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Anticipatory Effects on Lower Extremity Kinematics and Kinetics during Cutting Movements

Permanent Link: http://ufdc.ufl.edu/UFE0025113/00001

Material Information

Title: Anticipatory Effects on Lower Extremity Kinematics and Kinetics during Cutting Movements
Physical Description: 1 online resource (91 p.)
Language: english
Creator: Mizell, Ryan
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: acl, cutting, unanticipated
Applied Physiology and Kinesiology -- Dissertations, Academic -- UF
Genre: Applied Physiology and Kinesiology thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Although gender differences in ACL injuries are a fertile ground for research, the multitude of previous projects has not led to a decrease in injury rates. Many researchers have investigated anticipated athletic movements, but preplanned movements rarely occur during competition. Therefore, unanticipated movements warrant more investigation. The purpose of this study was to investigate the effects of anticipation on lower extremity kinematics and kinetics during movements that are considered high risk for ACL injury. Fifteen males and fifteen females were recruited from undergraduate classes to perform side cuts and crossover cuts. Approach speeds were required to be within the range of 5.5 to 7 m/s and cutting angles were required to be between 35 degrees and 60 degrees. Sampling rates for the cameras and force plates were set at 240 Hz and 2400 Hz, respectively. Concerning unplanned movement, the hip and knee were abducted during the side cut and adducted during the crossover cut. For the unplanned conditions, the movements were performed using similar frontal plane adduction moments at the hip and knee. When lacking the ability to preplan the maneuvers, a similar movement strategy was used. Thus, participants were unable to accommodate to the unplanned movements. Also, increased hip flexion was revealed during the unanticipated movements. Since participants prepared for the unanticipated movements through lowering the center of mass height, accommodation to unplanned movements seems possible in the sagittal plane. Gender differences occurred at the hip as females used less hip abduction to perform the movements. Less hip abduction for females is closer to the ?position of no return? seen in ACL injuries. Although our results confirmed published gender differences, this may have been due a combination of the difficulty of the tasks and the relatively low skill of the participants. Direction differences occurred as the crossover cut was performed with knee abduction and foot pronation while the opposite was true for the side cut. Furthermore, the crossover cut seemed to be performed by utilizing a preceding side cut. Therefore, the crossover cut seems to be a more dangerous movement. Although accommodation for unplanned movements may occur in the sagittal plane, unanticipated cutting movements are performed differently than anticipated cutting movements. Since anticipation can affect the performance of cutting movements, incorporation of unanticipated maneuvers should be included in training prevention programs. Also, increased development of methods for preventing anticipation is required to more closely simulate competition in the lab setting.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Ryan Mizell.
Thesis: Thesis (M.S.)--University of Florida, 2009.
Local: Adviser: Tillman, Mark D.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0025113:00001

Permanent Link: http://ufdc.ufl.edu/UFE0025113/00001

Material Information

Title: Anticipatory Effects on Lower Extremity Kinematics and Kinetics during Cutting Movements
Physical Description: 1 online resource (91 p.)
Language: english
Creator: Mizell, Ryan
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: acl, cutting, unanticipated
Applied Physiology and Kinesiology -- Dissertations, Academic -- UF
Genre: Applied Physiology and Kinesiology thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Although gender differences in ACL injuries are a fertile ground for research, the multitude of previous projects has not led to a decrease in injury rates. Many researchers have investigated anticipated athletic movements, but preplanned movements rarely occur during competition. Therefore, unanticipated movements warrant more investigation. The purpose of this study was to investigate the effects of anticipation on lower extremity kinematics and kinetics during movements that are considered high risk for ACL injury. Fifteen males and fifteen females were recruited from undergraduate classes to perform side cuts and crossover cuts. Approach speeds were required to be within the range of 5.5 to 7 m/s and cutting angles were required to be between 35 degrees and 60 degrees. Sampling rates for the cameras and force plates were set at 240 Hz and 2400 Hz, respectively. Concerning unplanned movement, the hip and knee were abducted during the side cut and adducted during the crossover cut. For the unplanned conditions, the movements were performed using similar frontal plane adduction moments at the hip and knee. When lacking the ability to preplan the maneuvers, a similar movement strategy was used. Thus, participants were unable to accommodate to the unplanned movements. Also, increased hip flexion was revealed during the unanticipated movements. Since participants prepared for the unanticipated movements through lowering the center of mass height, accommodation to unplanned movements seems possible in the sagittal plane. Gender differences occurred at the hip as females used less hip abduction to perform the movements. Less hip abduction for females is closer to the ?position of no return? seen in ACL injuries. Although our results confirmed published gender differences, this may have been due a combination of the difficulty of the tasks and the relatively low skill of the participants. Direction differences occurred as the crossover cut was performed with knee abduction and foot pronation while the opposite was true for the side cut. Furthermore, the crossover cut seemed to be performed by utilizing a preceding side cut. Therefore, the crossover cut seems to be a more dangerous movement. Although accommodation for unplanned movements may occur in the sagittal plane, unanticipated cutting movements are performed differently than anticipated cutting movements. Since anticipation can affect the performance of cutting movements, incorporation of unanticipated maneuvers should be included in training prevention programs. Also, increased development of methods for preventing anticipation is required to more closely simulate competition in the lab setting.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Ryan Mizell.
Thesis: Thesis (M.S.)--University of Florida, 2009.
Local: Adviser: Tillman, Mark D.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0025113:00001


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1 ANTICIPATORY EFFECTS ON LOWER EXTR EMITY KINEMATICS AND KINETICS DURING CUTTING MOVEMENTS By RYAN ASHLEY MIZELL A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2009

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2 2009 Ryan Ashley Mizell

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3 To everyone who constantly asked me when I would finish my thesis

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4 ACKNOWLEDGMENTS Completion of this project would not have possible without a subs tantial effort from many individuals. First, I would like to thank Dr. Mark Tillman for his advice and support. Although Im sure he tired of read ing my drafts, he always provided many keen insights on how to improve my writing and how to correct my many mistakes whether grammatical, biomechanical, or statistical. Next, I would like to thank Dr. Chris Hass for his input on all topics from biomechanics to statistics. This pr oject would not have been the same without his input and appraisal. Next, I would like to tha nk Dr. Ronald Siders fo r agreeing to be on my committee. His experience and knowledge regardi ng many topics greatly eased the process of completing this project. Also, I would like to th ank my parents for all of the support they have provided in my life. I would not be who I am today without them Also, I would like to thank Dr. Kim Fournier and Dr Joe Nocera for always answering a ny of my questions. Their advice was instrumental in this project, and if I did not follow their s uggestions, I later wished that I had. Finally, I would like to thank all of th e participants who volunteered for my study.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ............................................................................................................... 4 LIST OF TABLES ...........................................................................................................................7 LIST OF FIGURES .........................................................................................................................9 ABSTRACT ...................................................................................................................... .............10 CHAP TER 1 INTRODUCTION .................................................................................................................. 12 2 LITERATURE REVIEW .......................................................................................................14 General Introduction .......................................................................................................... .....14 Anatomy ....................................................................................................................... ..........15 Mechanism of Injury ...............................................................................................................17 Predisposing Factors for Injury ..............................................................................................18 Anatomical Factors ..........................................................................................................19 Environmental Factors ..................................................................................................... 22 Hormonal Factors ............................................................................................................23 Neuromuscular Factors .................................................................................................... 25 3 METHODS ....................................................................................................................... ......38 Participants .................................................................................................................. ...........38 Instrumentation ............................................................................................................... ........38 Procedure ..................................................................................................................... ...........39 Data Analysis ..........................................................................................................................41 Data Reduction .......................................................................................................................41 Statistical Analysis .......................................................................................................... ........42 4 RESULTS ....................................................................................................................... ........43 Participants .................................................................................................................. ...........43 Kinematics .................................................................................................................... ..........44 Sagittal Plane ...................................................................................................................44 Frontal Plane ....................................................................................................................44 Transverse Plane .............................................................................................................. 45 Kinetics ...................................................................................................................... .............45 Sagittal Plane ...................................................................................................................45 Frontal Plane ....................................................................................................................46 Transverse Plane .............................................................................................................. 47

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6 5 DISCUSSION .................................................................................................................... .....53 Participants .................................................................................................................. ...........53 Condition ..................................................................................................................... ...........54 Sagittal ...................................................................................................................... .......54 Frontal ....................................................................................................................... .......55 Transverse .................................................................................................................... ....56 Gender ........................................................................................................................ .............57 Sagittal ...................................................................................................................... .......57 Frontal ....................................................................................................................... .......58 Transverse .................................................................................................................... ....58 Direction ..................................................................................................................... ............59 Sagittal ...................................................................................................................... .......59 Frontal ....................................................................................................................... .......61 Transverse .................................................................................................................... ....61 Limitations ................................................................................................................... ...........62 Conclusion .................................................................................................................... ..........65 APPENDIX A MANOVA TABLES FOR NONS I GNIFICANT RESULTS ................................................68 Kinematics .................................................................................................................... ..........68 Sagittal ...................................................................................................................... .......68 Frontal ....................................................................................................................... .......68 Transverse .................................................................................................................... ....68 Kinetics ...................................................................................................................... .............68 Sagittal ...................................................................................................................... .......68 Frontal ....................................................................................................................... .......69 Transverse .................................................................................................................... ....69 B JOINT ANGLES AND MOMENTS ......................................................................................70 LIST OF REFERENCES ...............................................................................................................74 BIOGRAPHICAL SKETCH .........................................................................................................91

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7 LIST OF TABLES Table page 4-1 The average age, height (m), mass (kg) tim e between the signal and IC, and the percentage of successful trials for males and females [* denotes significant difference at P < .05]. Data are displayed as mean SD. ................................................. 47 4-2 Sagittal plane joint angles (degrees SD) for preplanned (PP) and unanticipated (UN) conditions (* denotes significant difference at P < .05 for IC). ......................................... 48 4-3 Sagittal plane joint angles (d egrees SD) for m ales and females ......................................... 48 4-4 Sagittal plane joint angles (degrees SD) for the s ide cut (L eft) and crossover cut (Right) ....................................................................................................................... .........48 4-5 Frontal plane joint angles (deg rees SD) for males and females (* denotes significant difference at P < .05 for IC, denotes significant difference at P < .05 for PEAK). ........ 49 4-6 Frontal plane joint angles (deg rees SD) for the side cut (Left) and crossover cut (Right) (* denotes significant difference at P < .05 for IC, denotes significant difference at P < .05 for PEAK). ....................................................................................... 49 4-7 Frontal plane joint angles (deg rees SD) for preplanned (PP) and unanticipated (UN)(* denotes significant difference at P < .05 for IC). ............................................................... 49 4-8 Transverse plane joint angles (degrees SD) for the side cut (L eft) and crossover cut (Right) (* denotes signif icant difference at P < .05 for IC, denotes significant difference at P < .05 for PEAK). ....................................................................................... 49 4-9 Transverse plane joint angles (d egrees SD) for m ales and females .................................... 50 4-10 Transverse plane joint angles (degrees SD) for preplanned (PP) and unanticipated (UN) conditions .................................................................................................................50 4-11 Sagittal plane joint mome nts (Nm /(kg*m) SD) for the si de cut (Left) and crossover cut (Right) (* denotes significant differen ce at P < .05 for IC, denotes significant difference at P < .05 for PEAK). ....................................................................................... 50 4-12 Sagittal plane join t mom ents (Nm/(kg*m) SD ) for males and females ............................ 50 4-13 Sagittal plane join t moments (Nm/(kg*m) SD ) for preplanned (PP) and unanticipated (UN) conditions. ..........................................................................................50 4-14 Frontal plane joint mome nts (Nm /(kg*m) SD) for prep lanned (PP) and unanticipated (UN) conditions (* denotes signific ant difference at P < .05 for IC). ...............................51

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8 4-15 Frontal plane joint moment s (Nm /(kg*m) SD) for the si de cut (Left) and crossover cut (Right) (* denotes significant differen ce at P < .05 for IC, denotes significant difference at P < .05 for PEAK). ...................................................................................... 51 4-16 Frontal plane joint moments (Nm/( kg*m ) SD) for males and females. ............................ 51 4-17 Transverse plane moments (Nm/(kg*m) SD) for preplanned (PP) and unanticipated (UN) conditions (* denotes significant difference at P < .05 for IC, denotes significant difference at P < .05 for PEAK). ...................................................................... 52 4-18 Transverse plane joint moments (N m /(kg*m) SD) for males and females. ...................... 52 4-19 Transverse plane joint moments (N m /(kg*m) SD) for preplanned (PP) and unanticipated (UN) conditions. ..........................................................................................52

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9 LIST OF FIGURES Figure page 4-1 The percentage of successful trials for m ale and female participants ....................................48 4-2 Direction x condition interact ion for hip joint m oments at IC ...............................................51 4-3 Direction x condition interact ion for knee joint m oments at IC ............................................. 52 B-1 Joint angles during stance phase for m ales (dotted, blue lin e) and females (solid, orange line) for a) hip sagittal plane b) hip front al plane c) hip tran sverse plane d) knee sagittal plane e) knee frontal plane f) knee tr ansverse plane g) ankle sagittal plane h) ankle frontal plane i) an kle transverse plane ...................................................................... 70 B-2 Joint moments during stance phase for male s (blue line ) and females (orange line) for a) hip sagittal plane b) hip fr ontal plane c) hip transverse plane d) knee sagittal plane e) knee frontal plane f) knee transverse plan e g) ankle sagittal plane h) ankle frontal plane i) ankle transverse plane ........................................................................................... 70 B-3 Joint angles during stance phase for side cu t (dotted, blue line) a nd crossover cut (solid, orange line) for a) hip sagittal plane b) hi p frontal plane c) hip transverse plane d) knee sagittal plane e) kn ee frontal plane f) knee transverse plane g) ankle sagittal plane h) ankle frontal plane i) ankle transverse plane ........................................................72 B-4 Joint moments during stance phase for side cut (dotted, blue li ne) and crossover cut (solid, orange line) for a) hip sagittal plan e b) hip frontal plan e c) hip trans verse plane d) knee sagittal plane e) knee frontal plane f) knee transverse plane g) ankle sagittal plane h) ankle frontal pl ane i) ankle transverse plane ...........................................72

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10 Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science ANTICIPATORY EFFECTS ON LOWER EXTR EMITY KINEMATICS AND KINETICS DURING CUTTING MOVEMENTS By Ryan Ashley Mizell August 2009 Chair: Mark Tillman Major: Applied Physio logy and Kinesiology Although gender differences in ACL injuries are a fertile ground for research, the multitude of previous projects has not led to a decr ease in injury rates. Many researchers have investigated anticipated athle tic movements, but preplanned movements rarely occur during competition. Therefore, unanticipated movement s warrant more investigation. The purpose of this study was to investigate the effects of anticipation on lower extremity kinematics and kinetics during movements that are considered high risk for ACL injury. Fifteen males and fifteen females were recruited fr om undergraduate classes to pe rform side cuts and crossover cuts. Approach speeds were required to be w ithin the range of 5.0 to 7.0 m/s and cutting angles were required to be between 35 degrees and 60 degrees. Sampling rates for the cameras and force plates were set at 2 40 Hz and 2400 Hz, respectively. Concerning unplanned movement, the hip and knee were abducted during the side cu t and adducted during the crossover cut. For the unplanned conditions, the movements were pe rformed using similar frontal plane adduction moments at the hip and knee. When lacking the ability to preplan the maneuvers, a similar movement strategy was used. Thus, participants were unable to accommodate to the unplanned movements. Also, increased hip flexion was revealed during the unanticipated movements. Since participants prepared for the unanticipated movements through lowering the center of mass

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11 height, accommodation to unplanned movements seem s possible in the sagittal plane. Gender differences occurred at the hip as females used less hip abduction to perform the movements. Less hip abduction for females is closer to the position of no return seen in ACL injuries. Although our results confirmed published gender differences, this may have been due a combination of the difficulty of the tasks and the relatively low skill of the participants. Direction differences occurred as the crossover cut was performed with knee abduction and foot pronation while the opposite was true for the side cut. Furthermore, the crossover cut seemed to be performed by utilizing a preceding side cut. Th erefore, the crossover cut seems to be a more dangerous movement. Although accommodation for unplanned movements may occur in the sagittal plane, unanticipated cutting movements are performed differently than anticipated cutting movements. Since anticipation can a ffect the performance of cutting movements, incorporation of unanticipated maneuvers should be included in training prevention programs. Also, increased development of methods for prev enting anticipation is re quired to more closely simulate competition in the lab setting.

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12 CHAPTER 1 INTRODUCTION The anter ior cruciate ligament (ACL) prevents anterior displacement of the tibia relative to the femur and functions in ro tational stability of the knee.1-3 In the United States, ACL ruptures occur approximately 100,000 times each year 4. Although primarily o ccurring in athletic populations, women are four to si x times more likely to suffer an ACL injury than men when playing the same sports.5-8 The passing of Title IX in 1972 le d to a dramatic increase of the participation of females in high school and colleg e sports. Unfortunately, an increased number of ACL injuries accompanied this incr ease of female participation.9-11 The majority of injuries to th e ACL occur during noncontact movements.12, 13 High risk movements for ACL injury constitute one leg landings, rapid stops, and pivoting movements which produce a common position that combines a low knee flexion angle with knee valgus and internal rotation of a planted leg.12, 14 This is classified as the position of no return for an ACL injury.15, 16 In this position, the musc les that normally provide absorption of forces can not function properly due to a mechan ical disadvantage, which leads to a greater predisposition for injury. Due to the prevalence of injury and potentia l long term disabil ity, prevention of ACL injury is a main concern of c linicians and scientists. Theref ore, many potentially predisposing factors for ACL injury have been identified and researched. These factors are classified as anatomical, environmental, hormonal, and neuromuscular.4 Anatomical factors tend to be immutable without surgical inte rvention. Environmenta l factors affect bo th genders and are difficult to separate their specific risk due to their intimate interrelatedness. Hormonal factors represent a potentially rich source of research due to the drastic gender differences in serum concentration levels of specific hormones. Howeve r, results have proven to be inconclusive due

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13 to the conflicting nature of many experiments. Neuromuscular factors consist of altered movement patterns, altered musc le activation patterns, inadeq uate muscle stiffness, and decreased muscle strength. With proper traini ng neuromuscular factors tend to be modifiable.17 Although no single factor represents the solitary cause of the alarming rate of female ACL injuries, focusing on the investigation of neuromuscu lar factors is rational due to their modifiable nature with proper training, Gender differences in kinetics, kinematics, and muscle activati on patterns have been documented during high risk movements.4, 18 Female athletes tend to perform high risk maneuvers with less knee and hip flexion, incr eased knee valgus angles, and ankle eversion.12, 14 However, many of these differences were observed during laborator y studies utilizing preplanned maneuvers. In order to gain an improved understanding of the kinematics and kinetics imposed on the lower extremity duri ng competition, a more realistic comparison is required that employs unanticipated movements. Furthermore, kinetics and kinematics of the knee were predominantly examined during these st udies. Therefore, the purpose of this study is to investigate the influence of gender and a vol untary reaction component on the lower extremity during running, side step cutting, and crossover cutting. Results from this research may be used to improve ACL injury prevention programs in orde r to reduce female injury rates more similar to the level of the injury rates of males.

