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Methodological Report: Dynamic Field Tests Used in an NFL Combine Setting to Identify Lower-Extremity Functional Asymmetries

Hickey, Kathryn C1,2; Quatman, Carmen E1,3; Myer, Gregory D1,4; Ford, Kevin R1,5; Brosky, Joseph A2; Hewett, Timothy E1,5

Journal of Strength and Conditioning Research: December 2009 - Volume 23 - Issue 9 - p 2500-2506
doi: 10.1519/JSC.0b013e3181b1f77b
Original Research
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Hickey, KC, Quatman, CE, Myer, GD, Ford, KR, Brosky, JA, and Hewett, TE. Methodological report: dynamic field tests used in an NFL combine setting to identify lower-extremity functional aysmmetries. J Strength Cond Res 23(9): 2500-2506, 2009-Side-to-side differences in lower-extremity biomechanics may be predictive of increased risk of lower-extremity injuries in athletes. The purpose of this report is to provide field testing methodology for tests designed to isolate lower-extremity asymmetry and to demonstrate the potential for these tests to provide reliable measures. Six athletes (3 females, 3 males) were tested on 2 consecutive days for activities incorporated into a replicated National Football League (NFL) combine setting. Vertical hop power (VHP) and jump height were measured on a portable force platform as athletes performed maximum effort hops for 10 seconds. The modified agility T-test (MAT) incorporates two 90-degree single-leg cuts during the trial and was measured as total time for completion. Intraclass correlations (within ICC [3,k], between ICC [3,1]) were calculated. The VHP test had good to excellent within-session reliability for peak power of both the right (ICC = 0.942) and left (ICC = 0.895) sides. Jump height showed excellent within-session reliability for both the right (ICC = 0.963) and left (ICC = 0.940) sides. The between-session reliability for peak power between jumps was good for the right (ICC = 0.748) and left (ICC = 0.834) sides. Jump height showed good to excellent between-session reliability on the right (ICC = 0.794) and left (ICC = 0.909) sides. The MAT also showed good reliability between days (ICC = 0.825).The results indicate that the VHP test provides reliable assessment of both within- and between-session jump height and power production. The MAT also provides good reliability between testing days. Both the VHP and the MAT may be useful for clinicians to identify the presence of lower-limb asymmetry and potential injury risk factors in athletic populations.

1Cincinnati Children's Hospital Research Foundation Sports Medicine Biodynamics Center and Human Performance Laboratory, Cincinnati, Ohio; 2Lansing School of Nursing and Health Sciences at Bellarmine University, Doctor of Physical Therapy Program, Louisville, Kentucky; 3Engineering Center for Orthopaedic Research Excellence, University of Toledo, Toledo, Ohio; 4Rocky Mountain University of Health Professions, Provo, Utah; and 5The University of Cincinnati College of Medicine, Departments of Pediatrics, Orthopaedic Surgery and Departments of Biomedical Engineering and Rehabilitation Sciences, Cincinnati, Ohio

Address correspondence to Gregory D. Myer, greg.myer@cchmc.org.

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Introduction

Presently, more than 7 million athletes participate in organized high school varsity sports (31). An estimated 380,000 athletes participate in intercollegiate sports, and millions of other athletes of all age levels are participating recreationally (1). With such a large number of children, adolescents, and adults participating in a wide variety of physically demanding activities, sports injuries are a major concern among athletes, athletic organizations, and health care providers. Appropriate diagnosis and treatment following injury are essential to return an athlete quickly and safely to sports. However, before an athlete returns, it is important to determine their level of readiness to meet the functional demands of the sport with minimal risk of reinjury or compensatory injury (29).

The majority of sports injuries occur in the lower extremities (8,10,11,17), usually during jumping and cutting maneuvers (4,10,26,27,33). Lower-extremity asymmetries in strength or functional abilities may be related to an increased risk for lower-extremity injury in athletic populations (15,20,29,32). If these asymmetries in side-to-side mechanics of running, cutting, jumping, and landing persist after rehabilitation from a lower-extremity injury, the athlete's risk for injury may be increased for both the rehabilitated and contralateral limb (3,21,36,40). Diagnostic tests that can be used to identify side-to-side functional differences may be useful for the determination of an athlete's readiness to safely return to sports following a lower-extremity injury (28,29,36). Moreover, functional performance tests that measure lower-extremity asymmetry may help identify healthy athletes who are at increased risk for lower-extremity injury (15,20,32).

Many current functional assessment tests rely on subjective visual evaluations for a general analysis of movement. However, functional tests for evaluation of an athlete's ability to safely participate in sports should include objective, valid, reliable measurements of sports-specific movements (6,9,16,28,29,36). Tests that measure dynamic tasks during cutting and jumping activities are important to assess power, strength, landing kinetics, and coordination during high-risk activities (29). However, a test that objectively measures single-leg hop power or the difference between single-limb cutting maneuvers was not found in the published literature. Reliable, objective, sports-related functional assessment tools must be developed and utilized for the evaluation of the effectiveness and progression of rehabilitation protocols, determination of readiness to return to sport (28,29), and identification of athletes who may be at increased risk for injury (15,16). The purpose of this report is to provide field testing methodology designed to isolate lower-extremity asymmetry and to demonstrate the potential for these tests to provide reliable measures.

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Methods

Experimental Approach to the Problem

The current methodological report provides an approach to apply objective field testing methodology with functional tests designed to isolate lower-extremity asymmetry and to demonstrate the potential for these tests to provide reliable measures. These data were collected in a large-scale 2-day field setting designed to replicate National Football League (NFL) combine testing procedures. Quantitative measurements, such as the described functional assessment, can be beneficial to identify preseason asymmetries that may be predictive of injury or reinjury risk in athletes (14).

