relationship and may decrease torque steadiness. In addition, experiment 2 was desi gned to influence both muscle stiffness and the neural mechanisms post stretch and may also result in a decrease in torque steadiness. 10. To determine if the passive stretching pr otocol increased ankl e dorsiflexion range of motion. The static stretching technique used in this study resulted in a significant increase in passive ankle dorsiflexi on range of motion as measured in this experiment. 11. To determine if decreasing the dorsiflex ion range of motion or stretching would decrease torque steadiness. Since the stretching protocol resulted in an increase in ankle dorsi flexion, as stated previously, this may result in a decrease in muscle stiffness (Cornwell et al., 2002; Kokkonen et al., 1998) and/or a depression in mu scle activation as a result of the Golgi tendon inhibition (Guissard et al., 2004; Kokkonen et al., 1998). The results of this study i ndicate that there was no si gnificant difference in torque steadiness post stretch as measured by the coe fficient of variation, bu t the absolute error score was worse. The coefficient of varia tion is calculated by dividing the standard deviation by the mean for each trial. The abso lute error score is determined by taking the average of the absolute difference scores betw een the actual torques subtracted from the

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60 target torque during an entir e trial. Although the coeffici ent of variation is a better measure of torque steadiness, the absolute error score can determine participants who may be more steady but not able to achieve the target torque, either above or below. Post stretch was significantly worse than baseline as measured by the absolute error score, whereas the decreased dorsiflexion ra nge of motion condition was not significantly different than baseline. It was thought that by modifying movement parameters so that subjects were tested away from the end of joint ROM, contribution of passive tension from the series elastic com ponent of the plantar flexor muscles would be decreased (Figure 5-1) (Hall, 2003). However, this was not reflected in the coefficient of variation or the absolute error scores for the decrease d dorsiflexion range of motion. This may be explained because the amount of active muscle activity did not increase to a high enough intensity during the submaximal torque steadin ess testing to affect the neural feedback from the golgi tendon organs in the muscle as post stretching would. Since the stretch reflex involves feedback from the golgi tendon organs, this may have resulted in an effect on the participantÂ’s ability to maintain th e target torque (Gui ssard et al., 1998). The effects of stretching on performance, or absolute error scor es in this study, are consistent with Cornwell et al. (2002) who found that stretching resulted in a decrease in countermovement jump height following stre tching. Their results could not rule out either mechanism as the factor in decreased performance, either muscle stiffness or depression of muscle activation. They did how ever conclude that the change in muscle stiffness, as measured by a non-invasive ca lculation, was small but significant. The results of the present study were designed to be more easily interpreted since the isokinetic CON/ECC is less dynamic than the countermovement jump (Cornwell et al.,

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61 2002). In addition, the results of the present study are consistent with Cornwell et al. (2002) in that the decreased dorsiflexion range of motion, or muscle stiffness, may not have been enough to affect the torque steadin ess. However, the combined effect of decreasing the dorsiflexion range of motion a nd the depressed neural feedback may have affected the absolute error scores in the present study in the post stretch condition. Figure 5-1. Length tension relationship of muscle (adapted from Hall, 2003) 12. To determine if decreasing the dorsiflex ion range of motion or stretching would affect the mean EMG activity or the rati o of peak to mean EMG activity of the ankle plantarflexors. There was no significant difference between the mean EMG or P/M EMG ratio for the conditions in this experiment. These results are consistent with other findings (Cornwell et al., 2002). Decreasing the dor siflexion range of motion as in this investigation does not affect the muscle activ ation. In addition, the post stretch condition did not affect muscle activation. This may be because the submaximal torque did not