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14 CHAPTER 2 LITERATURE REVIEW General Introduction Injury to the anterior cruciate ligament (A CL) represents one of the most severely devastating injuries in sports.19 Although occurring infrequently in the general population, one in 3000 individuals sustains an ACL injury per year in the United Stat es with half of ACL injuries suffered by young athletes 15 to 25 years old.5, 6 However, women are four to six times more likely to suffer an ACL injury than men when playing the same sports.7, 8 With the passing of Title IX in 1972, a dramatic increase in ACL injuries followed the increased participation of females in high school and college sports.9, 11, 20 Prevention of ACL injury is a main concern of clinicians and scientists due to the financial cost, prevalence of inju ry, severity, and potential long te rm disability. Each injury can cost between $17,000 to $25,000 for surgery and rehabilitation.17 In the U. S., the annual cost for the treatment of ACL in jury totals over $1.5 billion.4, 11 Of this total, $646 million is for ACL repair in high school and college female athletes.6, 21 In addition, nearly 2/3 of patients who tear their ACL suffer from menisci damage and injury to articular surfaces.22 However, the psychological costs that come from potential long-term disability and significantly greater risk of osteoarthritis are harder to measure monetarily and can be more harmful.23 Due to the severity of the injury and the el usiveness of attenuating injury rates, vast resources have been utilized to investigate a plet hora of research topics influencing ACL injury rates. Upon delving into the complex factors that influence ACL inju ry rates, one quickly recognizes the closely intermingled nature of th e different aspects. Al though this project is primarily focused on neuromuscular factors, th e following literature review explores many pertinent topics to give an overall understandi ng of the published research An integral element

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15 of understanding what movements place the ACL in danger is the interac tion of the muscles, bones, tendons, and ligaments of the knee. These topics are reviewed during the anatomy portion of the review. During normal movement, forces can be absorbed by all of the knee anatomy. However, high risk movements place the ACL under greater forces.24 These movements are noted during the me chanism of injury portion of th is review. Although high risk movements place the ACL under greater forces, anat omical factors can influence knee alignment and may predispose individual to be more susceptib le to suffer an ACL injury. These factors are explored in the anatomical fact ors portion of the review. Also hormone levels influence the ability of the passive components of the joints to absorb forces. The effect of hormone levels on joint laxity is documented in th e hormonal factors secti on. In addition, factors that influence the amount of force absorbed by the body during mo vements are explored in the environmental factors segment. During high risk movements, the alignment of the knee may be placed in a position preventing adequate force absorption by th e muscles. Also, fatigue can influence lower extremity alignment, force production, and fo rce absorption. Therefore, lower extremity alignment and control is important during all leve ls of fatigue. These topics and the impact of prevention programs are explored in the section on neuromuscular factors. Anatomy A prerequisite to understanding the complex interaction of factors influencing ACL tears is knowledge of the anatomical characteristics of the knee and its surrounding musculature. Considered the largest joint in the body, the knee has two articulations: the tibial-femoral joint and the patellofemoral joint. Ligaments, muscles, compressive forces, and joint geometry contribute to the stability of the knee. Theref ore, the knee is susceptible to injury due to dependence on these soft tissues for stability.25 The ACL is an important ligament of the knee that is the primary restraint to anterior translati on of the tibia and the main stabilizer of the knee.2

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16 The ACL absorbs 85% to 90% of anterior displacement forces.1, 2 In addition, the ACL is an important factor in rotational stability of the knee and opposes internal rotation of the tibia.3, 26 Therefore, it is the main stabilizer of the knee during pivotal activiti es and also prevents hyperextension.1, 27 Although the ACL is considered one ligament, Girgis et al.1 noted that it is composed of two bundles: the anteromedial bundl e (AMB), and the posterolate ral (PLB). Others have described the ACL as having an addi tional bundle: the in termediate bundle.3, 28 Originating at the posterior portion of the lateral femoral c ondyle, the ACL inserts to a fossa positioned laterally and anteriorally to the medial tibial spine.29 The relative location of the bundles with respect to each other depends upon the knee flexion angle.30 Also, the ACL is sturdier and broader near the femur.1 Regardless, the bundles cooperate to stabilize the knee during movement, but tension is not distributed uniformly.31 Also, during flexion and extensi on the bundles are not of a uniform length. According to Hollis et al.32, the AMB lengthens and tightens in flexion, while the PLB shortens and becomes relaxed. During extens ion, the PLB becomes taut, while the AMB is slack.3 When the knee is fully extended, the AMB is significantly longer than the PLB at an average of 34 mm and 22.5 mm, respectively.29 According to Amis and Dawkins3, the AMB is the major antagonist to anterior translation during flexion, and the PMB performs the same function during extension. During internal a nd external rotation, the PMB becomes stiff.30 Interestingly, single ligament reconstruction imit ates the anatomy only of the AMB, and may not restore normal resistance to tibial rotation.33 The narrowest portion of the ACL is the midsubstance, which can be 3.5 times smaller than the points of origin and insertion.34 However,

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17 Chhabra et al.30 state the most common rupture of the AMB occurs at the femoral insertion site, but the PMB may rupture at the tibial or fe moral insertion site or midsubstance. Any alteration in a segment of the lower extremity affects the kinetics and kinematics at all joints.35 Therefore, ACL injury rates are infl uenced by movement at the ankle and hip.36, 37 The ankle is composed of two separate hinge joints: the talocrural and the subtalar.38 Plantarflexion and dorsiflexion occu r at the talocrural joint, wh ile pronation and supination occur at the subtalar joint.25, 39 Motion of the foot can influence movement of the knee.40 During stance, ground reaction forces are absorbed by the foot and ankle and transfer loads to the knee.37 Also, tibial internal rotation and f oot eversion are coupled by the ankle.41 In women, knee injuries directly correlate with rear foot pronation.42 Dynamic valgus at the knee, the dangerous position that characterizes ma ny ACL noncontact injuries, is marked by ankle eversion.35 Therefore, ankle eversion and inversion angles are important to identify individuals at an increased risk for ACL injury.35 Mechanism of Injury Injury to the ACL occurs predominantly without contact duri ng single limb support ranging from initial contact to peak knee flexion.36 Noncontact mechanisms are responsible for 70% of ACL injuries.12, 13 Although a consensus exists within the literature about the occurrence of contact or lack of contact during an ACL injury, the definition of a noncontact ACL injury differs among researchers. A noncontact injury occurs when there is an absence of player to player contact. A contact injury occurs when an injury to the ACL is preceded by a direct blow to the knee. However, ACL injuries occur dur ing body to body contact with an opposing player, but the contact did not involve a direct blow to the knee. Hewett et al.10 defined this type of injury to be a noncontact ACL injury with pert urbation. Due to the broad nature of this definition, these injuries are di fficult to classify. However, other players can influence the

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18 movements of an individual during the game a nd in controlled settings without contacting the injured player.42, 43 In general, noncontact injuri es to the ACL entail one of three categories: planting and cutting, straight knee landings, and rapid, one leg stops.12, 21 All of the previous movements produce a common position that oc curs with the knee near full extension during landing, planting, or stopping.12, 14 This position includes a flexed and rotated lower back, adduction and internal rotation of the hip, flexion and valgus positioning at the knee, external tibial rotation, and a planted foot. Also, a loss of control of the opposite foot often occurs. In this position, the muscles that would normally help the athlete rema in erect cannot function properly because they are working at a mechanical disadvantage, whic h leads to a greater predisposition for injury. This is known as the position of no return for an ACL injury.15, 16 This body position has been corroborated using video analysis of the orientation of the body.14, 43 However, these studies have also revealed the difficulty of elucidating an accurate representation of the mechanism. In addition, gender differences ex ist in movement patterns dur ing everyday activities like walking.36 Predisposing Factors for Injury Potentially p redisposing factors for ACL inju ry have been classified as anatomical, environmental, hormonal, and neuromuscular.4 Anatomical factors associated with an increased risk of ACL injury include separate measures of anatomical alignment, ACL size and shape, and body mass index (BMI). Unfortunately, the major ity of these factors are mostly immutable without surgery. Environmental factors comp rise meteorological conditions, shoe-surface interaction, and knee braces. Although environmental factors tend to be modifiable, more research is needed in order to clarify discre pancies. Also, interventions for environmental factors may lower the overall ACL in jury rate without a decrease in the difference in the ratio of

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19 female ACL tears to ACL tears in men. Next hormonal factors include the effects that hormones have on knee laxity, muscle functi on, and strength of tendons and ligaments. Although hormonal factors potentia lly represent a huge forward leap in prevention of ACL injuries, previous research conflicts in linking sp ecific periods of the menstrual cycle to increases in ACL injury. Finally, neuromuscular factor s consist of altered move ment patterns, altered muscle activation patterns, inadequate muscle s tiffness, and decreased muscle strength. With proper training neuromuscular fa ctors tend to be modifiable.17 Although no single factor represents the solitary cause of the alarming rate ACL injuries to women, neuromuscular factors tend to be amendable with proper training. Therefore, the con centration of time and resources towards their investigation seems logical. Anatomical Factors Anatom ical factors associated with ACL inju ry are misalignment of the lower extremity, a narrowed intercondylar notch, physio logical laxity, increased Q a ngle, increased pelvic width, tibial rotation, and BMI. Although anatomical f actors appear to have an impact on ACL injury, anatomical factors characterize th e hardest factors to amend when compared to the other groups. Of the anatomical factors BMI represents the most potential for modifi cation, but the evidence has been conflicting. Some researchers contend th at a high BMI correlates w ith an increased risk of ACL injury.44 However, Ostenberg and Roos45 were unable draw conclusions about the relationship between BMI and ACL injury due to th e small percentage of ACL injuries in their sample. Logically, an increase in body mass increases forces during landing. Q angle, the angle formed between the lines that link the anterior superior iliac spine and the midpoint of the patella and the line connecting the tibial tubercle with the midpoint of the patella, can cause a more valgus knee position. Larger Q angles increase the knee valgus angle and place increased medial stress on the knee from the quadriceps femoris muscle.22, 46 Normal

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20 ranges for Q angles are approximately 8 to 17 during full extension with women consistently having higher Q angles than men.47-51 Female college basketball players had larger Q angles than male college basketball players.52 Shambaugh et al.46 reported that recr eational basketball players who injured their knees had a higher Q angl e than uninjured players. However, Q angle was not a significant predictor of injury during dynamic movement.53 Also, significant correlations do not exist betw een Q angle and peak knee valgus during stance phase.54 Numerous studies have been performed to elucidate a relationship between ACL injury and femoral notch size and shape. The notch width index (NWI) measures the width of the anterior outlet of the notch divi ded by the total notch width at the level of the popliteal groove. Logically, a narrower notch would lead to a smaller ACL unable to tolerate loads as well as a larger one.55 Andersen confirmed that AC L size correlates with the NWI.56 However, results from research investigating a relationship betw een ACL size and injury rates has conflicted.28, 5658 The notch width of a unilateral ACL injured knee was smaller than a sized matched uninjured control group.7 Also, females have a smaller sized ACL when compared to males in general and when matched to males of a similar height.57, 59 However, Fayad et al.60 found no gender differences when adjusted by body height. Also, Anderson et al.56 found no gender differences of the NWI. Other measures that investigate the dimensions of the in tercondylar notch include the notch shape index (NSI) a nd the notch area index (NAI).61 When comparing all three of the intercondylar notch measures, the NSI was the only measure to display significant gender differences with males displaying a larger NSI.61 Although evidence for a causal relationship is lacking for ACL injury and femoral notch dimension, an association may exist. Women tend to have more joint laxity than men.12, 62 However, joint laxity has not been directly correlated with ACL injury. Nicholas63 showed that male football players who were

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21 categorized as having increased looseness were more susceptible to knee ligament rupture. However, a subsequent study di d not support Nicholas results.64 Woodford-Rogers et al.65 showed that ACL injured athletes had a greater knee joint laxity than he althy controls. In a prospective study, knee laxity correlated with ACL injury.66 Also, female athl etes resisted knee rotation less effectively than male athletes.67-69 In a study by Huston and Wojtys70, knee laxity of Division I male and female athletes was compared to the knee laxity of recreational male and female athletes. Although the Division I female athletes showed more knee laxity than their male counterparts, they did not show more knee laxity than the recrea tional male or female athletes.70 Perhaps the decreased laxity was a result of training performed by the female athletes. The passive and active structures that span the knee joint can potentially contribute to the stiffness resisting tibial displacement by increasing joint contact force, decreasing tibiofemoral displacement, and lowering the force sustained by the ACL.6, 69 Also, Chandrashekar et al.71 reported a striking development by indicating that the structural qualities of the female ACL are not only based on size but can be attributed to ge nder differences in resisting mechanical stress and strain. Frequently linked to knee injury, excessive subtalar pronation may be a factor in ACL injury.72 During ground based movement, the foot a nd the lower leg shift in relation to each other. During pronation of the foot, an internal rotation of the tibia takes place.40 As a restraint to rotation, this position may place the ACL in a hazardous position. Navicular drop, the distance traveled by the navicular tuberosity upon transitioning from seated to standing, has been employed as a gauge for foot pronation.73, 74 Also, navicular drop may be used to predict anterior translation of the tibia.75 Excessive navicular drop has been documented in ACL injured athletes when compared to uninjured participants.65, 74 However, an association between excessive

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22 navicular drop in ACL injured athletes of both genders was not found when compared to uninjured athletes.76 Environmental Factors Environm ental factors include playing surf ace type, meteorological conditions, footwear type, and ground hardness. Outdoor sports produce a greater number of injuries during the dry part of the season when the ground su rface is warmer, drier, and harder.77, 78 Increase in water evaporation and decreases in ra in fall produce such a setting.79 The impact of drier conditions on injury rates has been corroborated in many spor ts and countries. In Holland, children suffered from increased and more severe injuries in spring than in the winter.80 Over the last decade in Australia, warmer climate teams have had a greater injury incidence than the teams based in a colder climate.78 In addition, a dry season bias was s hown for increased ACL injury rates in open stadiums with AstroTurf, but not in closed stadiums containing AstroTurf.78 Other factors that influence the coefficient of friction are cleat number and location and type of playing surface. Longer cleats on the peri pheral of the shoe sole with shorter spikes on the interior were worn during more ACL injuries in a three year span than three other cleat types. The more dangerous cleat design produced grea ter traction on artificial and natural turf.81 In regards to playing surface, th ere was no statistically significan t difference between the overall incidence rate of ACL injury and surface type when comparing natural grass to turf.78, 82-84 However, an increased risk of injury exists when comparing artificial indoor floors to wooden floors.14 Although the previous studies pr ovided solid evidence for envi ronmental factors having an effect on ACL injury, there are some potential li mitations. Due to environmental factors being so closely related, there is a possibility of c onfounding errors between kno wn factors in addition to previously unforeseen factors. The connection among ground hardness, shoe-surface

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23 interaction, and meteorological conditions may cau se difficulty when trying to distinguish among them.85 In addition, the firmness of playing surf ace can be inconsistent throughout the season due to disparate levels of rainfall.78 Also, previous researcher s have not investigated the variability through the season of s hoe and spike selection, overall game speed, or the influence of player position on injury rates. Although environmental factors tend to be modifiab le to an extent, more research is needed in order to clarify some disc repancies. However, Orchard78 asserts an important appraisal of altering environmental conditions. Athletes may re sist a manipulation of environmental factors for preventative reasons because a decrease in spor ts performance may result. Athletes and fans may not be willing to decrease the injury rate due to a possible decrease in performance. Although an intervention that po tentially decreases the risk of injury at the detriment of performance may not be practical for professiona l sports, such an intervention could be a boon for amateur and recreational sports because it is so easily modifiable. However, Girard et al.86 showed a decrease in friction between shoe and surface will reduce acu te injuries, but will produce greater muscle strains/spas ms. More research is needed to investigate the precise coefficient of friction for each sport and, if possible, each individual. Further confounding the problem of environmenta l factors is the influence of competition level on injury rates. Overall injury rate s are increased during competition compared to practice.87, 88 Similarly, ACL injuries occurred mo re often in handball games compared to handball practices.89 An increase of injuries during competition when compared to practice could be explained by a greater motivation and desire to succeed during competitions. Hormonal Factors Com prised of three divisions, the standard me nstrual cycle lasts 28 days. During days 1-9, follicular phase comprises the first day of menses until ovulation.11 Marked by low

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24 concentrations of progesterone and estrogen, an increase in estrogen a nd leutinizing hormone brings about the ovulatory phase.90 This phase is usually arou nd 10-14 days past menses during which estrogen reaches peak secretion. During the luteal phase, comprising days 15-28, progesterone reaches peak concentration.91 Also, relaxin levels rise during the follicular and luteal phases.92 In addition, testosterone levels fluctuate with the menstrual cycle.93 The hormones of the menstrual cycle are capable of affecting many facet s of performance. Ovarian hormones such as estrogen, progesterone, a nd relaxin modify joint laxity and affect the neuromuscular system.94-96 According to Sarwar et al.97, estrogen levels significantly affect muscle function, tendon, and ligament st rength. In addition, decreases in VO2max and motor skills have been found during the luteal phase.98, 99 Slauterbeck et al.100 showed that the tensile properties of rabbit ACL were reduced when estr ogen was introduced. However, the reliability of studies involving animals that are not prim ates is questionable due to not undergoing a menstrual cycle.101 Furthermore, receptor sites for estrogen and progesterone are present on human ACL.102, 103 This finding lends support to the suppos ition that tensile properties of the ACL are influenced by female sex hormones. Due to the preceding potential harmful effect s, the link between hormonal fluctuations and ACL injury during the menstrual cycle represents a rich source of interest for research. Due to fluctuations in serum concentrations of fe male sex hormones, researchers have hypothesized that a specific phase of the menstrual cycle would coincide with an increased risk of injury in female athletes. Although plausi ble that the risk of an ACL in jury occurring varies throughout the cycle, evidence has been conflicting. The follic ular phase was reported to be the phase when female athletes were most at risk of suffering an ACL tear.7, 100 Also, the ovulatory phase was

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25 reported to have an increased risk of injury.104-106 Conversely, evidence for the ovulatory phase having fewer injuries has been published.7, 89 Previous research had some limitations. First, some studies relied on self-reported questionnaires to determine the ph ase of the menstrual cycle of the participants. The reliability of questionnaires is uncertain at best. Questionnaires were reported to be unreliable when compared to urine assays.105 Also, the validity of serum or saliva tes ting is controversial.100, 107 Second, pinpointing the exact date of laxity due to oscillating hor mone levels is difficult due to the possibility of measurable changes in joint laxity arising several days after changes in hormone levels.93 Next, many studies are based on the cy cle lasting the standard 28 days, but cycles can last from 25 to 35 days.108 Finally, some of the participants were taking oral contraceptives. This would give a much differe nt hormone profile than participants who were not ingesting oral contraceptives.90 Furthermore, athletes who are taking oral contraceptives have a lower overall injury rate a nd a decreased risk of ACL injury.105, 109 Neuromuscular Factors Representin g the most modifiable of the f actors influencing ACL injury, neuromuscular factors include altered movement and recruitm ent patterns employed during activity. For the majority of neuromuscular factors, improvement to a more secure pattern of movement seems plausible. However, many studies performed to elucidate differences in movement and recruitment patterns have occurred in a c ontrolled laboratory sett ing. Although controlled laboratory research is necessary to further advance the knowledge base of the prevention of ACL injuries, the limitations inherent to this form of research prevent our understanding of the role of interaction that different factors play by treating each factor as a discrete entity. Although the continued accumulation of advanced research furt her aids in clarifying the association between neuromuscular factors and injury rates, furt her research encompassing a more holistic and

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26 prospective nature should be undertaken. Furt hermore, these factors exist on a continuum and vary between genders and within each gender. Th erefore, researchers should not assume that the average movement strategy for males is a succes sful strategy for avoiding ACL injury. How complex factor interactions affect at risk indivi duals of both genders must be better understood if the risk of ACL injury is ever to decrease. Several potentially dangerous movement im balances such as leg dominance, ligament dominance, and quadriceps dominance are freque ntly observed in female athletes. These imbalances may lead to a decreased neuromuscula r control of the joint and stress the passive ligament structures, exceeding the failure strength of the ligament. Leg dominance is classified by significant strength and flexib ility differences between legs. Potentially dangerous to both legs, the nondominant leg is unable to absorb potentially hazardous fo rces to the knee. Furthermore, a greater dependence on the dominan t leg to absorb the fo rces of movement may produce excessive damage. Female athletes have significant differences in contralateral leg strength and flexibility.110, 111 Athletes with significant strength and flexibility imbalances between legs incurred higher injury rates.112 In a prospective study, athletes who suffered an ACL injury had a dominant knee abduction mo ment 6.4 times greater than the nondominant leg.21 Quadriceps dominance is exemplified by an imbalance between the quadriceps and hamstring strength, recruitment, and coordination. The hamstrings, an ACL agonist, are most influential at 15 and 30 of knee flexion.113 The quadriceps, an ACL antagonist, is capable of loading the ACL throughout th e entire range of motion.114 However, quadriceps activity decreases with increased hip flex ion. Others have re ported that the highest strain of the ACL produced by quadriceps contraction occurs at 15 of knee flexion.113, 115 Also, the hamstring is

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27 unable to aid the ACL in preventi ng anterior translation of the tibia at low knee flexion angles.116 Females recruit their hamstrings less effectiv ely at knee flexion angles between 15 and 25 when compared to males.117 This supports the as sertion that noncontact AC L injuries are likely to occur with the knee near full extension. Contraction of the quadriceps w ithout cocontraction of the hamstrings can lead to greater loads on the ACL. An eccentric quadriceps c ontraction can generate up to 6000 newtons (N).118 This far exceeds the tensile strength of the ACL at 2100 N.119 When these forces are coupled with tibial rotation, an impingement of th e ACL in the femoral notch could result.120 Other factors also contribute to an incr eased rate of injury of women. Female athletes are predisposed to an increased extensor moment about the knee.70 Hewett et al.110 reported a peak knee flexion moment that was three times greater in male athletes compared to females. During running and cutting movements, women tend to recruit the qu adriceps more and the hamstrings less while utilizing a decreased knee flexion.121, 122 Also, the ratio of the streng th of flexion to the strength of extension (H/Q ratio) has been found to influence injury rates. Women have less quadriceps and hamstring strength afte r normalizing for body weight.123, 124 Also, co-contraction of the muscles surrounding the knee was more effective in protecting the ligaments in males than in females.125 Recently, the gastrocnemius has been recogniz ed as an antagonist to the ACL. The gastrocnemius is capable of loading the ACL at decreased knee flexion angles. Fleming et al.126 documented a significantly increased loading of the ACL by the gastrocnemius at knee flexion angles of 5 and 15 when compared to knee flexion angles of 30 and 45. OConnor127 postulated that a cocontraction of the quadri ceps and gastrocnemius produces an increased loading of the ACL during movements performed utilizing low knee flexion angles. This was

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28 confirmed by Fleming et al.,126 who reported that a cocontract ion of the gastrocnemius and quadriceps produced more loading on the ACL th an the addition of sepa rate contractions. Similar to quadriceps loading, the hamstring proved an adequate agonist to gastrocnemius loading of the ACL at knee flexion angles of 30 and 45.126 As was stated previously, most injuries to the ACL fall under one of three categories: pivoting, landings with an erect posture, and ra pid decelerations. During landing from a jump, ground reaction forces (GRF) can be three to 14 times body weight.128 Minimizing GRF is vital to ACL injury prevention due to ACL strain peaking at the maximum GRF.129 Increased GRF correlated with an increased anterior shear force and greater knee abduction torques.21, 130 During a jump landing, decreased de grees of knee flexion angle are associated with increased GRF. Therefore, decreasing landing GRF would translate to a decrease in forces at the joints of the lower extremity. A plethora of research documenting gender di fferences during jump landings exists. Women tend to land with a greater extension of the knee and hip when compared to men.49, 131, 132 In addition, female athletes display an increased valgus angle at ground contact when compared to men. 111, 123, 133, 134 Athletes with high valgus moments at the kne e have been referred to as being ligament dominant.135 During high risk movements, the forces of movement represent greater loads than the musculature of the athlete can safely absor b. Therefore, the knee ligaments are utilized to absorb landing forces rather th an the surrounding musculature. Th is tends to increase valgus knee moment and GRF through an increase of medial knee motion.111 According to Dugan,136 ligament dominance is characterized by the inabili ty of the leg musculature to control motion results in high strains across the ACL as it acts to limit valgus force. This can lead to the previously mentioned position of no return. Fe male athletes tend to suffer from this imbalance

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29 at a greater rate than their male counterparts.110, 111, 137 This is important be cause a valgus load of 5 on the ACL can produce up to 6 times the force of the knee in normal alignment.138 Furthermore, an increased knee valgus can predic t individuals who are more susceptible to ACL injury.21 However, Fagenbaum et al.139 reported that women landed with 10 to 14 greater knee flexion than men. However, the authors stat ed this could be from the small sample being comprised of varsity basketball players who were instructed in correct landing technique. Urabe et al.117 reported no significant differe nces in knee flexion angle between genders during a one leg landing from a maximum vertical jump, but did find that female athletes recruited their quadriceps more than male athletes. This can lead to a greater net extensor torque at the knee. Presently, investigations of th e effect of ankle kinetics and kinematics on ACL injury rates are becoming more prevalent. However, results conflict due to differences in the investigated task. During a jump stop and cut movement, fe males displayed a greate r amount of peak ankle eversion.35, 140 Also, females have produced a greater range of movement at the ankle, which may act as a different program for force absorption.35, 141 During jump landings, females have shown greater peak dorsiflexion, peak pronation, and greater planta rflexion at initial contact.133, 142 During side step cutting, females showed in creased peak pronation angles at the ankle and more inversion throughout stance.42, 143 Results from other studies have produced no differences at the ankle between genders.132, 144 Similarly, movement at the hip influences control of the knee.145, 146 Hip adduction positively correlated with knee abduction angles in women, which places the athlete in a potentially dangerous position for ACL injuries.21 During drop landings, females landed with a decreased peak hip flexion angle.132 This places females in a more erect posture during landing that can place more stress on the ACL as the hamstrings are unable to more effectively prevent

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30 loading. Conversely, similarities to males have also been documented as no differences in peak hip flexion angle, peak hip extension moments, or EMG ac tivation levels were produced.133, 147 Although results may have been affected by the training level of each sample, the previously reported differences occurred during studies using samples composed of Division I athletes. Other athletic movements implicated for produc ing high risk motions include running, side cutting, and crossover cutting. During running, fema le recreational athletes had greater internal rotation and greater adduction of the hip when compared to male recreational athletes.148, 149 During a cutting maneuver, female recreational athletes produced decreased hip flexion and increased hip adduction when compared to male recreational athletes.42 Similarly, Division I soccer athletes produced greater internal rotation angles and decreased flexion angles at the hip and increased adduction moment, decreased extens ion moment and internal rotation moment at the hip.145, 150 Displaying such potentially dangerous positions is troubling due to these movements occurring in experienced athletes Conversely, a random cutting trial displayed a decrease in peak hip adduction compared to th eir male counterparts during early stance phase.151 Although there was no anticipated condition upon whic h to compare these results, the results are surprising due to the unanticip ated movement more closely resembling the conditions of competition. Maturation influences overall injury rates in females.152 Preceding puberty, boys and girls have similar neuromuscular characteristics as both genders perform landing in a safe manner.153 However, maturation results in a divergence of performance between the genders differently. In boys maturation produces increases in strength a nd vertical jump height but females lacked similar performance increases.153-155 Similarly, the maturation of boys produced a valgus motion at the knee during a jump landing, but with matu ration females displayed knee valgus during a

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31 jump landing.130 Similarly, prepubescent females landed with an increased knee flexion from a drop jump when compared to female adults.156 Hewett et al.153 postulates that the maturation of girls is not accompanied by a neuromuscular spurt which has been documented during the maturation of boys. Due to lacking this spurt, ne uromuscular training represents a vital role in the injury prevention plan for females. Neuromuscular training is a promising endeavor that has displayed a great potential to decrease the risk of ACL injury due to the possible modification of neur omuscular control during high risk athletic maneuvers. Of the publishe d studies, the effectiven ess of the prevention program is assessed through monitoring injury ra tes for a specific amount of time or through changing biomechanical measurements. Therefor e, changes in many neuromuscular measures and decreased injury rates have been documen ted utilizing protocols of varying forms and durations. Focus on improvement of movement w ith a more neutral lower extremity alignment and softer landings are the cornerstones of ma ny successful programs. Other components of successful programs include stretching, resistan ce training, and plyometrics. Studies that included stretching, strengthening, plyometrics and agility trai ning were consistently able to decrease injuries in the intervention groups.124, 157, 158 Also, decreases in knee varus and valgus, increasing the H/Q ratio, increase d hip abduction, and decreased hip internal rotation were also produced.110, 159, 160 A six week intervention of strength training involving medicine balls and core strengthening with college athletes decreased peak knee flexion angle and at initial contact during a drop jump.161 Interestingly, this protocol showed a trend towards increasing knee valgus and internal rotation at initial contact. Although not statistically significant, this development is troubling as valgus and internal rotation of the knee being motions the program was attempting to decrease. An intervention prog ram using weight traini ng and balance training

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32 on a BOSU ball decreased peak knee frontal angles during the performance of a high risk maneuver.162 Although few examples of ineffective trai ning programs exist, some protocols were unable to decrease injury rates or improve biomechanical variables. Herman et al.163 utilized elastic band training during single jo int movements and did not alter the kinetics of an athletic movement. The protocol may have proven ineff ective due to a lack of carryover from training single joint open kinetic chain movements to a multiple joint close kinetic chain movement. Wobble board and balance mat training did not elic it significant changes in hip and knee angles during cutting and landing movements.164 Similarly, wobble board training and landing technique training did not decrease injuries.62, 165 However, one study incurred a 37% decrease in sample size due to decreased participation.62 Heidt et al.166 utilized a customized exercise protocol that did not decrease ACL injuries. However, the specific protocol used in the intervention program was not documented in the article.166 Although results look promising, there have been several limitations. When a specific category of training such as balance or core training was unable to produce a decrease in ACL injury or a measurable alteration in biomechanical variables, the entire category of training need not be discounted. The reason for unsatisfact ory results more likely originates with the researchers specific application of training within the category. Therefore, the entire training category does not warrant a dismissal. Simila rly, the mode of training was provided without specifics details. Since each category of training contains multiple facets, more descriptive measures of each category are needed to advan ce thinking and research. For example, weight training was included in many st udies. Yet, lifting with a low intensity and high volume provides vastly different adaptations than lifting with a high intensity at a low volume.

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33 Furthermore, many studies applied a diverse tr aining protocol compos ed of many methods. Though a variety of methods intuitively seems the best option for a prevention program, training diversity provides confounding factors due to being unable to separate spec ific causes and effects of a certain modality. On the ot her hand, the reason that training results have been positive may be due to the decreased baseline of conditioning seen in female athletes.167 Due to such a low level of preparation, any interv ention would produce positive results Also, a limiting factor of some prospective studies is the sample size.124, 158, 168 Although significan t differences were found between the interventi on and control groups, no noncontact ACL injuries were documented in one study.124 Therefore, sample sizes in futu re studies should be increased to gain a more accurate assessment. In additi on, the measurement upon which prospective studies are based is athlete exposures. However, variations exist in meas uring exposures as some factor in the number of hours of participation and others count each practice or game as one exposure regardless of time engaging in actu al participation. Th erefore, study comparisons are difficult to make. Fatigue, a reduction in performance due to ex ercise, may adversely modify neuromuscular control of the lower extremity and decrease th e ability of soft tissue to stabilize joints.169 Evidence of fatigue affecting the bodys ability to control movement is produced by injuries occurring more frequently during latter stages of periods during games and more frequently in the second half compared to the first half.87 Fatigue stems from multiple sources and can be characterized as peripheral fatigue or central fatigue.169 Peripheral fatigue occu rs at or distal to the neuromuscular junction or sarcolemma. Al so, peripheral fatigue may be characterized by occurring during electrochemical coupling, crossbridge release during ATP hydrolysis, or from lacking nutrients. Central fatigue occurs when the body is unable to voluntarily activate motor

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34 neurons.169 Previously, many local fatigue models involving mainly one muscle group were employed.170-173 However, more general fatigue models have been employed in order to more closely simulate realistic spor ts situations through the producti on of fatigue at the local and central level.174 Therefore, contrasting results from studies may be attributable to dissimilar fatigue protocols and analys is of different movements.175, 176 Local and general fatigue protocol s differ with the type of fati gue elicited. Local programs produce peripheral fatigue and general protoc ols produce peripheral and central fatigue.169 The use of local fatigue protocols have been shown to demonstrate a decrease in proprioception of the knee, delayed muscle response, and decrease d isokinetic torque of the knee flexors, and decrease in the ability of the muscle to absorb energy.170-173 General fatigue programs have been shown to decrease peak isokinetic strength of the knee extensors and flexors, decrease the ability of the muscle to absorb energy, and decrease mental performance.173, 177, 178 The influence of general fatigue on high risk movements such as landing and cutting have been investigated. Fatigue influences the lower extremity duri ng high risk movements through increasing hip internal rotation, decreasing hip flexion angles, increased knee abduction and internal rotation, and increased external rotation of the ankle.176, 179, 180 Conversely, fatigue did not influence knee varus/valgus angles in men or women.179 Also, a lack of eccentric control of the hip and knee was noticed. Eccentric control is very important during sudden direction changes to insure safety during movements.171 Gender differences exist in the techniques used to plant and change direction. A side cut involves planting the foot opposit e the direction of movement, while a crossover cut involves planting the foot on the same side of the new direction of movement.181 These dangerous movements double knee valgus mome nts when compared to running.24 Female athletes perform

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35 cutting maneuvers with a decreased knee flex ion angle which may prevent the agonistic hamstrings from protecting the ACL.42, 121, 182 Also, women tend to increase knee valgus angles during a cutting maneuver.35, 42, 121, 183 However, the tasks performed during the previous studies were preplanned and may not accurately represen t measurement of the kinetics and kinematics utilized during competition.184 During competition, cutting maneuvers are not preplanned and can be performed at 5.0 to 7.0 meters per second.185 Recognizing the limitations of extrapolating results from anticipated movements during controlled laboratory studies to co mpetition situations, researchers have identified the need for gender comparisons during experiments that more closely simulate game conditions. McLean et al.42 compared side cutting with and without a defensive opponent. The addition of a defensive opponent caused females to utilize a more erect posture, a greater knee valgus, and increased foot pronation. Under unanticip ated conditions, Ford et al.111 reported that females had greater knee abduction at initial contac t and greater ankle eversion a nd inversion during a cutting maneuver. Under similar conditions, Pollard et al.151 reported significant gender differences in peak hip abduction over the first 40 of knee flexion during unanticipated cutting maneuvers. However, no gender differences in kinetics or kinematics of the knee were reported. Also, the two previous studies lacked a preplanned conditi on to compare with the unanticipated data and did not investigate the entire lower extremity. While research is available that has focuse d upon gender differences during unanticipated movements, few groups have simultaneously investigated the influence of gender under anticipated and unanticipat ed conditions on loading of the entire lower extremity. Besier et al.184 investigated loading at the knee under preplanned (PP) and unan ticipated (UN) conditions. The researchers reported external fl exion/extension moments at the knee joint were similar between

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36 PP and UN conditions. Howeve r, movements performed dur ing UN conditions can double varus/valgus moments a nd internal/external rota tion moments at the knee 184. Although these results are compelling, the sample of the previous study consisted only of males. Houck et al.186 showed UN movements decreased hip abduction a ngles when compared to PP movements. However, the average speed of all tasks was 2.0 m/s. During competitions, an individuals speed before performing a side cut maneuver can be between 5.5 and 6.5 meters per second.185 Extrapolating the results from this study to athle tic movements in situations similar to games or practice is problematic at best. Furthermore, gender comparisons were not made. Sell et al.187 compared PP and UN jump tasks to investigate how gender influences knee loading. Direction and reactivity can affect loading at the knee. However, a task that consisted of a low risk hop and cut was utilized. Also, data of the entire lower extremity were not provided, as only the kinetics and kinematics of the knee were reported. Finally, Borotikar et al.174 investigated how fatigue and reaction influence lower extremity alignment during a high risk landing and response maneuver. The lack of planning prior to the una nticipated movements affected hip extension and internal rotation at initial contact and peak knee and ankle angles However, gender comparisons were not made due to a sample composed of only females. Furthermore, kinetic data were not reported. Also, the examined task utilized a hor izontal jump prior to th e reactive movements. Although a high risk movement, the i nvestigation of other tasks is important to provide a broader base of knowledge to discern the intera ction of neuromuscular factors. As was previously mentioned, noncontact ACL injury mainly occurs under three conditions: planting and cutting, land ing with a more erect posture, and unilateral decelerations. The purpose of this study is to investigate the e ffects of gender on kinetic s and kinematics of the entire lower extremity during anticipated and unanticipated planting and cutting maneuvers and

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37 relate these findings to the poten tial for ACL injury. Due to the plethora of previous studies utilizing anticipated movements, a comparison un der both conditions would provide a link in the literature to better interpret movements performe d under anticipated conditions and generate an improved understanding of lower extremity move ment during conditions more specific to competition. The results from this study may help clarify gender differences in the response to unanticipated movements and improve future trai ning methods for female athletes. Currently, most research implemented for neuromuscular tr aining focuses on the improvement of technique from jump landings.78, 188 However, ACL injuries occu rring during planting and cutting constitute a larger percentage of the total noncontact injuries.189, 190 Therefore, results from this study may be utilized to improve training progr ams that focus on technique improvements of a cutting maneuver 35. Incorporation of the results fr om this study may improve prevention programs to aid in decreasing injury rates in males and females. We hypothesized that females would perfor m the cutting maneuvers under anticipated conditions displaying kinematics and kinetics more closely resembling the common mechanism of ACL injury such as a more erect posture at the knee and hip, internal rotation of the knee and hip, hip adduction, knee abduction, and ankle ev ersion. Also, it is hyp othesized that the unanticipated condition will exacerba te the alignment of the lower ex tremity in both genders to a more dangerous position compared to the anticipa ted condition. However, it is hypothesized that the unanticipated condition will have a more poten tially deleterious effect on the lower extremity kinematics and kinetics of females with respect to ACL injury than males.