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62 result in enough force in the muscle to activ ate the golgi tendon orga ns and result in an alteration in the neural feedback. 13. To determine if decreasing the dorsiflex ion range of motion or stretching would improve torque steadiness during ECC. Torque steadiness as measured by the coefficient of variation and absolute error was not significantly affected by the muscle action, either CON or ECC. The results do reveal that the coefficient of variation and th e absolute error scores are greater for ECC, but not significantly. This is consistent w ith previous findings in this study and by Bishop et al., (2000) that ECC were less steady than CON. 14. To determine if decreasing the dorsiflex ion range of motion or stretching would affect the mean EMG activity of th e ankle plantar flexors during ECC. The mean EMG activity during ECC was si gnificantly less than CON. These findings are consistent with other findings and experiment one of this study (Enoka, 1996; Nardone et al., 1988; Burke et al., 1978). 15. To determine if decreasing the dorsiflex ion range of motion or stretching would affect the ratio of the peak to mean EMG activity of the ankle plantar flexors during ECC. The ECC P/M EMG activity ratio was significantly greater for both muscles than CON. The greater P/M EMG implies a gr eater amount of motor unit synchronization during the ECC or a smaller mean EMG activity consistent with fi ndings by Bishop et al., 2000; Tesch et al., 1990; Nardone et al., 1988; and Burke et al., 1978. Yao et al. (2000) reported that motor-unit synchrony increases the amplitude of force fluctuations and therefore a decrease in torque steadiness. The findings in the present experiment are similar to experiment one.

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63 Experiment 2 Conclusions Experiment 2 was designed to investigate the effect of changing muscle stiffness by decreasing the dorsiflexion range of motion and by influencing the neural mechanisms post-stretching. The combined effect of decreasing the muscle stiffness and the depressed neural feedback may have affected the absolute error scores in the present study in the post stretch condition. However, decreasing the passive tension or the stiffness of the muscle alone did not affect performance. Therefore, post stretching appears to have an influential on motor co ntrol and may affect muscle performance during athletic activities. Future Research The findings in these experiments provid e additional information about torque steadiness and the neural control of eccentric muscle actions. Future research should investigate the effects of other muscle strain injury prevention t echniques, the use of more functional velocities, and the use of othe r muscles/joints affects on these variables. In addition, future studies s hould investigate torq ue steadiness and ne ural control of eccentric muscle actions for other patient populations including individuals with functional ankle instability, patients with muscle strain injuries, neur ological disorders, and elderly populations.

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64 APPENDIX A UNIVERSITY OF FLORIDA INSTITUTIONAL REVIEW BOARD INFORMED CONSENT Informed Consent Protocol Title : Tension Regulation During Eccentric Actions. Phase I Please read this consent document carefully before you decide to participate in this study. Purpose of the research study : The purpose of this study is to investigat e tension regulation during eccentric actions (ECC). Tension regulation is a measure of your ability to maintain a constant force. An eccentric action happens when your muscle le ngthens while it contracts (like when you are lowering something down). This study wi ll specifically attempt to determine the passive component of eccentric actions. The passive component of the eccentric action is the part of your muscle th at is able to stretch. Eccentric actions are very common muscle c ontractions that occur during activities of daily living as well as during athletic competition. Our understanding of eccentric muscle actions can help us learn more about how people are injured and how to manage their injuries th rough rehabilitation. What you will be asked to do in this study : The tension regulation test will be done using a machine called the Kin Com (Chattanooga, TN) testing device. The Kin Co m testing device will be used to test the strength of your ankle while it moves your a nkle up and down. You will be asked to sit on the Kin Com and positioned according to ma nufacturers instructi ons with your foot fastened to a footplate. You will be given a series of warm-up repetitions to familiarize you with the motion to be tested. After th e warm-up session is completed and you feel comfortable with the testing procedure you w ill be asked to remain completely relaxed while the footplate moves through the motion to be tested. After this, you will be asked to perform 3 maximal contractions. To perform the maximal contraction, you will be asked to push down on the footplate as hard as possible like pushing on a gas pedal. You will be given 30 seconds to rest between maximal contra ctions. After the maximal test you will be asked to watch the computer mo nitor to try to maintain a line that moves across the screen at a constant height. Th e height of the line changes depending on how hard you push on the footplate. When you feel comfortable maintaining the line at its height you will then be asked to relax. After you rest and when you are ready to start, the submaximal test will begin. The submaximal test will be done with the footplate moving