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38 CHAPTER 3 METHODS Participants Thirty healthy college-aged m ale and female indi viduals were recruited to participate in the study. Eligible individuals did not have any previous or existing injury to the lower extremity that required surgery. Before participating in the experiment individuals were informed regarding the experimental prot ocol and read and signed an informed consent agreement under the established guidelines of the Institutional Review Board (IRB) of the University of Florida. Testing involved one sess ion for each participant. Instrumentation Three-dim ensional motion analysis was perfor med using a Vicon MX system. The motion analysis system consisted of ten digital cameras (8 MX20 cameras and 2 MXF20 cameras, Oxford Metrics Ltd., Oxford, England) collected at 240 Hz. In addition, a Bertec force platform (Type 4060-10, Bertec Corporation, Columbus, OH) sampled at 2400 Hz was used to collect ground reaction force (GRF) data. To provide a di gital video image of the participant, a Basler camera (A602FC Basler, Inc., Exton, PA) was located lateral to the force pl ate. A light signal system was created to signal the direction of the maneuver. The system consisted of a horizontal line of three light bulbs on a board connected to a switch box with one switch per each light, and was connected to the Vicon System to provide an analog signal to determine the elapsed time between the stimulus for the direction of movement and contact of the foot with the force plate. Nexus Software (Version 1.2) was used to obtain a ll kinetic and kinematic data. Also, Speedtrap 2 electrical timing gates (Brower Timing System s, 2004, Draper, Utah) were employed to ensure the correct speed was maintained throughout all trials. Excel 2003 (Microsoft Corporation, Redmond, Washington) was used for data reducti on. Statistical analyses of the loading on the

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39 lower extremity and GRF was performed using SPSS 2008 (SPSS Incorporated, 2008, Chicago, Illinois). Procedure All data collection s occurred in the Biomechanics Lab at the University of Florida. Prior to the participants arrival, calibration of the Vicon MX sy stem occurred with acceptable calibration error rates less than .25 mm. Also, th e force plates were calibrated to zero. Upon entering the laboratory, participants were provided an Informed Consent form to read and sign. After completion of the Informed Consent, the participants we re asked with which leg they would prefer to kick a soccer ball. In order to guarantee correct performance of the movements, each maneuver and condition was described and demonstrated by the primary investigator. Prior to performing the movements, anthropometric measurements were collected. Measurements included height, weight, bilateral knee and ankle widths, a nd bilateral length of the combined thigh and leg segments. Reflec tive markers were placed on the following lower extremity landmarks (left and right): posterior superior iliac spine, anterior superior iliac spine, thigh, lateral knee, shank, lateral malleolus, calcaneus, and 2nd metatarsal. Each participant wore shorts that did not cover the markers, a tight fitting shirt, and their own shoes. After application of the markers, a static trial wa s collected before any dynamic trials. Static trials involved the participant standing motionless on the force plate, allowing calculation of intermarker distances to be applied during dynamic movement. Each maneuver was preceded by a run at a speed between 5.0 to 7.0 meters per second (m/s).191 In order to ensure that speeds were ma intained throughout each trial, electrical timing gates were placed at 0.1 m and 1.1 m before the for ce plate. In order to decrease the possibility of targeting, each participant was required to find a starting point that placed his or her right foot near the middle of the force plate during a natu ral stride. Participants were allowed as many

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40 trials as needed to locate their starting mark. Upon finding the starting point, participants were instructed to start at the mark and maintain the same speed for each trial. The runway length was 8 m. Using their right foot to plant, the tasks pe rformed by the participants were as follows: a cut to the left at an angle between 35 to 60, continue to run stra ight, and a crossover step at 35 to 60 to the right.160, 191 The tasks were performed unde r two conditions: anticipated and unanticipated. In order to differe ntiate between the categories, a light signal system was used. Prior to performing the anticipat ed condition, the participant wa s informed verbally by the primary investigator which movement to perform. During the run prior to the performance of the maneuver, the primary investigator pressed a switch to illuminate th e corresponding light. The timing of the signal was calibrated to each participant.184 To decrease variability, the primary investigator determined the time to press the switch for each participant. To gauge the location of the participant, the primary investigator employed a live feed from a video camera connected to a separate computer. The digi tal camera was positioned on the wall 1.88 meters above the floor and orthogonal to th e direction of movement. For the first attempt at calibration, the stimulus was displayed when the participan t wass approximately 0.61 m prior to contact with the force plate. After each uns uccessful calibration, the distance from the force plate at which the stimulus was provided increased by approxi mately .305 m. Calibration ceased when the participant was able to consistent ly perform the correct movement. For a trial to be analyzed, participants were re quired to approach the force plate at a speed between 5.0 to 7.0 m/s, cut at an angle of 35 to 60 using their right foot to plant, and perform the correct movement.191 Infrared timing gates were used to ensure the speed was comparable among participants. Orange cones beginning at the center of the force plate and placed at the

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41 angles of 35 to 60 was placed on the floor to monitor the correct angle of movement during the side cut and crossover cut.54 To decrease the effects of fatig ue, participants were allowed as much time as needed between trials. Each move ment was performed five times for a total of 30 trials. The order of the 30 trials was comp letely randomized prior to the arrival of the participant. Following the randomization, each tria l order for the female participants was paired with a male participant. Data Analysis Vicon Nexus software provided all calcula tions of lower extremity joint kinetics and kinematics. Coordinate data wa s filtered with a Woltering spline fi lter using a mean square error of 20 mm.150 All kinetic data was calc ulated using standard inve rse dynamic equations, and all results were normalized to body mass (Nm/kg). Vertical GRF surpassing and decreasing below 10 N for initial contact (IC) of the foot with the force plate to toe off, respectively, defined stance phase.35 Due to a majority of noncontact injuries occurr ing in the early decelerative phase of stance, this phase was the only portion analyzed.12 For this study, the early decelerative phase was defined as IC to 20% of stance phase.145 The variables of interest were the sagittal plane angles and moments, frontal plane angles and moments, and transverse pl ane angles and moments of the hip, knee, and ankle at IC and the peak value du ring the early decelerative phase of stance. Data Reduction Excel was used to reduce each trial to stance phase. From this interval, values at IC and the peak during the early decelerative phase were identified and averaged for each trial and variable. These values were placed in a separate file. Each trial was time normalized to 100% of stance phase and be linear inter polated to 101 data points.

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42 Statistical Analysis Separate 2:g ender x 2: condition x 3: dire ction multivariate analyses of variance (MANOVA) on IC and the peak of the early decelerative phase with repeated measures on condition and direction of movement were pe rformed in the three cardinal planes ( = .05). For example, one MANOVA evaluated the effects of gender, condition, and direction on the peak and IC values of the sagittal plane (flexion/ex tension) angles of the hip, knee, and ankle.

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43 CHAPTER 4 RESULTS Preceding the description of the repeated m easures MANOVA is a gender comparison of differences in age, anthropometrics, time separating the signal delivery till first contact, and the percentage of successful trials for each particip ant. The subsequent re sults are divided into sections containing kinematics and kinetics. Each of these two sections is further divided by plane of motion and contains the main effects of condition, gender, and direction. Furthermore, significant two way and three wa y interactions are reported. Participants The 30 participants (15 m ales and 15 females) composed a sample of convenience that was recruited from undergraduate classes at the University of Florida. None of the participants had previously suffered from a lower leg injury that required surgery or were suffering from any minor injuries that may have impeded or altered performance. Of the pa rticipants, 97% reported their right leg as their dominant leg. Six inde pendent t-tests were performed to compare gender for age, height, mass, signal calibration, and percenta ge of succesful trials. The averages of these tests are shown in Table 4-1. The average age of males and females did not differ significantly (t = .989; P = .166). However, there were gender differences for height (t = 3.657; P = .001) and mass (t = 3.735; P < .001), as the males were signif icantly taller and heav ier than the females (Table 4-2). There were no signi ficant gender differences for the calibration of the light signal (t = 1.905; P = .097). Gender differences were present for the percentage of analyzed trials (t = 3.405; P = .045). See Figure 4-1 for th e failure rates of the genders.

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44 Kinematics Sagittal Plane A 2 (gender) x 2 (condition) x 2 (direction) repeated measures MANOVA revealed a significant difference among joint angles when comparing levels of anticipation (Wilks = 0.490, F (6, 23) = 3.817, P = 0.009). Univariate test s revealed that the unanticipated condition was performed with 2.2 greater hip flexion at IC (P = .003) and 2.4 at PEAK (P = .001). Sagittal plane kinematics of the lower extremity during the different anticipatory conditions are displayed in Table 4-2. No othe r significant main effects or interactions were observed. Joint angles of the hip, knee, and ankle for males and females are displayed in Table 4-3. See Table 44 for the kinematics of the joints of interest at IC and PEAK during the different cutting movements. Frontal Plane A main effect did not exist for the cond ition of movement. However, a gender main effect was detected (Wilks = 0.530, F (6, 23) = 3.400, P = 0.015). Univariate tests revealed that males performed the maneuvers with 5.7 a nd 5.6 greater hip abduction at IC (P = .011) and at PEAK (P = .019), respectively. Joint angles for males and females are shown in Table 45. A significant direction main e ffect was also observed (Wilks = 0.110, F (6, 22) = 30.930, P < 0.001). Univariate tests showed that the hip was 7.5 more abducted at IC (P < .001) and 5.6 more abducted at PEAK (P < .001). Also, the an kle was 1.0 more supinated at IC during the side cut when compared to the crossover cut (P = .027). Frontal plan e kinematics of the hip, knee, and ankle joints for the different directions appear in Table 4-6. No other main effects or interactions were detected. A ngular data for the lower extrem ity joints under the different movement conditions are di splayed in Table 4-7.

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45 Transverse Plane Direction of movement influenced jo int angles at IC and PEAK (Wilks = 0.371, F (6, 22) = 6.205, P = 0.001). At IC, the hip was interna lly rotated during the si de cut and externally rotated during the crossover cut, which lead to a joint angle difference of 6.6 (P < .001). At PEAK, the hip was internally rotated during th e side cut and externally rotated during the crossover cut yielding a difference of 9.9 (P < .001). Lower extremity kinematics comparing the different directions are re ported in Table 4-8. No othe r significant main effects or interactions were documented. Joint angles of the lower extrem ity for the different levels of anticipation appear in Table 4-9 while joint angles for males and females are shown in Table 410. Kinetics Sagittal Plane Joint moments of portions of the lower extremity were affected by the direction of movement at IC and PEAK. Joint moments differed significantly for direction (Wilks = .489, F (6, 23) = 4.004, P = .007). Univariate tests rev ealed that significant differences exist for the knee in cutting direction at PEAK and the ankle at IC. At PEAK (P = 003), the knee produced a .49 Nm/(kg*m) greater extensor moment when compared to the crossover cut (P = .003). At IC, the ankle produced a .02 Nm/(kg*m) larger plan tarflexion moment during the side cut when compared to the crossover cut (P = .003). Sa gittal plane moments of the hip, knee, and ankle joints are displayed for the diffe rent directions in Table 4-11. There were no other significant main effects or interactions. Lower extremity joint moments for males and females are shown in Table 4-12. Lower extremity joint moments of the different conditions are shown in Table 4-13.

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46 Frontal Plane A direction x condition interaction was observed (Wilks = 0.352, F (6, 23) = 7.052, P < 0.001). Follow-up tests revealed significant differences for the hip at IC and knee at IC. For the hip, the side cut was performed under both co nditions with an adduction moment at IC that was .051 Nm/(kg*m) greater during the anticipated condition. During the crossover cut, the anticipated movement was performed with an abduction moment, while the unanticipated movement was performed with an adduction moment that differed by .372 Nm/(kg*m) (P < .001). For the knee, the side cut was performed under both conditions with an adduction moment at IC that was .035 Nm/(kg*m) greater during the anticipated condition. During the crossover cut, the antic ipated movement was performed with an abduction moment, and the unanticipated movement was performed with an adduction moment that differed by .084 Nm/(kg*m) (P < .001). The joint moments of ma les and females for the hip, knee, and ankle joints are shown in Table 4-16. Several main effects and an interaction were detected at IC and PEAK. The repeated measures MANOVA revealed a main effect for condition (Wilks = 0.589, F (6, 23) = 2.678, P = 0.040). Univariate tests revealed that the jo int moment of the hip for the unanticipated condition was .016 Nm/(kg*m) greater adduction mome nt than the anticipated condition (P = .001). Joint moments for the hip, knee, and ankl e during the different conditions are shown in Table 4-14. Also, there was a main effect for direction (Wilks = 0.148, F (6, 23) = 22.010, P < 0.001). Univariate tests revealed a significant difference at the hip at IC as an adduction moment occurred during the side cut and an abduction mo ment occurred during the crossover cut yielding a .22 Nm/(kg*m) difference IC (P < .001). At PEAK, the hip joint produced an abduction moment during the side cut and an adduction mo ment during the crossover cut yielding a 1.03

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47 Nm/(kg*m) difference (P < .001). At IC, the knee joint moment for the side cut differed from the crossover cut by .06 Nm/(kg*m) due to a varus moment during the side cut and a valgus moment during the crossover cut (P < .001). At PEAK, the ankle joint produced a supination moment during the side cut and a pronation moment during the cr ossover cut giving a difference of .5 Nm/(kg*m) (P < .001). There were no other significant main effect s or interactions. Frontal plane moments of the hip, knee, and ankle jo ints for the different di rections are located in Table 4-15. Transverse Plane Main effects were present during IC and PE AK. A direction main effect was detected (Wilks = 0.518, F (6, 23) = 3.570, P = 0.012). Univaria te tests revealed that the hip was .1 Nm/(kg*m) more externally rotated during the cro ssover cut when compared to the side cut at PEAK (P < .049). At IC, the knee produced an in ternal rotation moment during the side cut and an external rotation moment duri ng the crossover cut to create a difference of .02 Nm/(kg*m) (P < .010). Furthermore, the moments of the ankle differed by .01 Nm/(kg*m) at IC as a near neutral moment was displayed during the side cu t and a external rotation moment was displayed during the crossover cut (P < .024). Joint moment s for the lower extremity during the different conditions are shown in Table 4-17. There were no other significant main effects or interactions. Transverse plane moments of the lower extremity joints across gender are located in Table 4-18. Joint moments for the different movement conditions are shown in Table 4-19. Table 4-1. The average age, height (m), mass (kg), time between the signal and IC, and the percentage of successful trials for males a nd females [* denotes significant difference at P < .05]. Data are displayed as mean SD. Gender Age Height (m)* Mass (kg)* Time (s) % of successful trials (%)* Males (N=15) 22.4 2.9 1.77 .08 76.0 9.2 0.61 0.11 48 12 Females 21.5 1.7 1.66 .08 63.8 8.8 0.68 0.11 35 20

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48 (N=15) Figure 4-1. The percentage of successful trials for male and female participants Table 4-2. Sagittal plane join t angles (degrees SD) for pr eplanned (PP) and unanticipated (UN) conditions (* denotes significan t difference at P < .05 for IC). Joint Condition IC PEAK Hip PP 48.8 7.3* 49.5 7.1 UN 51.0 7.3* 51.9 7.4 Knee PP 17.9 6.6 35.7 8.1 UN 19.0 7.5 37.2 8.4 Ankle PP 2.3 10.4 1.1 12.1 UN 2.6 11.0 -1.2 13.1 Table 4-3. Sagittal plane joint angles (degrees SD) for males and females Joint Gender IC PEAK Hip Males 51.8 6.4 52.7 6.0 Females 48.2 7.7 48.6 8.0 Knee Males 19.5 8.0 37.8 9.6 Females 17.5 6.0 35.2 6.8 Ankle Males 0.8 11.2 -1.9 13.9 Females 3.9 10.4 2.6 10.8 Table 4-4. Sagittal plan e joint angles (degrees SD) for th e side cut (Left) and crossover cut (Right) Joint Direction IC PEAK Hip Left 50.1 7.3 51.0 7.5 Right 49.7 7.3 50.4 7.1 Knee Left 17.7 6.1 37.0 6.1 Right 19.2 8.0 35.9 8.0 Ankle Left 3.5 10.8 1.3 12.6 Right 1.4 10.6 -1.3 12.7