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65 at three slow speeds. You will be asked to push against the footplate, like pushing on a gas pedal, while the footplate moves. During the testing, your muscle act ivity will be measured usin g EMG. The tester will put electrodes on the surface of your skin over your lower leg muscles. The EMG picks up muscle activity and does not send any electr ical activity into your body. You will not feel any sensation with the use of EMG. Time required : 45 minutes per session Potential Benefits a nd Anticipated Risks : There are no more than minimal risks associ ated with this stu dy. You should consult with a physician if you are unsure whether you ca n participate in this study. If you are injured during this study as a result of the negligence of the princi pal investigator, the University of Florida, the Board of Regent s of the State of Florida and the State of Florida shall be liable only as provided by law. You may seek appropriate compensation for injury by contacting the Insurance Coordina tor at 316 Stadium, University of Florida, (352) 392-2556. We do not anticipate that you will benefit directly by participating in this experiment. Compensation : You will not receive any compensa tion for completing this study. Confidentiality : Your identity will be kept confidential to the extent provided by law. Your information will be assigned a code number. The list c onnecting your name to this number will be kept in a locked file in my faculty supervisorÂ’s office. 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 in this study is complete ly voluntary. There is no penalty for not participating. Right to withdraw from the study : You have the right to withdraw from this study at any time without consequence. You are free to quit any exercise at any time, especially so as to prevent an injury.

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66 Whom to contact if you have questions about the study Gerard D. Rozea, MS, ATC/L, Graduate St udent, Department of Exercise and Sport Science, 100 Florida Gym, 392-0584 x 1402 Current address: Department of Health Science, 115 Himes Ha ll, Lock Haven University, Lock Haven, PA 17745, Phone (570) 893-2294, email: grozea@lhup.edu Mark Tillman, PhD, Assistant Professor, Depa rtment of Exercise and Sport Science, 100 Florida Gym, Phone 392-9575 x1237, email: mtillman@hhp.ufl.edu Whom to contact about your rights as a research participant in the study : UFIRB Office, Box 112250, University of Fl orida, Gainesville, FL 32611-2250; ph 3920433. 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: _______________

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67 Informed Consent Protocol Title : Tension Regulation During Eccentric Actions. Phase II Purpose of the research study : The purpose of this study is to investigat e tension regulation during eccentric actions (ECC). Tension regulation is a measure of your ability to maintain a constant force. An eccentric action happens when your muscle le ngthens while it contracts (like when you are lowering something down). This study wi ll specifically attempt to determine the effects of 1) stretching, and 2) decreased passive component on tension regulation during ECC. Eccentric actions are very common musc le contractions that occur during activities of daily living as well as during athletic competition. Our understanding of eccentric muscle actions can help us learn more about how people are injured and how to manage their injuries th rough rehabilitation. What you will be asked to do in this study : Tension regulation during eccentric actions will be performed using the Kin Com (Chattanooga, TN) testing device. The Kin Co m testing device will be used to test the strength of your ankle while it moves your a nkle up and down. You will be asked to sit on the Kin Com and positioned according to ma nufacturers instructi ons with your foot fastened to a footplate. You will be given a series of warm-up repetitions to familiarize you with the motion to be tested. After th e warm-up session is completed and you feel comfortable with the testing procedure you w ill be asked to remain completely relaxed while the footplate moves through the motion to be tested. After this, you will be asked to perform 3 maximal contractions. To perform the maximal contraction, you will be asked to push down on the footplate as hard as possible like pushing on a gas pedal. You will be given 30 seconds to rest between maximal contra ctions. After the maximal test you will be asked to watch the computer monitor to try maintain a line that moves across the screen at a constant height. Th e height of the line changes depending on how hard you push on the footplate. When you feel comfortable maintaining the line at its height you will then be asked to relax. After you rest and when you are ready to start, the submaximal test will begin. The submaximal test will be done with the footplate moving at three slow speeds. You will be asked to push against the footplate, like pushing on a gas pedal, while the footplate moves. During the testing, your muscle act ivity will be measured usin g EMG. The tester will put electrodes on the surface of your skin over your lower leg muscles. The EMG picks up muscle activity and does not send any electr ical activity into your body. You will not feel any sensation with the use of EMG. You will be asked to undergo the same testing procedure described above before and immediately after 2 treatments: 1) stretc hing, and 2) decreased passive component. During the stretching we will st retch only on leg. You will be asked to lie on your back. You will be asked to remain completely rela xed during the procedure. Your limb will be