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49 Table 4-5. Frontal plane joint angles (degre es SD) for males and females (* denotes significant difference at P < .05 for IC, de notes significant difference at P < .05 for PEAK). Joint Gender IC PEAK Hip Males -7.3 5.9* -6.6 7.5 Females -1.6 5.8* -1.0 6.8 Knee Males 5.0 6.7 10.5 12.5 Females 0.9 7.3 4.2 11.6 Ankle Males 2.0 5.5 4.9 8.1 Females 0.3 4.7 4.7 7.0 Table 4-6. Frontal plane joint a ngles (degrees SD) for the side cut (Left) and crossover cut (Right) (* denotes significant difference at P < .05 for IC, denotes significant difference at P < .05 for PEAK). Joint Direction IC PEAK Hip Left -8.1 6.0* -8.6 6.9 Right -0.6 6.7* 1.2 8.4 Knee Left 1.9 7.7 5.9 7.7 Right 3.9 7.3 8.6 6.8 Ankle Left 1.6 5.3* 4.8 7.3 Right 0.6 5.0* 4.7 7.6 Table 4-7. Frontal plane joint angles (degrees SD) for preplanned ( PP) and unanticipated (UN)(* denotes significant difference at P < .05 for IC). Joint Condition IC PEAK Hip PP -4.2 6.4 -3.7 7.5 UN -4.5 6.7 -4.0 7.8 Knee PP 2.9 7.0 7.1 11.8 UN 3.0 7.4 7.3 13.1 Ankle PP 1.2 5.1 4.9 7.2 UN 1.0 5.2 5.0 7.6 Table 4-8. Transverse plane joint angles (degrees SD) for the si de cut (Left) and crossover cut (Right) (* denotes significant difference at P < .05 for IC, denotes significant difference at P < .05 for PEAK). Joint Direction IC PEAK Hip Left 3.6 7.2* 9.3 9.3 Right -3.0 9.6* -0.6 8.4 Knee Left -2.9 6.6 7.7 6.6 Right -2.6 8.1 9.1 8.1 Ankle Left -6.7 10.2 -19.1 9.6 Right -3.8 9.9 -18.6 9.5

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50 Table 4-9. Transverse plane joint angles (degrees SD) for males and females Joint Gender IC PEAK Hip Males 2.2 9.5 6.4 9.2 Females -1.4 7.6 2.5 9.6 Knee Males -2.9 7.4 3.6 9.3 Females -2.6 7.5 12.9 9.6 Ankle Males -7.6 8.9 -17.4 8.2 Females -3.0 9.1 -20.2 9.1 Table 4-10. Transverse plane join t angles (degrees SD) for prep lanned (PP) and unanticipated (UN) conditions Joint Condition IC PEAK Hip PP -0.3 8.7 4.0 8.1 UN 0.9 9.7 4.8 9.6 Knee PP -2.7 7.0 8.3 7.4 UN -2.8 7.6 8.4 7.6 Ankle PP -5.3 9.0 -19.0 8.4 UN -5.1 9.1 -18.7 8.3 Table 4-11. Sagittal plane joint moments (Nm/(kg*m) SD) for the side cut (Left) and crossover cut (Right) (* denot es significant difference at P < .05 for IC, denotes significant difference at P < .05 for PEAK). Joint Direction IC PEAK Hip Left 1.26 0.64 2.31 0.86 Right 1.33 0.45 2.19 0.72 Knee Left -0.54 0.30 0.58 0.30 Right -0.58 0.28 0.09 0.29 Ankle Left 0.04 0.08* 0.52 0.60 Right 0.02 0.08* 0.47 0.48 Table 4-12. Sagittal plane joint moments (Nm/(kg*m) SD) for males and females Joint Gender IC PEAK Hip Males 1.27 0.54 2.41 0.66 Females 1.32 0.52 2.09 0.70 Knee Males -0.61 0.30 0.63 0.35 Females -0.51 0.29 0.59 0.38 Ankle Males 0.04 0.10 0.51 0.57 Females 0.02 0.04 0.46 0.50 Table 4-13. Sagittal plane joint moments (Nm/(kg*m) SD) for preplanned (PP) and unanticipated (UN) conditions. Joint Condition IC PEAK Hip PP 1.24 0.43 2.25 0.80 UN 1.35 0.52 2.22 0.85 Knee PP -0.56 0.25 0.37 0.46 UN -0.56 0.33 0.35 0.52

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51 Ankle PP 0.02 0.07 0.49 0.51 UN 0.04 0.08 0.48 0.57 Table 4-14. Frontal plane joint moments (N m/(kg*m) SD) for preplanned (PP) and unanticipated (UN) conditions (* denotes si gnificant difference at P < .05 for IC). Joint Condition IC PEAK Hip PP 0.01 0.43* 0.21 0.35 UN 0.17 0.48* 0.24 0.31 Knee PP -0.01 0.17 0.62 0.45 UN 0.02 0.16 0.62 0.46 Ankle PP 0.01 0.03 0.10 0.20 UN 0.01 0.02 0.11 0.21 Table 4-15. Frontal plane joint mo ments (Nm/(kg*m) SD) for the side cut (Left) and crossover cut (Right) (* denotes significant differen ce at P < .05 for IC, denotes significant difference at P < .05 for PEAK). Joint Direction IC PEAK Hip Left 0.19 0.45* -0.34 0.49 Right -0.03 0.50* 0.69 0.54 Knee Left 0.04 0.15* 0.49 0.15 Right -0.02 0.17* 0.75 0.17 Ankle Left 0.01 0.02 0.35 0.12 Right 0.01 0.03 -0.15 0.19 Table 4-16. Frontal plane joint moments (N m/(kg*m) SD) for males and females. Joint Gender IC PEAK Hip Males -0.04 0.43 -0.18 0.56 Females 0.20 0.45 0.53 0.59 Knee Males 0.03 0.17 0.45 0.38 Females 0.05 0.15 0.79 0.39 Ankle Males 0.01 0.03 0.08 0.15 Females 0.01 0.01 0.14 0.23 Figure 4-2. Direction x c ondition interaction for hip joint moments at IC

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52 Figure 4-3. Direction x c ondition interaction for knee joint moments at IC Table 4-17. Transverse plane moments (N m/(kg*m) SD) for preplanned (PP) and unanticipated (UN) conditions (* denotes significant difference at P < .05 for IC, denotes significant difference at P < .05 for PEAK). Joint Direction IC PEAK Hip Left -0.01 0.04 -0.10 0.02 Right -0.01 0.01 -0.20 0.06 Knee Left 0.01 0.03* 0.05 0.03 Right -0.01 0.03* 0.09 0.03 Ankle Left 0.00 0.03* -0.07 0.05 Right -0.01 0.03* -0.03 0.09 Table 4-18. Transverse plane joint moments (Nm/(kg*m) SD) for males and females. Joint Gender IC PEAK Hip Males -0.02 0.04 -0.12 0.17 Females -0.01 0.04 -0.18 0.15 Knee Males -0.01 0.03 0.07 0.13 Females 0.01 0.02 0.07 0.11 Ankle Males -0.01 0.03 -0.05 0.15 Females 0.00 0.02 -0.04 0.12 Table 4-19. Transverse plane joint moments (Nm/(kg*m) SD) for preplanned (PP) and unanticipated (UN) conditions. Joint Condition IC PEAK Hip PP -0.02 0.04 -0.16 0.16 UN -0.01 0.05 -0.13 0.15 Knee PP 0.00 0.03 0.07 0.12 UN 0.00 0.02 0.07 0.12 Ankle PP -0.01 0.03 -0.05 0.14 UN 0.00 0.03 -0.04 0.16

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53 CHAPTER 5 DISCUSSION Females are four to six times more likely to suffer an ACL injury than men when playing the same sports.5-8 Gender differences during antic ipated cutting are well documented.35, 42, 121, 183 Due to the limitations of extrapolating da ta collected during anticipated movements to competition, more researchers have utilized unanticipated movements in their research. Although some comparisons betwee n anticipated movements and unanticipated movements have been reported, cutting movements have not been compared under anticipated and unanticipated conditions with a sample composed of both males and females. Therefore, the purpose of this study was to investigate the eff ects of anticipation and gender on the lower extremity during high risk cutting movements. Although the statistical tests used in this study were de lineated by cardinal plane and biomechanical measure, the interaction of the lowe r extremity joints in all planes of movement seems to produce the most deleterious effects with respect to ACL injury rates.192 Therefore, comparisons of cutting condition, gender, and the diffe rent movement directi ons will be detailed in separate sections. Condition comparisons will be emphasized due to the dearth of published research relating condition effects on males and females. Although the relationship among drop jumps and cutting tasks utilized in laboratory research is not well understood, 127, 183 condition comparisons of drop jumps will be included due to the lack of research comparing anticipated and unanticipated conditions while utilizing cutting movements. Participants The particip ants were college aged underg raduate students who composed a sample of convenience. The height and mass of the participants41, 142 and the sample size was similar to other previously reported samples of convenience.42, 54, 160, 174, 193 Due to significant gender

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54 differences in height and mass, joint moments were normalized to the height and mass of each subject. In order to ensure that trials for each condi tion and direction could be analyzed, many of the participants attempted more than the required 30 trials. Although the number of analyzed trials did not differ significantly between genders, the percentage of successful trials was significantly different due to th e males requiring less trials to acquire a similar number of analyzed trials as the females. Although the ma les were more adept at performing the cutting movements, both groups had a failure rate of more than 50%. The high failure rates are likely a combination of the relatively low skill inherent with samples of convenience and the difficulty of performing the cutting movements with the required approach speed. A trade off between speed and accuracy occurred as many participants were unable to consistently accelerate to the proper speed and cleanly plant on the force plate. Due to most researchers not reporting the number of analyzed trials, difficulty exists when compari ng our number of succesful trials to previously published literature. Condition Sagittal Noncontact ACL injuries purportedly occur dur ing m ovements with de creased flexion at the hip and knee.12, 13 Performance of sporting activities with decreased hip and knee flexion may prevent the hamstring from aiding the ACL in resisting anterior movement of the tibia relative to the femur.121, 182 Due to less than optimal spatial orientation prior to performance of the athletic movement and a decreased time to appropriately position th e body, an unanticipated movement would be more likely to produce an alignment which is less safe for ACL injury.136 Similarly, Besier et al.184 reported increased knee flexion angl es for the unanticipated condition. Counter to our hypothesis, unanticipated movements were performed with an increased hip

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55 flexion at IC and at PEAK when compared to the anticipated condition. Compensation for unanticipated movements in a controllable la b setting may occur through lowering the COM height and producing a less dangerous movement pattern. An increased chance of injury may arise when compensation is unattaina ble due to temporal restrictions.184 Frontal Since greater knee valgus m oments and GRFs occur through an incr ease in medial knee motion, frontal plane biomechanical measures are extremely important.111 Furthermore, frontal plane knee joint angles have been used to predict future ACL injuries, and continuous performance of athletic movements with incr eased frontal plane movements may increase the possibility of ACL injury.12, 21 Direction x condition interactions were revealed for the hip and knee in the frontal plane. The side cut wa s performed with hip a nd knee adduction moments under both conditions, while the crossover cut was performed with hip and knee abduction moments during the preplanne d condition and hip and knee adduction moments during the unanticipated condition. In order to perfor m the movements during the unplanned condition, participants used hip and knee adduction moments during the unanticipated movements. Due to similar moments used during the different direct ions under unanticipated conditions, participants were unable to accommodate to the unanticip ated movements in the frontal plane. Although no significant differences were found for the influence of anticipation on frontal plane kinematics, significant differences in jo int moments were present at IC for the hip. Unanticipated movements were performed with greater hip adduction moments. Hip adduction is a primary component of dynamic valgus and previously correlated wi th knee valgus during drop landings.21 Knee abduction was not revealed in our results. Thus, the predictive nature of knee abduction during drop jumps may not apply to cutting movements. Besier et al.184 reported knee valgus moments increased when compari ng anticipated movement s to unanticipated

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56 movements. Frontal plane hip and knee joint differences have been published during cutting movements, as unanticipated movements were performed with increased knee abduction angles.174, 194 Also, a visual inspection of the Boro tikar study revealed that 58% more knee abduction occurred in the joint angles of the nondominant leg when comparing unanticipated movements to anticipated movement. In our sa mple, 97% of the participants performed the cutting movements using their dominant leg, whic h may help to explain the disparity among the studies. Transverse Increased hip internal rotation pot en tially places the lower extremity in an alignment that is less safe.151 Furthermore, increased rotation and adduction at the hip when coupled with decreased glute medius strength may produce increased knee valgus angles.195 However, no significant differences were found in the kinetic s or kinematics of the lower extremity when comparing conditions in the tran sverse plane. Brown et al.194 did not find signi ficant differences in the kinematics of the knee and hip, but show ed that unanticipated movements resulted in increased internal rotation mo ments of the hip and knee. In addition, Borotikar et al.174 showed that the condition of movement can modify transv erse plane kinematics at the hip and knee, as the dominant and nondominant leg became more in ternally rotated at the hip and ankle. Performance of an unanticipated side cut increas ed the internal rotation moment of the knee in early stance phase.184 Differences among studies may be due to our sample being the least skilled, yet performing one of the more difficult tasks to consisten tly execute due to such a high approach speed. Although unanticipated movements are increasingly being inco rporated into controlled research, differences exist between the lab setting and competiti on. The present study incorporated acceleration towards a predetermine location followed by pivoting with the right leg

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57 and performance of one of the three movement op tions. In competition, at hletes rarely change direction at a predetermined area with so few options regarding di rection of movement and plant leg. Due to the vast differences in unpred ictability between competition and lab settings, whether truly unanticipated movements were utilized in this study is questi onable. However, the similar moments at the hip and knee for the unp lanned conditions are an interesting finding suggesting that anticipation was prevented and a similar movement pattern was utilized. The success and ecological validity of future stud ies hinges upon improvement in techniques to prevent anticipation such as uti lizing an increased num ber of movement opti ons, delivery of the signal through more sophisticated means, or delivery of multiple signals during different phases of the gait cycle. Therefore, discrepancies among studies are an expected occurrence due to differing methods of anti cipation prevention. Gender Sagittal Fe males have been described as performing athl etic movements with an internally rotated and adducted hip, decreased flexion and valgus at the knee, and ankle eversion. Gender differences exist during running, jump landings, and cutting ma neuvers. Gender differences have been documented during various athletic movements with females using less hip and knee flexion when compared to males.42, 121, 182 However, the present gender comparisons for kinematics and kinetics of the sagittal plane did no t replicate the results of previous studies. Due to the plethora of gender difference data during various movements, our results are surprising. However, few researchers have utilized our appr oach speeds, and the ones that did recruited mostly college soccer players. 122, 145, 150, 151, 196 To our knowledge, this is the first study with a sample composed of recreational college unde rgraduates to perform cutting movements at approach speeds greater than 5.5 m/s. Furthermor e, our participants did not reach the required

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58 speed until after the signal for the cutting m ovement. Although the process of performing a movement amidst accelerations and deceleratio ns more closely simulates competition than anticipated cutting, the o ccurrence of this process at the required speed may have prevented variation in movement strategies due to venturing toward the limits of the samples cutting ability. Frontal Previously, f emales consistently differed in fr ontal plane measures of the lower extremity. In the current study, females performed the cutting movements with less hip abduction at the hip at IC and at PEAK. Instead of relying on the sagittal plane for force dissipation, females tend to rely more on the frontal and transverse planes.151 Decreased abduction may be due to lacking strength in the hip abductors su ch as the glute medius. Altho ugh no significant differences at the knee were present, increased knee valgus of fe males while performing cutting maneuvers is well documented.42, 121, 134, 183 The results of the current study were very similar to a previous study which involved the investigation of a side cut, stop jump, and a r un with analysis of stance phase across the first 40 of knee flexion.151 Similarly, significant gende r differences in peak hip abduction during the early decelerative phase of cutting maneuvers have been reported. 151 Transverse Increased hip internal rotation angles ha ve been found for fe males during cutting movements.145 Also, hip internal rotation at IC positively correlated with peak knee abduction.183 Results for peak knee valgus in the curre nt study were similar to the peak knee valgus moments of McLean et al.183 However, the females in our sample performed cutting movements with external rotation at IC, not inte rnal rotation. Differences exist between studies as their sample used slower approach speeds but was composed of more skilled college athletes. Increased approach speeds in the current study ma y be the reason for our increased knee valgus

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59 moments but would not explain why a less skilled sample perf orming a more difficult task utilized a safer alignment. As was noted prev iously, the relatively low skill of our sample performing the high risk movements at a greater speed may have prevente d variation in cutting strategy due to the analysis of only the successful trials. Direction changes during competition can occu r at velocities ranging between 5.5 and 7 m/s.191 For the current study, an approach speed of 5.5 to 7 m/s was selected to use the lab setting to test cutting movements at speeds en countered during competition. Although approach speeds similar to the current study have been pr eviously employed during research, the majority of the samples used in those studies contained college athlet es with the only sample not composed of college athletes be ing competitive high school athletes.122, 145, 150, 151, 196 Therefore, the sample of convenience used in the current study was composed of relatively less skilled recreational college aged participants. Due to the stringent requirements necessary for the analysis of trials, a homogenizing effect on the data may have o ccurred. Theoretically, college athletes proficient at cutting would be more skilled performing the movements at higher speeds and may self select a greater approach speed th an would a less skille d person. Naturally, the skilled athlete would be more pr oficient during change of direc tion and utilize a safer alignment at higher speeds. Therefore, the high approach speed necessary for analysis may have allowed for fewer acceptable cutting strategies for partic ipants of either gender to complete the movements. Presumably, this may have negated any gender differences. Direction Sagittal Change in direction occurs through f oot pl acement lateral to th e center of mass and opposite the direction of movement and incorporates a decrease in velocity over several gait cycles prior to cutting.181 Previously, the side cut was docum ented as being more effective at

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60 producing changes in direction.197 Although both movements in the current study were performed within the previously specified speed range, differences were present in sagittal plane moments for the knee at PEAK and ankle at IC. From a previous study, the vastus medialis, a knee extensor, and the gastrocnemius produced a greater activation during the side cut when compared to the crossover cut.197 During early stance, lower extremity extensor moments absorb the force of movement.42, 198 Therefore, greater extensor mome nts during early stance are due to increased momentum during the pivo ting step of the side cut. Based on subjective observation, accommodation for the crossover cut seemed to occur with the participants absorbing most of the mome ntum with the step prece ding the crossover cut. In addition, many participants commented on the di fficulty of performing th e crossover cut at the required approach speed. Sagittal knee and ankl e moment data corroborate our observations that participants required less fo rce absorption during the crossover cut than the side cut. Performance of a crossover cut without the prece ding step to safely decrease momentum may increase the possibility of an ACL injury as the alignment during a crossover cut more closely simulates the mechanism of valgus collapse seen during ACL injuries due to hip adduction required to propel the center of mass in the opposite direction of foot placement.42 Successful performance of the correct movement requires delivery of the stimulus to occur two steps prior to performi ng either cutting maneuver.197 Due to our contention that the crossover cut was performed with a preceding side cut, the signal occurred less than two steps prior to changing directio ns. Our findings may be different th an previous work because this is the first study to compare side cutting and crossover cutting at approach speeds over 5.5 m/s. Our protocol for calibrating the timing of the s timulus required participants to successfully perform both movements at that specified time, but we did not separately document the timing

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61 for each movement. Therefore, it is unknown wh ether differences in the timing of the signal exist for both movements. Requiring the signal to be two steps or more pr ior to contact with the force plate may have been due to limitations of perf orming the crossover cut and not the side cut. Although our results support the timing of the stimulus being two steps prior to IC, further investigation is required to locate the timing of the stimulus in relation to both the crossover cut and side cut. Frontal Frontal plane kinem atics and kine tics differed during the side cut and the crossover cut. The dangerous frontal plane alignment for noncont act injuries usually contains hip adduction, knee valgus, and ankle eversion. Though neither direction completely coordinated with the deleterious alignment, the kinetics of the crossover cut seem to be more perilous due to hip adduction moment at PEAK, knee abduction moment at IC, and a pronation ankle moment at PEAK. When the kinetics are coupled with an adducted hip angle at PEAK, a crossover cut seems to produce a movement pattern more sim ilar to the proposed ACL noncontact injury mechanism than the side cut. Transverse In the transverse plane, the m ore dangerous alignment for an ACL injury is an internal rotation angle at the hip. In the current study, the side cut was perf ormed with internal rotation at the hip at IC and PEAK. Although an external rotation moment during the side cut does not seem to be injurious to the ACL, when coupled w ith an internal rotation moment at the knee, an increased chance of injury may exist due to th e joints having moments in opposite directions. Conversely, the crosscut was perfor med with external rotation moment s at all joints of the lower extremity. In the transverse plane, the side cut seems to be a more dangerous movement.