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68 stretched within pain free limits. The stretch will be held for 30 seconds and repeated for three repetitions. The decreased passive com ponent will be performed the same as the baseline measurement except the range of motion will involve less dorsiflexion and more plantarflexion. The stretching and decreased passive component treatments will be performed on separate days. Time required : 45 minutes per session Potential Benefits a nd Anticipated Risks : There are no more than minimal risks associ ated with this stu dy. You should consult with a physician if you are unsure whether you ca n participate in this study. If you are injured during this study as a result of the negligence of the princi pal investigator, the University of Florida, the Board of Regent s of the State of Florida and the State of Florida shall be liable only as provided by law. You may seek appropriate compensation for injury by contacting the Insurance Coordina tor at 316 Stadium, University of Florida, (352) 392-2556. We do not anticipate that you will benefit directly by participating in this experiment. Compensation : You will not receive any compensa tion for completing this study. Confidentiality : Your identity will be kept confidential to the extent provided by law. Your information will be assigned a code number. The list c onnecting your name to this number will be kept in a locked file in my faculty supervisorÂ’s office. 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 in this study is complete ly voluntary. There is no penalty for not participating. Right to withdraw from the study : You have the right to withdraw from this study at any time without consequence. You are free to quit any exercise at any time, especially so as to prevent an injury.

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69 Whom to contact if you have questions about the study Gerard D. Rozea, MS, ATC/L, Graduate St udent, Department of Exercise and Sport Science, 100 Florida Gym, 392-0584 x 1402 Current address: Department of Health Science, 115 Himes Ha ll, Lock Haven University, Lock Haven, PA 17745, Phone (570) 893-2294, email: grozea@lhup.edu Mark Tillman, PhD, Assistant Professor, Depa rtment of Exercise and Sport Science, 100 Florida Gym, Phone 392-9575 x1237, email: mtillman@hhp.ufl.edu Whom to contact about your rights as a research participant in the study : UFIRB Office, Box 112250, University of Fl orida, Gainesville, FL 32611-2250; ph 3920433. 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: _______________

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70 Informed Consent Protocol Title : Tension Regulation During E ccentric Actions. Phase III Purpose of the research study : The purpose of this study is to investigat e tension regulation during eccentric actions (ECC). Tension regulation is a measure of your ability to maintain a constant force. An eccentric action happens when your muscle le ngthens while it contracts (like when you are lowering something down). This study wi ll specifically attempt to determine the effects of 2 weeks of training on tension re gulation during ECC. Eccentric actions are very common muscle contracti ons that occur duri ng activities of daily living as well as during athletic competition. Our understanding of eccentric muscle actions can help us learn more about how people are injured a nd how to manage their injuries through rehabilitation. What you will be asked to do in this study : Tension regulation during eccentric actions will be performed using the Kin Com (Chattanooga, TN) testing device. The Kin Co m testing device will be used to test the strength of your ankle while it moves your a nkle up and down. You will be asked to sit on the Kin Com and positioned according to ma nufacturers instructi ons with your foot fastened to a footplate. You will be given a series of warm-up repetitions to familiarize you with the motion to be tested. After th e warm-up session is completed and you feel comfortable with the testing procedure you w ill be asked to remain completely relaxed while the footplate moves through the motion to be tested. After this, you will be asked to perform 3 maximal contractions. To perform the maximal contraction, you will be asked to push down on the footplate as hard as possible like pushing on a gas pedal. You will be given 30 seconds to rest between maximal contra ctions. After the maximal test you will be asked to watch the computer monitor to try maintain a line that moves across the screen at a constant height. Th e height of the line changes depending on how hard you push on the footplate. When you feel comfortable maintaining the line at its height you will then be asked to relax. After you rest and when you are ready to start, the submaximal test will begin. The submaximal test will be done with the footplate moving at three slow speeds. You will be asked to push against the footplate, like pushing on a gas pedal, while the footplate moves. During the testing, your muscle act ivity will be measured usin g EMG. The tester will put electrodes on the surface of your skin over your lower leg muscles. The EMG picks up muscle activity and does not send any electr ical activity into your body. You will not feel any sensation with the use of EMG. You will be asked to train for 2 weeks on the tension regulation procedure the same as was described above except that EMG will not be measured while you train. You will be asked to come in for training sessions 3 times a week, on separate days. You will be remeasured at the end of week each week using the above procedure.