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62 To change direction, lateral placement of the center of pressure (COP) to the center of mass (COM) is required.199 The side cut has been documented as being more effective at change of direction due to retaini ng a greater velocity when compared to the crossover cut.197 Our results confirm the effectiveness of the side cut ov er the crossover cut, as the performance of the crossover cut at high speeds seems to only be accomplished through decreasing momentum in the preceding step. Furthermore, the crossove r cut seems to be more dangerous due to knee abduction and ankle pronation and the require d hip adduction to perform the maneuver. Limitations The purpose of this study was to use unanticipated m ovements to more closely simulate competition in order to provide an improved understanding of biomechanical measures in relation to ACL injury and compare this more re alistic data to controlle d research. Logically, unanticipated movements would seem to be mo re relatable to competition than anticipated movements. However, it is questionable just how similar to competition the laboratory setting is. During competition, athletes are constantly asse ssing the location and sp atial orientation of members of both teams in addition to the ball while coordinating their own movements to perform a variety of accelerations and decelerati ons. Conversely, this study entailed only one movement from one stimulus during each trial. Although the participants did not know what specific direction to move, only th ree choices were available: cut left, straight, or cut right. Therefore, the level of relatedness of this study to cutting in actual comp etition encountered in soccer or basketball is debatable. However, util ization of unanticipated movements in laboratory studies is important to more cl osely simulate competition. Similarly, the location and design of the light signal system may have proved a limiting factor. The exact location of the light signal system is often not provided in the literature. Few have reported exact distances, wh ile most opt for an overhead pict ure of the entire lab space.

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63 What influence the location of th e light stimulus may have on the results is unclear. Also, the design of the light signal system may be not be conducive to recognizing the correct signal during sprint movements. Central processing must occur in order to see the cue, process the information, and employ the proper movement pa ttern. Therefore, the signal produced by our light system may not have been as easily recognized as the use of a runway lined with a string of lights or an approaching obstacl e to be avoided. Furthermore, the lapse of time between the delivery of the signal and contact with the fo rce plate is not reported for unanticipated movements. Therefore, difficulty exists for making comparisons within the literature for skill discrepancies pertaining to specific athletic tasks across samples. Our analysis consisted only of successful tria ls with the correct speed, angle, movement, and successfully placing the right foot on the fo rce plate. Our sample was composed of recreationally active undergraduate students, which lead to a range in skil l levels and experience with the cutting movements. The success rates for males and females were over 60% and 74%, respectively. However, there was variability in the skill of the sample; six of the participants completed less than 50% of the trials. Due to this discrepancy in skill a nd stringent requirements for trials to be analyzed, the participants may have utilized similar movement patterns in the successful trials. Of the failed trails, 67% were not analyzed due to the improper placement of the entire foot on the force plate, and 16% we re not analyzed due to performing the cutting maneuver out of the required range It is unknown how the kinematics and kinetics of the unsuccessful trials compare to t hose of the successful trials. Another potential limitation would be the relatively small percentage of stance utilized for analysis. For this project, data were analyzed at IC and the first 20% of stance. Early decelerative phase is the porti on of stance for which most noncontact ACL injuries occur.12

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64 However, it is unknown at exactly wh at percentage of stance most in juries occur, what interval of stance would contain most injuri es, or at what percentage of st ance for which the risk of injury dramatically decreases. Lack ing a better understanding of the st ance interval containing most injuries produced the investigation of a variet y of measurements duri ng different periods of stance. Variation in results among studies may be partially attributed to discrepancies in the portion investigated during stance. Therefore, furt her research is necessary to clarify the portion of stance which contains most injuries. In this study, 97% of the pa rticipants performed the cu tting movements with their dominant leg. Analysis of onl y one leg was undertaken to simplify the calculations of the reported biomechanical measures. Leg dominan ce, a significant stre ngth and flexibility discrepancies between legs, is well documented in females, and athletes w ith significant strength and flexibility imbalances between legs have higher injury rates.110-112 Previously, researchers showed greater knee abduction in the nondominant leg.174, 194 Therefore, testing the dominant and nondominant leg may have provided a better understanding of how the e ffects of anticipation can alter biomechanical measures of the lower extremity. According to Winter,200 two strategies exist for cha nging direction during locomotion: control during swing phase of the COP through f oot placement (swing strategy) or control during stance using hip and ankle musculature (stan ce strategy). Differentiation between COM and COP dictate the acceleration and direction of the movements. For example, performance of a side cut occurs through placing the COP farther to the right of the norma l foot placement when running straight. Utilization of the stance strategy occurs thr ough recruitment of hip and ankle musculature to change direction. Due to variet y in the timing of stim uli during locomotion, the reliance on either strategy will exist on a continuum. In theory, utilization of the swing strategy

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65 would be more prevalent during preplanned move ments. An individual would preplan the placement of the COP location. During unplanne d movements, a greater reliance on stance strategy would be required due to temporal restrictions. Due to a combination of change of direction and braking, the forced reliance on stance strategy to ch ange direction may prove to generate greater forces than the lower extremity can safely dissipate. This may help explain the gender differences in ACL injury rates since fema les have a lower baseline of strength due to focus on improved strength during prevention programs improving the gender differences in ACL injury rates.124, 167 Conclusion Investigatio n into causes of th e gender discrepancy in ACL inju ry rates has garnered much attention with little improvement. This study repr esents the first attempt at investigating the anticipatory effects of cutting m ovements on the lower extremity using a sample composed of males and females. Also, this is the first project to use approach speeds greater than 5.5 m/s with a sample composed of college ag ed recreational athletes. Due to the combination of a relatively low skilled sample and difficult tasks, failure rates exceeded 50%. Unanticipated movements were performed with incr eased hip flexion angles and greater hip adduction moments. Similar to results from previous studies, participants acco mmodated for lacking the time to plan movements by utilizing a more versatile pos ture for cutting through decreasi ng the height of the COM and using similar moments at the hip and knee in the frontal plane. These accommodations show the difficulty of preventing anticipation in the lab setting. However, increased hip adduction moments were utilized during th e unanticipated condition. Hip adduction is a component of dynamic valgus, the purported injury mechanism fo r ACL injury. Since recreational athletes possess the capacity to safely alter movement pa tterns during unanticipated conditions in the lab

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66 setting, two recommendations can be made. Firs t, improvements for preventing anticipation in experiments are necessary to fu rther understand how movements are controlled when lacking the time to preplan. Second, unanticipated moveme nts should be incorporated into training programs with anticipated movements. The co mbination of using anticipated movements to teach correct alignment may provide a carryover a ffect into unanticipated movements. Although our results provide positive evidence for the in corporation of unanticip ated movements into training programs, further investigation is requi red under more diverse conditions and utilizing different movements. For the present study, gender differences were found only in the frontal plane hip kinematics. With the high failure rates, the possi bility exists that we unintentionally biased our results due to only processing th e successful trials Although the stringent requirements may have pushed the sample to the limits of thei r capacity to successfully change direction, a successful performance may have necessitated a si milar movement strategy for both genders. In order for a trial to be analyze d, the kinematics and kinetics em ployed by participants may have been required to be similar. Therefore, we recommend the incorporation of unsuccessful trails into the analysis of future studies. Regarding ACL injury, the crossover cut seem ed to produce a more deleterious alignment than the side cut due to incr eased knee abduction and ankle pronation. Similarly, the crossover cut seemed to have only been successfully performed by decreasing momentum through the performance of a preceding side cut. The ramifica tions of this development are twofold. First, ACL injury seems more likely to occur during a cr ossover cut that lacks a preceding side cut to safely decrease the momentum of movement. Second, these results would disagree with the assertion that a signal for moveme nt must be displayed at least two steps prior to a change in

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67 direction. Although the crossover cut seems to be less safe due to performance with a preceding accommodation step at high speeds, the side cut s eems to be a more popular choice for research as more examples exist of the side cut in pr evious studies. Therefore, we recommend more investigation of the crossover cut related to ACL injury.

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68 APPENDIX A MANOVA TABLES FOR NONS I GNIFICANT RESULTS Kinematics Sagittal Com parison Wilks F value P value Gender 0.685 1.690 0.171 Direction 0.615 2.299 0.071 Condition Gender 0.836 0.719 0.650 Condition Direction 0.804 0.895 0.516 Direction Gender 0.738 1.359 0.272 Gender Condition Direction 0.781 1.074 0.407 Frontal Com parison Wilks F value P value Condition 0.921 0.316 0.921 Condition Gender 0.888 0.464 0.827 Condition Direction 0.549 3.153 0.221 Direction Gender 0.905 0.400 0.871 Gender Condition Direction 0.717 1.510 0.219 Transverse Com parison Wilks F value P value Condition 0.803 0.899 0.513 Gender 0.766 1.121 0.382 Condition Gender 0.729 1.426 0.247 Condition Direction 0.686 1.755 0.153 Direction Gender 0.720 1.437 0.244 Gender Condition Direction 0.710 1.565 0.202 Kinetics Sagittal Com parison Wilks F value P value Gender 0.726 1.445 0.241 Condition 0.726 1.448 0.240 Condition Direction 0.645 1.798 0.189

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69 Condition Gender 0.882 0.514 0.792 Direction Gender 0.793 1.003 0.447 Gender Condition Direction 0.802 0.949 0.480 Frontal Com parison Wilks F value P value Gender 0.662 1.956 0.114 Condition Gender 0.898 0.436 0.847 Direction Gender 0.823 0.827 0.561 Gender Condition Direction 0.654 2.025 0.103 Transverse Com parison Wilks F value P value Condition 0.758 1.225 0.330 Gender 0.780 1.081 0.403 Condition Gender 0.934 0.270 0.945 Condition Direction 0.934 0.270 0.100 Direction Gender 0.817 0.859 0.539 Gender Condition Direction 0.786 1.043 0.424

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70 APPENDIX B JOINT ANGLES AND MOMENTS a) b) c) d) e) f) g) h) i) Figure B-1. Joint angles during stance phase for males (dotted, blue line) and females (solid, orange line) for a) hip sagittal plane b) hi p frontal plane c) hip transverse plane d) knee sagittal plane e) knee frontal plane f) knee transverse plane g) ankle sagittal plane h) ankle frontal plane i) ankle transverse plane

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71 a) b) c) d) e) f) g) h) i) Figure B-2. Joint moments during stance phase fo r males (blue line) and females (orange line) for a) hip sagittal plane b) hip frontal plan e c) hip transverse pl ane d) knee sagittal plane e) knee frontal plane f) knee transverse plane g) ankle sagi ttal plane h) ankle frontal plane i) ankle transverse plane

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72 a) b) c) d) e) f) g) h) i) Figure B-3. Joint angles during st ance phase for side cut (dotte d, blue line) and crossover cut (solid, orange line) for a) hip sagittal plane b) hip frontal plane c) hip transverse plane d) knee sagittal plane e) knee frontal plane f) knee transverse plane g) ankle sagittal plane h) ankle frontal plane i) ankle transverse plane

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73 a) b) c) d) e) f) g) h) i) Figure B-4. Joint moments during stance phase for si de cut (orange line) and crossover cut (blue line) for a) hip sagittal plane b) hip front al plane c) hip tran sverse plane d) knee sagittal plane e) knee frontal plane f) knee tr ansverse plane g) ankle sagittal plane h) ankle frontal plane i) ankle transverse plane

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74 LIST OF REFERENCES 1. Girgis FG, Marshall JL, Monajem A. Crucia te Ligaments of Knee -Joint Anatomical, Functional and Experimental Analysis. Clinical Orthopaedics and Related Research. 1975(106):216-231. 2. Butler DL, Noyes FR, Grood ES. Ligamentous Rest raints to Anterior-Posterior Drawer in the Human Knee Biomechanical Study. Journal of Bone and Joint Surgery-American Volume. 1980;62(2):259-270. 3. Amis AA, Dawkins GPC. Functional-Anatomy of the Anterior Cruciate Ligament Fiber Bundle Actions Related to Ligament Replacements and Injuries. Journal of Bone and Joint Surgery-British Volume. Mar 1991;73(2):260-267. 4. Griffin LY, Agel J, Albohm MJ, et al. Noncontact anterior cr uciate ligament injuries: risk factors and prevention strategies. J Am Acad Orthop Surg. 2000;8(3):141-150. 5. Daniel DM, Stone ML, Dobson BE, Fithian DC, Rossman DJ, Kaufman KR. Fate of the Acl-Injured Patient a Prospective Outcome Study. American Journal of Sports Medicine. 1994;22(5):632-644. 6. Huston LJ, Greenfield M, Wojtys EM. Anterior cruciate ligament injuries in the female athlete Potential risk factors. Clinical Orthopaedics and Related Research. 2000(372):50-63. 7. Arendt EA, Agel J, Dick R. Anterior cr uciate ligament injury patterns among collegiate men and women. Journal of Athletic Training. 1999;34(2):86-92. 8. Messina DF, Farney WC, DeLee JC. The in cidence of injury in Texas high school basketball A prospective study am ong male and female athletes. American Journal of Sports Medicine. 1999;27(3):294-299. 9. Goodman LRW, M. P. The female athlete and menstrual function. Current Opinion in Obstetrics and Gynecology. 2005;17:466. 10. Hewett TE, Ford KR, Myer GD. Anterior cruciate ligament injuries in female athletes Part 2, a meta-analysis of neuromuscular interventions aimed at injury prevention. American Journal of Sports Medicine. 2006;34(3):490-498. 11. Silvers HJ, Mandelbaum BR. Prevention of an terior cruciate ligament injury in the female athlete. British Journal of Sports Medicine. August 1, 2007 2007;41(suppl_1):i5259. 12. Boden BP, Dean GS, Feagin JA, Garrett WE. Mechanisms of anterior cruciate ligament injury. Orthopedics. Jun 2000;23(6):573-578.

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75 13. McNair PJ, Marshall RN, Matheson JA. Im portant Features Associated with Acute Anterior Cruciate Ligament Injury. New Zealand Medical Journal. 1990;103(901):537539. 14. Olsen OE, Myklebust G, Engebretsen L, Bahr R. Injury mechanisms for anterior cruciate ligament injuries in team handba ll a systematic video analysis. American Journal of Sports Medicine. 2004;32(4):1002-1012. 15. Ireland ML. Anterior cruciate ligament in jury in female athletes: Epidemiology. Journal of Athletic Training. 1999;34(2):150-154. 16. Tillman MD, Hass CJ, Brunt D, Bennett GR Jumping and landing techniques in elite women's volleyball. Journal of Sports Science and Medicine. 2004;3(1):30-36. 17. Hewett TE, Paterno, M. V., & Myer, G. D. Strategies for enhancing proprioception and neuromuscular control of the knee. Clinical Orthopaedics and Related Research. 2002;402:76-94. 18. Renstrom P, Ljungqvist A, Are ndt E, et al. Non-contact ACL injuries in female athletes: an International Olympic Committ ee current concepts statement. British Journal of Sports Medicine. 2008;42(6):394-412. 19. Bonci CM. Assessment and evaluation of predisposing factors to anterior cruciate ligament injury. Journal of Athletic Training. 1999;34(2):155-164. 20. Hewett TE, Myer GD, Ford KR. Anterior cruciate ligament injuries in female athletes Part 1, mechanisms and risk factors. American Journal of Sports Medicine. 2006;34(2):299-311. 21. Hewett TE, Myer GD, Ford KR, et al. Biomech anical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes. American Journal of Sports Medicine. 2005;33(4):492-501. 22. Hughes G, Watkins J. A risk-factor mode l for anterior cruciate ligament injury. Sports Medicine. 2006;36(5):411-428. 23. Lohmander LS, Ostenberg A, Englund M, Roos H. High prevalence of knee osteoarthritis, pain, and functional limitations in female soccer play ers twelve years after anterior cruciate ligament injury. Arthritis and Rheumatism. 2004;50(10):3145-3152. 24. Besier TF, Lloyd DG, Cochrane JL, Ackla nd TR. External loadi ng of the knee joint during running and cutting maneuvers. Medicine and Science in Sports and Exercise. 2001;33(7):1168-1175. 25. Hamill J, Knutzen, K. M. Bioimechanical Basis of Human Movement Philladelphia: Lippincott Williams & Wilkins; 2003.

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76 26. Zantop T, Petersen W, Sekiya JK, Musahl V, Fu FH. Anterior cruciate ligament anatomy and function relating to an atomical reconstruction. Knee Surgery Sports Traumatology Arthroscopy. 2006;14(10):982-992. 27. Markolf KL, Mensch JS, Amstutz HC. Stiffn ess and Laxity of Knee Contributions of Supporting Structures Quantitative Invitro Study. Journal of Bone and Joint SurgeryAmerican Volume. 1976;58(5):583-594. 28. Norwood LA, Cross MJ. The intercondylar sh elf and the anterior cruciate ligament. Am J Sports Med. 1977;5(4):171-176. 29. Duthon VB, Barea C, Abrassart S, Fasel JH, Fritschy D, Menetrey J. Anatomy of the anterior cruciate ligament. Knee Surgery Sports Traumatology Arthroscopy. 2006;14(3):204-213. 30. Chhabra A, Starman JS, Ferretti M, Vidal AF, Zantop T, Fu FH. Anatomic, radiographic, biomechanical, and kinematic evaluation of th e anterior cruciate ligament and its two functional bundles. Journal of Bone and Joint Surgery-American Volume. 2006;88A:210. 31. Xerogeanes JW, Takeda Y, Livesay GA, et al Effect of knee flexion on the in situ force distribution in the human an terior cruciate ligament. Knee Surg Sports Traumatol Arthrosc. 1995;3(1):9-13. 32. Hollis JM, Takai S, Adams DJ, Horibe S, Woo SLY. The Effects of Knee Motion and External Loading on the Length of the Anteri or Cruciate Ligament (Acl) a Kinematic Study. Journal of Biomechanical Engineering-Transactions of the Asme. 1991;113(2):208-214. 33. Georgoulis AD, Papadonikolak is A, Papageorgiou CD, Mitsou A, Stergiou N. Threedimensional tibiofemoral kinematics of the an terior cruciate ligament-deficient and reconstructed knee during walking. American Journal of Sports Medicine. 2003;31(1):7579. 34. Harner CD, Baek GH, Vogrin TM, Carlin GJ, Kashiwaguchi S, Woo SLY. Quantitative analysis of human cruciate ligament insertions. Arthroscopy-the Journal of Arthroscopic and Related Surgery. 1999;15(7):741-749. 35. Ford KR, Myer, G. D., Toms, H. E., & Hewett, T. E. Gender differences in the kinematics of unanticipated cutting in young athletes. Medicine and Science in Sports and Exercise. 2005;37:124-129. 36. Hurd WJ, Chmielewski TL, Axe MJ, Davis I, Snyder-Mackler L. Differences in normal and perturbed walking kinematics be tween male and female athletes. Clinical Biomechanics. 2004;19(5):465-472.

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77 37. Chaudhari AM, Andriacchi TP. The mechani cal consequences of dynamic frontal plane limb alignment for non-contact ACL injury. Journal of Biomechanics. 2006;39(2):330338. 38. Bellchamber TL, van den Bogert AJ. Contri butions of proximal a nd distal moments to axial tibial rotation duri ng walking and running. Journal of Biomechanics. 2000;33(11):1397-1403. 39. Perry SD, Lafortune MA. Influences of I nversion Eversion of the Foot Upon Impact Loading During Locomotion. Clinical Biomechanics. 1995;10(5):253-257. 40. McClay I, Manal K. Coupling parameters in runners with normal and excessive pronation. Journal of Applied Biomechanics. 1997;13(1):109-124. 41. Nigg BM, Cole GK, Nachbauer W. Effects of Arch Height of the Foot on Angular Motion of the Lower-Extremities in Running. Journal of Biomechanics. 1993;26(8):909916. 42. McLean SG, Lipfert SW, Van Den Bogert AJ. Effect of gender and defensive opponent on the biomechanics of sidestep cutting. Medicine and Science in Sports and Exercise. 2004;36(6):1008-1016. 43. Krosshaug T, Nakamae A, Boden B, et al. Estimating 3D joint kinematics from video sequences of running and cutting maneuvers -assessing the accuracy of simple visual inspection. Gait & Posture. 2007;26:378-385. 44. Uhorchak JM, Scoville CR, Williams GN, Arci ero RA, St Pierre P, Taylor DC. Risk factors associated with noncontac t injury of the anterior cr uciate ligament: A prospective four-year evaluation of 859 west point cadets (Vol 31, pg 831, 2003). American Journal of Sports Medicine. 2005;33(4):614-614. 45. Ostenberg A, Roos H. Injury risk factors in female European football. A prospective study of 123 players during one season. Scandinavian Journal of Medicine & Science in Sports. 2000;10(5):279-285. 46. Shambaugh JP, Klein A, Herbert JH. Structural Measures as Predictors of Injury in Basketball Players. Medicine and Science in Sports and Exercise. 1991;23(5):522-527. 47. Horton MG, Hall TL. Quadriceps Femoris Muscle Angle Normal Values and Relationships with Gender and Selected Skeletal Measures. Physical Therapy. 1989;69(11):897-901. 48. Guerra JP, Arnold MJ, Gajdosik RL. Q-A ngle Effects of Isometric Quadriceps Contraction and Body Position. Journal of Orthopaedic & Sports Physical Therapy. 1994;19(4):200-204.

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78 49. Huston LJ, Vibert B, Ashton-Miller JA, Wojtys EM. Gender differences in knee angle when landing from a drop-jump. Am J Knee Surg. 2001;14(4):215-219; discussion 219220. 50. Herrington L, Nester C. Q-angle undervalued? The relationship between Q-angle and medio-lateral position of the patella. Clinical Biomechanics. 2004;19(10):1070-1073. 51. Tillman MD, Bauer JA, Cauraugh JH, Trimble MH. Differences in lower extremity alignment between males and females Pote ntial predisposing fact ors for knee injury. Journal of Sports Medicine and Physical Fitness. 2005;45(3):355-359. 52. Moul JL. Differences in selected predictors of anterior cruciate ligament tears between male and female NCAA Division I collegiate basketball players. Journal of Athletic Training. 1998;33(2):118-121. 53. Myer GD, Ford KR, Hewett TE. The effects of gender on quadriceps muscle activation strategies during a maneuver that mimi cs a high ACL injury risk position. Journal of Electromyography and Kinesiology. 2005;15(2):181-189. 54. McLean SG, Walker KB, van den Bogert AJ. Effect of gender on lower extremity kinematics during rapid directi on changes: An integrated analysis of three sports movements. Journal of Science and Medicine in Sport. 2005;8(4):411-422. 55. Palmer I. On the injuries to the ligam ents of the knee join t: a clinical study. 1938. Clin Orthop Relat Res. 2007;454:17-22; discussion 14. 56. Anderson AF, Dome DC, Gautam S, Awh MH, Rennirt GW. Correlation of anthropometric measurements, strength, anterior cruciate ligament si ze, and intercondylar notch characteristics to sex differences in anterior cruciate ligament tear rates. American Journal of Sports Medicine. 2001;29(1):58-66. 57. Shelbourne KD, Davis TJ, Klootwyk TE. Th e relationship between intercondylar notch width of the femur and the incidence of anteri or cruciate ligament tears A prospective study. American Journal of Sports Medicine. 1998;26(3):402-408. 58. Souryal TO, Freeman TR, Daniel DM. Interc ondylar Notch Size and Anterior Cruciate Ligament Injuries in Athletes a Prospective-Study. American Journal of Sports Medicine. 1993;21(4):535-539. 59. Ireland ML, Ballantyne BT, Little K, McCl ay IS. A radiographic analysis of the relationship between the size a nd shape of the intercondylar no tch and anterior cruciate ligament injury. Knee Surgery Sports Traumatology Arthroscopy. 2001;9(4):200-205. 60. Fayad LM, Elan H. Rosenthal William B. Morrison John A. Carrino. Anterior cruciate ligament volume: Analysis of gender differences. Journal of Magnetic Resonance Imaging. 2008;27(1):218-223.

PAGE 79

79 61. Tillman MD, Smith KR, Bauer JA, Cauraugh JH, Falsetti AB, Pattishall JL. Differences in three intercondylar notch geometry indices between males and females: a cadaver study. Knee. 2002;9(1):41-46. 62. Soderman K, Alfredson H, Pietila T, Werner S. Risk factors for leg injuries in female soccer players: a prospective inve stigation during one out-door season. Knee Surgery Sports Traumatology Arthroscopy. 2001;9(5):313-321. 63. Nicholas JA. Injuries to Knee Ligaments Relationship to Loos eness and Tightness in Football Players. Journal of the American Medical Association. 1970;212(13):2236-&. 64. Kalenak A, Morehouse CA. Knee Stab ility and Knee Ligament Injuries. Jama-Journal of the American Medical Association. 1975;234(11):1143-1145. 65. Woodford-Rogers B, Cyphert L, Denegar CR. Risk factors for anteri or cruciate ligament injury in high school and college athletes. Journal of Athletic Training. 1994;29(4):343346. 66. Uhorchak JM, Scoville CR, Williams GN, Arci ero RA, St Pierre P, Taylor DC. Risk factors associated with noncontac t injury of the anterior cruc iate ligament A prospective four-year evaluation of 859 West Point cadets. American Journal of Sports Medicine. 2003;31(6):831-842. 67. Hsu WH, Fisk JA, Yamamoto Y, Debski RE, Woo SLY. Differences in torsional joint stiffness of the knee between genders A human cadaveric study. American Journal of Sports Medicine. 2006;34(5):765-770. 68. Wojtys EM A-MJ, Huston LJ. A gender-related difference in the contribution of the knee musculature to sagittal-plane shear stiffness in subjects with similar knee laxity. Journal of Bone and Joint Surgery. 2002;84:10-16. 69. Wojtys EM, Huston LJ, Schock HJ, Boylan JP Ashton-Miller JA. Gender differences in muscular protection of the knee in torsion in size-matched athletes. Journal of Bone and Joint Surgery-American Volume. 2003;85A(5):782-789. 70. Huston LJ, Wojtys EM. Neuromuscular performance characteristics in elite female athletes. American Journal of Sports Medicine. 1996;24(4):427-436. 71. Chandrashekar N, Mansouri H, Slauterbeck J, Hashemi J. Sex-based differences in the tensile properties of the huma n anterior cruciate ligament. Journal of Biomechanics. 2006;39(16):2943-2950. 72. Bates BT, Osternig LR, Mason B, James LS. Foot orthotic devices to modify selected aspects of lower extremity mechanics. Am J Sports Med. 1979;7(6):338-342. 73. Mueller MJ, Host JV, Norton BJ. Navicular Drop as a Composite Measure of Excessive Pronation. Journal of the American Podi atric Medical Association. 1993;83(4):198-202.

PAGE 80

80 74. Allen MK, Glasoe WM. Metrecom measurem ent of navicular drop in subjects with anterior cruciate ligament injury. Journal of Athletic Training. Oct-Dec 2000;35(4):403406. 75. Trimble MH, Bishop MD, Buckley BD, Fields LC, Rozea GD. The relationship between clinical measurements of lower extr emity posture and tibial translation. Clinical Biomechanics. 2002;17(4):286-290. 76. Jenkins WL, Killian CB, Williams DS, L oudon J, Raedeke SG. Anterior cruciate ligament injury in female and male athletes The relationship between foot structure and injury. Journal of the American Podiatric Medical Association. 2007;97:371-376. 77. Scranton PE, Whitesel JP, Powell JW, et al. A review of selected noncontact anterior cruciate ligament injuries in the National Football League. Foot & Ankle International. 1997;18(12):772-776. 78. Orchard J. Is there a relationship between ground and climatic conditions and injuries in football? Sports Medicine. 2002;32(7):419-432. 79. Orchard J, Seward H, McGivern J, Hood S. Rainfall, evaporation and the risk of noncontact anterior cruciate ligament injury in the Australian Football League. Medical Journal of Australia. 1999;170(7):304-306. 80. Backx FJG, Beijer HJM, Bol E, Erich WBM. Injuries in High-Risk Persons and HighRisk Sports a Longitudina l-Study of 1818 School-Children. American Journal of Sports Medicine. 1991;19(2):124-130. 81. Lambson RB, Barhnill BS, Higgins RW. Football cleat design and its effect on anterior cruciate ligament injuries A three-year prospective study. American Journal of Sports Medicine. 1996;24(2):155-159. 82. Ekstrand J, Timpka T, Hagglund M. Risk of in jury in elite football played on artificial turf versus natural grass: a prospective two-cohort study. British Journal of Sports Medicine. 2006;40(12):975-980. 83. Fuller CW, Dick RW, Corlette J, Schmalz R. Comparison of the incidence, nature and cause of injuries sustained on grass and new generation artific ial turf by male and female football players. Part 1: match injuries. British Journal of Sports Medicine. 2007;41:I20I26. 84. Steffen K, Andersen TE, Bahr R. Risk of injury on artificial turf and natural grass in young female football players. British Journal of Sports Medicine. 2007;41:I33-I37. 85. Milburn PD, Barry EB. Shoe-surface interact ion and the reduction of injury in rugby union. Sports Medicine. 1998;25(5):319-327.

PAGE 81

81 86. Girard O, Eicher F, Fourchet F, Micallef JP Millet GP. Effects of the playing surface on plantar pressures and potential injuries in tennis. British Journal of Sports Medicine. 2007;41. 87. Hawkins RD, Hulse MA, Wilkinson C, Hods on A, Gibson M. The association football medical research programme: an audit of injuries in professional football. British Journal of Sports Medicine. 2001;35(1):43-47. 88. Delee JC, Farney WC. Incidence of Injury in Texas High-School Football. American Journal of Sports Medicine. 1992;20(5):575-580. 89. Myklebust G, Maehlum S, Holm I, Bahr R. A prospective cohort study of anterior cruciate ligament injuries in elite Norwegian team handball. Scandinavian Journal of Medicine & Science in Sports. 1998;8(3):149-153. 90. Harmon KG, Ireland ML. Gender differences in noncontact anterior cruciate ligament injuries. Clinics in Sports Medicine. 2000;19(2):287-+. 91. Karageanes SJ, Blackburn K, Vangelos ZA. Th e association of the menstrual cycle with the laxity of the anterior cruciate ligament in adolescent female athletes. Clinical Journal of Sport Medicine. 2000;10(3):162-168. 92. Bani D. Relaxin: A pleiotropic hormone. General Pharmacology. 1997;28(1):13-22. 93. Shultz SJ, Kirk SE, Johnson ML, Sander TC, Perrin DH. Relationship between sex hormones and anterior knee laxity across the menstrual cycle. Medicine and Science in Sports and Exercise. 2004;36(7):1165-1174. 94. Heitz NA, Eisenman PA, Beck CL, Walker JA. Hormonal changes throughout the menstrual cycle and increased anterior cr uciate ligament laxity in females. Journal of Athletic Training. 1999;34(2):144-149. 95. Shultz SJ, Sander TC, Kirk SE, Perrin DH. Sex differences in knee joint laxity change across the female menstrual cycle. Journal of Sports Medicine and Physical Fitness. 2005;45(4):594-603. 96. Deie M, Sakamaki Y, Sumen Y, Urabe Y, Ikuta Y. Anterior knee laxity in young women varies with their menstrual cycle. International Orthopaedics. 2002;26(3):154-156. 97. Sarwar R, Niclos BB, Rutherford OM. Cha nges in muscle strength, relaxation rate and fatiguability during the human menstrual cycle. Journal of Physiology-London. 1996;493(1):267-272. 98. Lebrun CM. The Effect of the Phase of the Menstrual-Cycle and th e Birth-Control Pill on Athletic Performance. Clinics in Sports Medicine. 1994;13(2):419-441.

PAGE 82

82 99. Posthuma BW, Bass MJ, Bull SB, Nisker JA. Detecting Changes in Functional Ability in Women with Premenstrual-Syndrome. American Journal of Obstetrics and Gynecology. Feb 1987;156(2):275-278. 100. Slauterbeck JR FS, Smith MP, Clark RJ, Xu K, Starch DW, Hardy DM. The Menstrual Cycle, Sex Hormones, and Anterior Cruciate Ligament Injury. Journal of Athletic Training. 2002;37:275-278. 101. Fox S. Human Physiology. Boston: McGraw and Hill; 1999. 102. Liu SH, AlShaikh R, Panossian V, et al. Primary immunolocalization of estrogen and progesterone target cells in the hum an anterior cruciate ligament. Journal of Orthopaedic Research. 1996;14(4):526-533. 103. Sciore P, Frank CB, Hart DA. Identifica tion of sex hormone receptors in human and rabbit ligaments of the knee by reverse transc ription-polymerase chain reaction: Evidence that receptors are present in tissue from both male and female subjects. Journal of Orthopaedic Research. 1998;16(5):604-610. 104. Wojtys EM, Huston LJ. Neuromuscular Perfor mance in Normal and Anterior Cruciate Ligament-Deficient Lower-Extremities. American Journal of Sports Medicine. 1994;22(1):89-104. 105. Wojtys EM HL, Boynton MD, Spindler KP, Lindenfeld TN. The effect of the menstrual cycle on anterior cruciate ligament injuries in women as determined by hormone levels. American Journal of Sports Medicine. 2002;30(2):182-188. 106. Adachi N, Nawata K, Maeta M, Kurozawa Y. Relationship of the menstrual cycle phase to anterior cruciate ligament injuries in teenaged female athletes. Archives of Orthopaedic and Trauma Surgery. May 2008;128(5):473-478. 107. Shirtcliff EA, Granger DA, Schwartz EB, Curran MJ, Booth A, Overman WH. Assessing estradiol in biobehavioral st udies using saliva and blood s pots: Simple radioimmunoassay protocols, reliability, and comparative validity. Hormones and Behavior. 2000;38(2):137147. 108. Baker FC, Driver HS. Circadian rhyt hms, sleep, and the menstrual cycle. Sleep Medicine. 2007;8:613-622. 109. Moller Nielsen JH, M. Sports injuries and oral contraceptives use. Is there a relationship? Sports Medicine. 1991;12(3):152-160. 110. Hewett TE, Stroupe AL, Nance TA, Noyes FR. Plyometric training in female athletes Decreased impact forces and increased hamstring torques. American Journal of Sports Medicine. 1996;24(6):765-773.