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71 Time required : 45 minutes per session Potential Benefits a nd Anticipated Risks : There are no more than minimal risks associ ated with this stu dy. You should consult with a physician if you are unsure whether you ca n participate in this study. If you are injured during this study as a result of the negligence of the princi pal investigator, the University of Florida, the Board of Regent s of the State of Florida and the State of Florida shall be liable only as provided by law. You may seek appropriate compensation for injury by contacting the Insurance Coordina tor at 316 Stadium, University of Florida, (352) 392-2556. We do not anticipate that you will benefit directly by participating in this experiment. Compensation : You will not receive any compensa tion for completing this study. Confidentiality : Your identity will be kept confidential to the extent provided by law. Your information will be assigned a code number. The list c onnecting your name to this number will be kept in a locked file in my faculty supervisorÂ’s office. 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 in this study is complete ly voluntary. There is no penalty for not participating. Right to withdraw from the study : You have the right to withdraw from this study at any time without consequence. You are free to quit any exercise at any time, especially so as to prevent an injury. Whom to contact if you have questions about the study Gerard D. Rozea, MS, ATC/L, Graduate St udent, Department of Exercise and Sport Science, 100 Florida Gym, 392-0584 x 1402 Current address: Department of Health Science, 115 Himes Ha ll, Lock Haven University, Lock Haven, PA 17745, Phone (570) 893-2294, email: grozea@lhup.edu

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72 Mark Tillman, PhD, Assistant Professor, Depa rtment of Exercise and Sport Science, 100 Florida Gym, Phone 392-9575 x1237, email: mtillman@hhp.ufl.edu Whom to contact about your rights as a research participant in the study : UFIRB Office, Box 112250, University of Fl orida, Gainesville, FL 32611-2250; ph 3920433. 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: _______________

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73 APPENDIX B LOCK HAVEN UNIVERSITY INSTITUTIONAL REVIEW BOARD INFORMED CONSENT Informed Consent Protocol Title : Tension Regulation During a Recipr ocal Concentric and Eccentric Muscle Action. Purpose of the research study : The purpose of this study is to gain an unders tanding of participants Â’ ability to regulate eccentric muscle actions (ECC) to better understand the underlying causes of muscle injuries. What you will be asked to do in this study : You will be asked to perform an exercise th at requires fifteen alternating concentric (muscle shortening contraction) and eccentric (muscle lengthening contractions) muscle actions through ankle movement. This exercise will be performed similar to a seated calf raise on the Kin Com isokine tic dynamometer. The Kin Com isokinetic dynamometer will apply resistance and measure your torque during the calf raise exercise. You will then be asked to perform the calf raise ex ercise at three slow speeds (10, 20, and 30 degrees per second) for one session, in a randomized order using a counterbalanced design. During the exercise, iEMG activity will be recorded. You will repeat this session six more times over the course of two week training sessions. Time Required : 30-45 minutes per session Potential Benefits a nd Anticipated Risks : There are no more than minimal risks involve d with participation in this study. You may experience muscle soreness following the se ssions. If at any time you experience discomfort or pain please inform the investig ator and the session will be terminated. We do not anticipate that you will benefit direct ly by participating in this experiment. Compensation : You will not receive any compensa tion upon completion of the study.

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74 Confidentiality : Your identity will be kept confidential to the extent provided by law. Your information will be assigned a code number. The list c onnecting your name to this number will be kept in a locked file in my faculty supervisorÂ’s office. 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 this study is completely voluntary. There is no penalty for not participating. Right to withdraw from the study : You have the right to withdraw from th e study at any time without consequence. Whom to contact if you have questions about the study : Gerard D Rozea, MS, ATC, Instructor/Assistant Athletic Trainer, Department of Health Science, 115 Himes Hall, 570-893-2294 Whom to contact about your rights as a research participant in the study : Dr. Christine Offutt, Chair, Lock Haven Univ ersity Institutional Review Board for the Protection of Human Su bjects at (570)893-2400. 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:

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75 APPENDIX C DATA COLLECTION FORM Trial : _________________________ Name : _________________________ Subject # : _______________ Date : _______________ Height : ______ ft ______ m Weight : ______ lb ______ kg Gender : _______________ Age : _______________ Order of Events : _____ 10°/sec _____ 20°/sec _____ 30°/sec AROM : DF : 1) _______________ PF : 1) _______________ 2) _______________ 2) _______________ 3) _______________ 3) _______________ Average : _______________ Average : _______________ PROM : DF : 1) _______________ PF : 1) _______________ 2) _______________ 2) _______________ 3) _______________ 3) _______________ Average : _______________ Average : _______________ Knee Angle : _______________ MIVC : 1) _______________ 2) _______________ 40% _______________ 3) _______________ Average : _______________ Passive : _______________ Post Stretch AROM : DF : 1) _______________ PF : 1) _______________ 2) _______________ 2) _______________ 3) _______________ 3) _______________ Average : _______________ Average : _______________ PROM : DF : 1) _______________ PF : 1) _______________ 2) _______________ 2) _______________ 3) _______________ 3) _______________ Average : _______________ Average : _______________