PAGE 83

83 111. Ford KR, Myer GD, Hewett TE. Valgus knee motion during landing in high school female and male basketball players. Medicine and Science in Sports and Exercise. 2003;35(10):1745-1750. 112. Knapik JJ, Bauman CL, Jones BH, Harris JM, Vaughan L. Preseason Strength and Flexibility Imbalances Associated with Athletic Injuries in Female Collegiate Athletes. American Journal of Sports Medicine. 1991;19(1):76-81. 113. Li G, Rudy TW, Sakane M, Kanamori A, Ma CB, Woo SLY. The importance of quadriceps and hamstring muscle loading on knee kinematics land in-situ forces in the ACL. Journal of Biomechanics. 1999;32(4):395-400. 114. Torzilli PA, Deng XH, Ramcharan M. Effect of compressive strain on cell viability in statically loaded articular cartilage. Biomechanics and Modeling in Mechanobiology. 2006;5(2-3):123-132. 115. Beynnon BD, Johnson RJ, Fleming BC, Stankewi ch CJ, Renstrom PA, Nichols CE. The strain behavior of the anterior cruciate ligament during squatting and active flexionextension A comparison of an open and a closed kinetic chain. American Journal of Sports Medicine. 1997;25(6):823-829. 116. Pandy MG, Shelburne KB. Dependence of cruc iate-ligament loading on muscle forces and external load. Journal of Biomechanics. 1997;30(10):1015-1024. 117. Urabe Y, Kobayashi R, Sumida S, et al. Electromyographic analys is of the knee during jump landing in male and female athletes. Knee. 2005;12(2):129-134. 118. Barrett GR, Field LD. Comparison of Pa tella Tendon Versus Patella Tendon Kennedy Ligament Augmentation Device for Anterior Cruciate Ligament Reconstruction Study of Results, Morbidity, and Complications. Arthroscopy. 1993;9(6):624-632. 119. Woo SLY, Hollis JM, Adams DJ, Lyon RM, Ta kai S. Tensile Properties of the Human Femur-Anterior Cruciate Ligament-Tibia Co mplex the Effects of Specimen Age and Orientation. American Journal of Sports Medicine. 1991;19(3):217-225. 120. Ebstrup JF, Bojsen-Moller F. Anterior cruc iate ligament injury in indoor ball games. Scandinavian Journal of Medici ne & Science in Sports. 2000;10(2):114-116. 121. Malinzak RA, Colby SM, Kirkendall DT, Yu B, Garrett WE. A comparison of knee joint motion patterns between men and wome n in selected athletic tasks. Clinical Biomechanics. 2001;16(5):438-445. 122. Sigward SM, Powers CM. The influence of gender on knee kinematics, kinetics and muscle activation patterns during side-step cutting. Clinical Biomechanics. 2006;21(1):41-48.

PAGE 84

84 123. Lephart SM, Ferris, C. M., Riem ann, B. L., Myers, J. B., Fu, F. H. Gender differences in strength and lower extremity kinematics during landing. Clinical Orthopaedics and Related Research. 2002;401:162-169. 124. Hewett TE, Lindenfeld TN, Riccobene JV, Noyes FR. The effect of neuromuscular training on the incidence of knee injury in female athletes A prospective study. American Journal of Sports Medicine. 1999;27(6):699-706. 125. Wojtys EM, Huston LJ, Lindenfeld TN, Hewe tt TE, Greenfield M. Association between the menstrual cycle and anterior cruciate ligament injuries in female athletes. American Journal of Sports Medicine. 1998;26(5):614-619. 126. Fleming BC, Renstrom PA, Be ynnon BD, et al. The effect of weightbearing and external loading on anterior cruciate ligament strain. Journal of Biomechanics. 2001;34(2):163170. 127. O'Connor JJ. Can muscle co-contraction protec t the knee ligaments after injury or repair? Journal of Bone and Joint Surgery. 1993;75:41-48. 128. Dufek JS, Bates BT. Biomechanical Factors Associated with Injury During Landing in Jump Sports. Sports Medicine. 1991;12(5):326-337. 129. Cerulli G, Benoit DL, Lamontagne M, Caraffa A, Liti A. In vivo anterior cruciate ligament strain behaviour during a rapid deceleration movement: case report. Knee Surgery Sports Traumatology Arthroscopy. 2003;11(5):307-311. 130. Yu B, McClure SB, Onate JA, Guskiewi cz KM, Kirkendall DT, Garrett WE. Age and gender effects on lower extremity kinematics of youth soccer players in a stop-jump task. American Journal of Sports Medicine. 2005;33(9):1356-1364. 131. Chappell JD, Herman DC, Knight BS, Kirke ndall DT, Garrett WE, Yu B. Effect of fatigue on knee kinetics and kine matics in stop-jump tasks. American Journal of Sports Medicine. 2005;33(7):1022-1029. 132. Salci Y, Kentel BB, Heycan C, Akin S, Korkusuz F. Comparison of landing maneuvers between male and female college volleyball players. Clinical Biomechanics. 2004;19(6):622-628. 133. Kernozek TW, Torry MR, Van Hoof H, Cowley H, Tanner S. Gender differences in frontal and sagittal plane biomechanics during drop landings. Medicine and Science in Sports and Exercise. 2005;37(6):1003-1012. 134. Ford KR, Myer GD, Smith RL, Vianello RM, Seiwert SL, Hewett TE. A comparison of dynamic coronal plane excursion between ma tched male and female athletes when performing single leg landings. Clinical Biomechanics. 2006;21(1):33-40. 135. Andrews JR, Axe MJ. The Classifica tion of Knee Ligament Instability. Orthopedic Clinics of North America. 1985;16(1):69-82.

PAGE 85

85 136. Dugan SA, Bhat KP. Biomechanic s and analysis of running gait. Physical Medicine and Rehabilitation Clinics of North America. 2005;16:603-621. 137. Chappell JD, Yu B, Kirkendall DT, Garrett WE. A comparison of knee kinetics between male and female recreational at hletes in stop-jump tasks. American Journal of Sports Medicine. 2002;30:261-267. 138. Bendjaballah MZ, ShiraziAdl A, Zukor DJ. Fi nite element analysis of human knee joint in varus-valgus. Clinical Biomechanics. 1997;12(3):139-148. 139. Fagenbaum R, Darling WG. Jump landing strategies in male and female college athletes and the implications of such strategies for anterior cruciate ligament injury. American Journal of Sports Medicine. 2003;31(2):233-240. 140. Ford KR, Myer GD, Smith RL, Byrnes RN, Dopirak SE, Hewett TE. Use of an overhead goal alters vertical jump performance and biomechanics. Journal of Strength and Conditioning Research. 2005;19(2):394-399. 141. Zeller BL, McCrory JL, Ben Kibler W, Uhl TL. Differences in kinematics and electromyographic activity between men a nd women during the single-legged squat. American Journal of Sports Medicine. 2003;31(3):449-456. 142. Decker MJ, Torry MR, Wyland DJ, Stere tt WI, Steadman JR. Gender differences in lower extremity kinematics, kinetics and energy absorption during landing. Clinical Biomechanics. 2003;18(7):662-669. 143. Landry SC, McKean KA, Hubley-Kozey CL, Stanish WD, Deluzio KJ. Unanticipated running and cross cutting maneuvers demonstrate neuromuscular and lower limb, biomechanical differences between elite adol escent male and female soccer players. Journal of Biomechanics. 2007;40(Supplement 2):S379-S379. 144. Sanna G, O'Connor KM. Fatigue-related change s in stance leg mechan ics during sidestep cutting maneuvers. Clinical Biomechanics. 2008;23(7):946-954. 145. Pollard CD, Sigward SM, Powers CM. Gender differences in hip joint kinematics and kinetics during side-step cutting maneuver. Clinical Journal of Sport Medicine. 2007;17(1):38-42. 146. Hanson AM, Padua DA, Blackburn JT, Prentic e WE, Hirth CJ. Musc le activation during side-step cutting maneuvers in male and female soccer athletes. Journal of Athletic Training. 2008;43(2):133-143. 147. Garrison JC, Hart JM, Palmieri RM, Kerri gan DC, Ingersoll CD. Lower extremity EMG in male and female college soccer players during single-leg landing. Journal of Sport and Rehabilitation. 2005;14:48-57. 148. Ferber R, Davis IM, Williams DS. Gender differences in lower extremity mechanics during running. Clinical Biomechanics. 2003;18(4):350-357.

PAGE 86

86 149. Chumanov ES, Wall-Schefer C, Heidersche it BC. Gender differences in walking and running on level and inclined surfaces. Clinical Biomechanics. 2008;23(10):1260-1268. 150. Sigward SM, Powers CM. Loading characteris tics of females exhibiting excessive valgus moments during cutting. Clinical Biomechanics. 2007;22(7):827-833. 151. Pollard CD, Davis IM, Hamill J. Influence of gender on hip and knee mechanics during a randomly cued cutting maneuver. Clinical Biomechanics. 2004;19(10):1022-1031. 152. Michaud PA, Renaud A, Narring F. Sports activ ities related to injuries? A survey among 9-19 year olds in Switzerland. Injury prevention : journal of the International Society for Child and Adolescent Injury Prevention. 2001;7:41-45. 153. Hewett TE, Myer GD, Ford KR. Decrease in neuromuscular control about the knee with maturation in female athletes. Journal of Bone and Joint Surgery-American Volume. 2004;86A(8):1601-1608. 154. Hewett TE, Ford KR, Myer GD, Wanstrath K, Scheper M. Gender differences in hip adduction motion and torque during a single-leg agility maneuver. Journal of Orthopaedic Research. 2006;24(3):416-421. 155. Quatman CE, Ford KR, Myer GD, Hewett TE. Maturation leads to gender differences in landing force and vertical jump performance A longitudinal study. American Journal of Sports Medicine. 2006;34(5):806-813. 156. Hass CJ, Schick EA, Chow JW, Tillman MD, Brunt D, Cauraugh JH. Lower extremity biomechanics differ in prepubescent and post pubescent female athletes during stride jump landings. Journal of Applied Biomechanics. 2003;19(2):139-152. 157. Mandelbaum BR, Silvers HJ, Watanabe DS, et al. Effectiveness of a neuromuscular and proprioceptive training program in preventing anterior cruciate ligament injuries in female athletes 2-year follow-up. American Journal of Sports Medicine. 2005;33(7):1003-1010. 158. Gilchrist J, Mandelbaum BR, Melancon H, et al. A randomized controll ed trial to prevent noncontact anterior Cruciate ligament injury in female collegiate soccer players. American Journal of Sports Medicine. 2008;36(8):1476-1483. 159. Myer GD, Ford KR, Palumbo JP, Hewe tt TE. Neuromuscular training improves performance and lower-extremity biomechanics in female athletes. Journal of Strength and Conditioning Research. 2005;19(1):51-60. 160. Pollard CD, Sigward SM, Ota S, Langford K, Powers CM. The influence of in-season injury prevention training on lower-extremity kinematics during landing in female soccer players. Clinical Journal of Sport Medicine. 2006;16(3):223-227.

PAGE 87

87 161. Chappell JD, Limpisvasti O. Effect of a ne uromuscular training pr ogram on the kinetics and kinematics of jumping tasks. American Journal of Sports Medicine. 2008;36(6):1081-1086. 162. Kato S, Urabe Y, Kawamura K. Alignmen t control exercise changes lower extremity movement during stop movements in female basketball players. Knee. 2008;15(4):299304. 163. Herman DC, Weinhold PS, Guskiewicz KM, Ga rrett WE, Yu B, Padua DA. The effects of strength training on the lower extremity biomechanics of female recreational athletes during a stop-jump task. American Journal of Sports Medicine. 2008;36(4):733-740. 164. Zebis MK, Bencke J, Andersen LL, et al. The effects of neuromus cular training on knee joint motor control during si decutting in female elite soccer and handball players. Clinical Journal of Sport Medicine. 2008;18(4):329-337. 165. Petersen W, Braun C, Bock W, et al. A controlled prospective case control study of a prevention training program in female team handball players: the German experience. Archives of Orthopae dic and Trauma Surgery. 2005;125(9):614-621. 166. Heidt RS, Sweeterman LM, Carlonas RL, Traub JA, Tekulve FX. Avoidance of soccer injuries with preseason conditioning. American Journal of Sports Medicine. 2000;28(5):659-662. 167. Kraemer WJ, Keuning M, Ratamess NA, et al Resistance training combined with benchstep aerobics enhances women's health profile. Medicine and Science in Sports and Exercise. 2001;33(2):259-269. 168. Grindstaff TL, Hammill RR, Tuzson AE, Hert el J. Neuromuscular control training programs and noncontact anterior cruciate ligament injury rates in female athletes: A numbers-needed-to-treat analysis. Journal of Athletic Training. 2006;41(4):450-456. 169. Gandevia SC. Spinal and supraspina l factors in human muscle fatigue. Physiological Reviews. 2001;81(4):1725-1789. 170. Wojtys EM, Wylie BB, Huston LJ. The eff ects of muscle fatigue on neuromuscular function and anterior tibial tr anslation in healthy knees. American Journal of Sports Medicine. 1996;24(5):615-621. 171. Nyland JA, Caborn DN, Shapiro R, Johnson DL. Fatigue after eccentric quadriceps femoris work produces earlier gastrocnemiu s and delayed quadriceps femoris activation during crossover cutting among normal athletic women. Knee Surg Sports Traumatol Arthrosc. 1997;5(3):162-167. 172. Rozzi SL, Lephart SM, Fu FH. Effects of muscular fatigue on knee joint laxity and neuromuscular characteristics of male and female athletes. Journal of Athletic Training. 1999;34(2):106-114.

PAGE 88

88 173. Mercer TH, Gleeson NP, Wren K. Influence of prolonged intermittent high-intensity exercise on knee flexor strength in male and female soccer players. European Journal of Applied Physiology. 2003;89(5):506-508. 174. Borotikar BS, Newcomer R, Koppes R, McLean SG. Combined effects of fatigue and decision making on female lower limb la nding postures: Central and peripheral contributions to ACL injury risk. Clinical Biomechanics. 2008;23(1):81-92. 175. Orlshimo KF, Kremenic IJ. Effect of fa tigue on single-leg hop landing biomechanics. Journal of Applied Biomechanics. 2006;22(4):245-254. 176. Madigan ML, Pidcoe PE. Changes in la nding biomechanics duri ng a fatiguing landing activity. Journal of Electromyography and Kinesiology. 2003;13(5):491-498. 177. Rahnama N, Reilly T, Lees A, Graham-Smith P. Muscle fatigue induced by exercise simulating the work rate of competitive soccer. Journal of Sports Sciences. 2003;21(11):933-942. 178. Lepers R, Hausswirth C, Maffiuletti N, Brisswalter J, van Hoecke J. Evidence of neuromuscular fatigue after prolonged cycling exercise. Medicine and Science in Sports and Exercise. 2000;32(11):1880-1886. 179. Kernozek TW, Torry MR, Iwasaki M. Gender differences in lower extremity landing mechanics caused by neuromuscular fatigue. American Journal of Sports Medicine. 2008;36(3):554-565. 180. McLean SG. The ACL injury enigma: We can't prevent what we don't understand. Journal of Athletic Training. 2008;43(5):538-540. 181. Andrews JR, McLeod WD, Ward T, Ho ward K. The cutting mechanism. American Journal of Sports Medicine. 1977;5(3):111-121. 182. James CR, Sizer PS, Starch DW, Lockhart TE, Slauterbeck J. Gender differences among sagittal plane knee kinematic and ground r eaction force characteristics during a rapid sprint and cut maneuver. Research Quarterly fo r Exercise and Sport. 2004;75(1):31-38. 183. McLean SG, Huang X, van den Bogert AJ. Association between lower extremity posture at contact and peak knee valgus moment during sidestepping: Implications for ACL injury. Clinical Biomechanics. 2005;20(8):863-870. 184. Besier TF, Lloyd DG, Ackland TR, Cochrane JL. Anticipatory effects on knee joint loading during running and cutting maneuvers. Medicine and Science in Sports and Exercise. 2001;33(7):1176-1181. 185. McLean SG, Myers PT, Neal RJ, Walters MR. A quantitative analysis of knee joint kinematics during the sidestep cutting maneuve r. Implications for non-contact anterior cruciate ligament injury. Bull Hosp Jt Dis. 1998;57(1):30-38.

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89 186. Houck JR, Duncan A, DeHaven KE. Comparison of frontal plane trunk kinematics and hip and knee moments during anticipated and una nticipated walking a nd side step cutting tasks. Gait & Posture. 2005;24(3):314-322. 187. Sell TC, Ferris CM, Abt JP, et al. Predictors of proximal tibia anterior shear force during a vertical stop-jump. Journal of Orthopaedic Research. 2007;25:1589-1597. 188. Cowling EJ, Steele JR, McNair PJ. Effect of verbal instructions on muscle activity and risk of injury to the anterior cruciate ligament during landing. British Journal of Sports Medicine. 2003;37(2):126-130. 189. Hutchinson MR, Ireland ML. Knee Injuries in Female Athletes. Sports Medicine. 1995;19(4):288-302. 190. Borowski LA, Yard EE, Fields SK, Comsto ck RD. The epidemiology of US high school basketball injuries, 2005-2007. American Journal of Sports Medicine. 2008;36(12):23282335. 191. McLean SG, Neal RJ, Myers PT, Walters MR Knee joint kinematics during the sidestep cutting maneuver: potential for injury in women. Medicine and Science in Sports and Exercise. 1999;31(7):959-968. 192. Griffin LY, Albohm MJ, Are ndt EA, et al. Understandi ng and preventing noncontact anterior cruciate ligament injuries A review of the Hunt Valley II Meeting, January 2005. American Journal of Sports Medicine. 2006;34:1512-1532. 193. O'Connor KM, Monteiro SK, Hoelker IA. Comparison of Selected Lateral Cutting Activities Used to Assess ACL Injury Risk. Journal of Applied Biomechanics. 2009;25(1):9-21. 194. Brown TN, Palmieri-Smith RM, McLean SG Differences between Sexes and Limbs in Hip and Knee Kinematics and Kinetics duri ng Anticipated and Unanticipated Jump Landings: Implications for ACL injury. British Journal of Sports Medicine. 2009;Epub ahead of print. 195. Padua DA, Carcia CR, Arnold BL, Granata KP Gender differences in leg stiffness and stiffness recruitment strategy during two-legged hopping. Journal of Motor Behavior. 2005;37(2):111-125. 196. Pollard CD, Heiderscheit BC, van Emmerik REA, Hamill J. Gender differences in lower extremity coupling variability during an unanticipated cutting maneuver. Journal of Applied Biomechanics. 2005;21(2):143-152. 197. Rand MK, Ohtsuki T. EMG analysis of lower limb muscles in humans during quick change in running directions. Gait & Posture. 2000;12(2):169-183. 198. Novacheck TF. The biomechanics of running. Gait & Posture. 1998;7:77-98.

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90 199. Patla AE, Adkin A, Ballard T. Online stee ring coordinatino and c ontrol of body center of mass, head and body reorientation. Experimental Br ain Research. 1999;129(4):629-634. 200. Winter D. Anatomy, biomechanics, and cont rol of balance during standing and walking. Gait & Posture. 1995;3:193-214.

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91 BIOGRAPHICAL SKETCH Ryan Ashley Mize ll was born in Georgia to Dr. Russ Mizell III, a professor of entomology, and Patricia Mizell, a teacher. The family moved to Monticello, Florida, where he resided until moving to Gainesville to attend the University of Fl orida. Ryan graduated with a bachelors degree in exercise and sport science. He attended graduate school and attained a masters degree in biomechanics in 2009. Ryan has an older brother, Rusty, who attended the University of Florida and now lives in Tampa with his wife and son.