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76 APPENDIX D LIST OF ABBREVIATIONS ABS Absolute error score B Baseline from (Experiment 2) BC Baseline control (Experiment 1) BT Baseline treatment (Experiment 1) CNS Central nervous system CON Concentric CV Coefficient of variation DF Dorsiflexion DRM Decreased dorsiflexion ra nge of motion (Experiment 2) ECC Eccentric EMG Electromyelographic GTO Golgi tendon organ ISOM Isometric LG Lateral gastrocnemius MS Muscle spindle MTJ Musculotendinous junction MVIC Maximal voluntary isometric contraction NMJ Neuromuscular junction PEC Parallel elastic component PF Plantar flexion

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77 P/M Peak:mean PROM Passive range of motion PS Post stretch (Experiment 2) PC Post control (Experiment 1) PT Post training (Experiment 1) RMS Root mean square SEC Series elastic component SOL Soleus SSC Stretch shortening cycle

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78 LIST OF REFERENCES Abbrussese, G., Morena, M., Spadavecchia, L., & Schieppati, M. (1994). Response of arm flexor muscles to magnetic and electr ical brain stimula tion during shortening and lengthening tasks in man. Journal of Physiology . 481 (2), 499 – 507. Acierno, S. P., Baratta, R. V., & Solomonow, M. (2001). A practical guide to electromyography: LSU bioengineering laboratory manual . Baton Rouge, LA: Bioengineering Laboratory Allen, G. M., Gandevia, S. C., & McKenzie, D. K. (1995). Reliability of measurements of muscle strength and voluntary ac tivation using twitch interpolation. Muscle and Nerve . 18, 593 – 600. Arnold, B. L., Perrin, D. H., Kahler, D. M., Gansneder, B. M., & Gieck, J. H. (1997). A trend analysis of the in vivo quadriceps femoris angle-specific torque-velocity relationship. Journal of Orthopedic and Sports Physical Therapy . 25 (5), 316 – 322. Avela, J., Finni, T., Liikavainio, T., Niemel a, E., & Komi, P. V. (2004). Neural and mechanical responses of the triceps surae muscle group after 1 h of repeated fast passive stretches. Journal of Applied Physiology . 96 (6), 2325 – 2332. Best, T. .M. & Garrett, W. E. (1996). Hams tring strains: expediting return to play. Physician and Sports Medicine 24, 37 – 40, 43 – 44. Bigland, B., Lippold, O. C. J. (1954). The re lationship between force, velocity and integrated electrical acti vity in human muscle. Journal of Physiology . 123, 214 – 224. Bilodeau, M., Keen, D. A., Sweeney, P. J., Shields, R. W., & Enoka, R. M. (2000). Strength training can improve steadiness in persons with essential tremor. Muscle and Nerve . 23, 771 – 778. Bishop, M. D., Trimble, M. H., Bauer, J. A., & Kaminski, T. W. (2000). Differential control during maximal concentric and eccen tric loading revealed by characteristics of the electromyogram. Journal of Electromyography and Kinesiology . 10, 399 – 405. Bobbert, M. F., Huijing, P. A., & Van Ingen Sc henau G. J. (1986). A model of the human triceps surae muscle-tendon co mplex applied to jumping. Journal of Biomechanics . 19 (11), 887 – 898.

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80 Garrett, W. E. (1996). Muscle strain injuries. American Journal of Sports Medicine . 24, S2 – S8. Guissard, N., Duchateau, J. ( 2004). Effect of static st retch training on neural and mechanical properties of the hum an plantar-flexor muscles. Muscle and Nerve. 29 (2), 248 – 255. Hakkinen, K., Komi, P. V. (1983). Electrom yographic changes duri ng strength training and detraining. Medicine and Science in Sports and Exercise . 15 (6), 455 – 460. Hall, S.J. (2003). Basic biomechanics . (4th ed.). Columbus, OH. McGraw-Hill Co. Pg. 147. Herzog, W., Schachar, R., Leonard, T. R. (2003). Characterization of the passive component of force enhancement following ac tive stretching of skeletal muscle. The Journal of Ex perimental Biology . 206, 3635 – 3643. Higbie, E. J., Cureton, K. J., Warren, G. L., & Prior, B. M. (1996). Effects of concentric and eccentric training on muscle strength, cr oss-sectional area, and neural activity. Journal of Applied Physiology . 81, 2173 – 2181. Hortobagyi, T., Barrier, J., Braspennincx, J ., Koens, P., Devita, P., Dempsey, L., & Lambert, J. (1996). Greater initial adapta tions to submaximal muscle lengthening than maximal shortening. Journal of Physiology . 81 (4), 1677 – 1682. Hortobagyi, T., Hill, J. P., Houmard, J. A, Fras er, D. D., Lambert, N. J, & Israel, R. G. (1996). Adaptive responses to muscle le ngthening and shortening in humans. Journal of Applied Physiology . 80 (3), 765 – 772. Houk, J., & Henneman, E. (1967a). Feedback control of skeletal muscles. Brain Research . 5, 433 – 451. Houk, J., & Henneman, E. (1967b). Responses of golgi tendon organs to active contractions of the soleus muscle of the cat. Journal of Neurphysiology . 3, 466 – 481. Houk, J. C., Singer J. J., & Henneman, E. ( 1971). Adequate stimulus for tendon organs with observations on mechanics of ankle joint. Journal of Neurophysiology . 6, 1051 – 1065. Howell, J. N., Fuglevand, A. J., Walsh, M. L., & Bigland-Ritchie, B. (1995). Motor unit activity during isometric and concentric-eccen tric contractions of the human first dorsal interosseus muscle. Journal of Neurophysiology . 74 (3), 901 – 904. Irgang, J. J., Whitney, S. L., & Cox, E. D. (1994). Balance and proprioceptive training for rehabilitation of the lower extremity. Journal of Sports Rehabilitation . 3, 68 – 83.

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81 Jarvinen, J., Kaariainen, M ., & Jarvinen, M. (2000). Muscle strain injuries. Current Opinion in Rheumatology 12 (2), 155 – 161. Kokkonen, J., Nelson, A., G., & Cornwell, A. (1 998). Acute muscle stretching inhibits maximal strength perfomance. 69 (4), 411 – 415. Komi, P. V., & Bosco, C. (1978). Utilization of stored elastic en ergy in leg extensor muscles by men and women. Medicine and Science in Sports . 10 (4), 261 – 265. Komi, P. V., & Buskirk, E. R. (1972). Eff ect of eccentric and concentric muscle conditioning on tension and electri cal activity of human muscle. Ergonomics . 15 (4), 417 – 434. Komi, P. V., & Gollhofer, A. (1997). Stretch re flexes can have an important role in force enhancement during ssc exercise. Journal of Applied Biomechanics. 13 (4), 451 – 460. Kreighbaum, E., & Barthels, K. M. (1996). Biomechanics: A qualitative approach for studying human movement . (4th ed.). Needham Heights; MA; Allison and Bacon. Lundberg, A., Malmgren, K., & Schomberg, E. D. (1978). Role of joint afferents in motor control exemplified by effects on re flex pathways from Ib afferents. Journal of Physiology . 284, 327 – 343. Manini, T., Baldwin, S., Van Arnam, T., & Ploutz-Snyder, L. (2004). Isotonic force steadiness of the leg extensors is depende nt on intensity and contraction type in pre-clinically disabled older adults. Medicine and Science in Sports and Exercise . 36 (5), S123. McHugh, M. P., Connolly, D. A. J., Eston, R. G., Kremenic, I. J., Nicholas, S. J., & Gleim, G. W. (1999). The role of passive mu scle stiffness in symptoms of exerciseinduced muscle damage. The American Journal of Sports Medicine . 27 (5), 594 – 599. Milner-Brown, H. S., Stein, R. B., & Lee, R. G. (1975). Synchronization of human motor units: possible roles of exercise and supraspinal reflexes. Electroencephalography and Clinical Neurophysiology . 38, 245 – 254. Nardone, A., & Schieppati, M. (1988). Shift of activity from slow to fast muscle during voluntary lengthening contractions of th e triceps surae muscle in humans. Journal of Physiology . 395, 363 – 381. Norkin, C.C., & White, D.Y. (1995). Measurement of joint motion: a guide to goniometry . (3rd ed.). Philadelphia, PA: F.A. Davis Co. Ogiso, K., McBride, J. M., Finni, T., & Komi , P. V. (2002). Stretch-reflex mechanical response to varying types of pr evious muscle activities. Journal of Electromyography and Kinesiology . 12, 27 – 36.

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82 Perrine, J. J., & Edgerton, V. R. (1978). Muscle force-velocity and power-velocity relationships under is okinetic loading. Medicine and Science in Sports . 10 (3), 159 – 166. Pinniger, G. J., Steele, J. R., Thorsten sson, A., Cresswell, A. G. (2000). Tension regulation during lengthening and shortening actions of the human soleus muscle. European Journal of Applied Physiology . 81, 375 – 383. Prentice, W. E. (1999). Rehabilitation techniques in sports medicine . (3rd ed.). Boston; MA: McGraw-Hill. Pugh, G.M. (2003). A biomechanical compar ison of the front and rear lat pull-down exercise. Master’s Thesis. Univer sity of Florida. Gainsville, FL. Safran, M. R., Garrett, W. E., Seaber, A. V., Glisson, R. R., & Ribbeck, B. M. (1988). The role of warmup in musc ular injury prevention. The American Journal of Sports Medicine . 16 (2), 123 – 128. Saladin, K.S. (2004). Anatomy and physiology: the unity of form and function . (3rd ed.). Boston, MA; McGraw Hill. Sale, D. G. (1988). Neural adaptation to resistance training. Medicine and Science in Sports and Exercise . 20 (5), S135 – S145. Seger, J. Y., & Thorstensson, A. (2005). Eff ects of eccentric versus concentric training on thigh muscle strength and emg. International Journal of Sports Medicine . 26 (1), 45 – 52. Semmler, J. G., Kornatz, K. W., Dinenno, D. V., Zhou, S., & Enoka, R. M. (2002). Motor unit synchronization is enhanced during sl ow lengthening contractions of a hand muscle. Journal of Physiology . 545 (2), 681 – 695. Stevens, J. L., Maluf, K. S., Tracy, B. L., Hunter, S. K., & Enoka, R. M. (2004). Fluctuations in isometric force are asso ciated with motor unit discharge rate variability in older adults. Medicine and Science in Sports and Exercise . 36 (5), S123. Tesch, P. A., Dudley, G. A., Duvoisin, M. R ., Hather, B. M., & Harris, R. T. (1990). Force and emg signal patterns during repeat ed bouts of concentric or eccentric muscle actions. Acta Physiologica Scandinavica . 138, 263 – 271. Thacker, S. B., Gilchrist, J., Stoup,D. F ., & Kimsey, C. D. (2004). The impact of stretching on sports injury risk: a systematic review of the literature. Medicine and Science in Sports and Exercise. 36 (3), 371 – 378. Thorstensson, A., Karlsson, J. H. T., Viitasa lo, P., Luhtanen, & Komi, P. V. (1976). Effect of strength training on em g of human skeletal muscle. Acta Physiologica Scandinavica . 98, 232 – 236.

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84 BIOGRAPHICAL SKETCH Gerard D. Rozea was born on August 5, 1974 to his parents Gerard and Mary Rozea in Patchogue, New York. He has two older sisters, Jennifer and Jill. Gerard lived in Mastic, New York throughout his childhood until he enrolled at East Stroudsburg University (East Stroudsburg, PA) in 1992. During his time at East Stroudsburg Univer sity, Gerard majored in Health and physical education with a concentration in athletic training. Cu riosity about human physiology and biomechanics led Gerard to pursue a masterÂ’s degree in movement studies and exercise science with a biophys ical concentration at East Stroudsburg University. This interest continued to deve lop as Gerard began the pursuit of a doctorate in athletic training/sports medicine at the Un iversity of Florida (G ainesville, FL). His clinical experiences and new academic informa tion formed the basis of his dissertation. Gerard is currently employed as an assistant professor a nd assistant athletic trainer at Lock Haven University (Lock Haven, PA) wh ere he will continue as an educator and clinical practitioner, and will continue to pursue his research interests.