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Subjects

Six athletes (3 males, 3 females) were tested on 2 consecutive days. Informed written consent was obtained from subjects and approved by the Institutional Review Board. After the informed consent was obtained, height and weight were measured and recorded. A questionnaire was utilized to determine prior history of knee injury. Two of the female subjects had anterior cruciate ligament (ACL) reconstructions at least 2 years prior to testing; 1 subject had a unilateral ACL reconstruction, and the other had bilateral ACL reconstructions. Subjects reported recreational involvement in basketball, football, running, and/or hockey. No subjects reported any current injuries and all were currently out of season for their preferred sporting activities.

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Procedures

Subjects performed 2 functional tasks (vertical hop power [VHP] and modified agility T-test [MAT] tests) in a local high school gymnasium. Before testing, all subjects were instructed how to perform the 2 tests, followed by a demonstration by the same researcher. If a task was not performed according to instructions or data were unable to be recorded, the subject immediately stopped and rested and the test was repeated. After the test, subjects were given 2 minutes to recover. This recovery was given between VHP jumping sets and MAT runs and when transferring between tests.

The VHP test was measured on a portable force platform (Figure 1; Accupower AMTI, Watertown, Massachusetts, U.S.A.) and recorded with AccuPower Software (Frappier Acceleration, Fargo, North Dakota, U.S.A.). Subjects were instructed to repeatedly hop on 1 leg “as high as possible while remaining under control” for 10 seconds (Figure 2). The start leg was determined by random selection and the subject balanced on the leg until the subjects were given a cue by the investigator to begin the hopping task. The jump time, force upon landing, and power during takeoff were measured and recorded during each 10-second VHP test. If a subject did not fully contact the force plate, the trial was terminated and the test was repeated. After the subject completed testing on 1 leg, the test was then repeated on the opposite leg.

Figure 1

Figure 1

Figure 2

Figure 2

The MAT test (Figure 3) was developed from the standard T-test (Figure 4) to evaluate lower-extremity side-to-side differences in cutting and running maneuvers. The T-test is a timed performance test frequently utilized for sports that require quick starts, dynamic changes in direction, and efficient movement. However, the standard agility T-test combines left and right directional changes. Although this is functionally ideal for individuals who require cutting from both sides, it is not useful to evaluate and compare a potential unilateral deficit. Therefore, we modified the agility T-test to include cuts and shuffles to only 1 side (29). The start leg for the MAT test was randomly assigned. The subject was initially guided through the course by the primary investigator, emphasizing the importance of performing a shuffling movement and not running or using crossover steps during the lateral movement portions of the test. The subjects informed the investigator when they were ready to begin the test. All trials were electronically timed with a stopwatch. After the subjects felt they had an adequate rest (approximately 2 minutes), the other direction was tested. The total time was recorded for each leg. Only 1 trial was performed per leg.

Figure 3

Figure 3

Figure 4

Figure 4

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Statistical Analyses

The VHP and MAT tests were performed within the 2 testing days, evaluating the left and right sides separately. Additionally, the VHP was compared between sessions. Because fatigue would likely affect the results of multiple trials of the VHP test, intrasession results were calculated between 3 of the jumps performed in 1 trial. For both the power and jump height of the VHP test, the first 3 consecutive hops that reached at least 70% of the jump height of the initial jump were evaluated for reliability. For intersession results, the first 3 consecutive hops that reached at least 70% of the initial jump of the first day were compared to the first 3 jumps that met the same criteria on the second day. Means and standard deviations were calculated from the data collected for each test and intraclass correlation coefficients (within ICC [3,k], between ICC [3,1]) were calculated with statistical software. ICC values less than 0.4 were reported as poor, from 0.4 to 0.75 were fair to good, and greater than 0.75 were considered excellent (38).

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Results

The mean age of the subjects was 20.8 ± 3.8 years. The subjects weighed 68.9 ± 43.3 kg and measured 172.21 ± 9.12 cm in height. The mean power measured during the VHP test was 28.05 ± 3.58 W in this population. The mean jump height measured during the VHP test was 13.06 ± 3.04 cm (Table 1). Separately, the left mean power was 28.47 ± 3.75 W and the right was 27.62 ± 3.40 W. The left mean jump height was 13.08 ± 2.88 cm and the right was 13.04 ± 3.23 cm.

Table 1

Table 1

The VHP test had excellent within-session reliability for peak power of both the right (ICC = 0.942) and left (ICC = 0.895) sides. Jump height showed excellent within-session reliability for both the right (ICC = 0.963) and left (ICC = 0.940) sides.

The between-session reliability for peak power between jumps was good for the right (ICC = 0.748) and left (ICC = 0.834) sides. Jump height showed excellent between-session reliability on the right (ICC = 0.794) and left (ICC = 0.909) sides.

The mean time to complete the MAT test in this population was 9.59 ± 0.57 seconds. The subjects performed the right MAT test in a mean time of 9.55 ± 0.57 seconds and the left MAT test in a mean of 9.63 ± 0.59 seconds. The MAT test also showed excellent reliability between days (ICC = 0.825).

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Discussion

The purpose of this report is to provide objective field-testing methodology designed to isolate lower-extremity asymmetry and to demonstrate the potential for these tests to provide reliable measures. Quantitative measurements, such as functional assessment tests, can be used to document the progression of a patient's strength, tolerance, and performance abilities during rehabilitation (5,29,32,36). Highly reliable functional assessment tests are required to compare results from multiple testing sessions during the progression of rehabilitation protocols. The current findings indicate that the VHP and MAT tests provide good to excellent reliability as lower-extremity functional assessment tests. One major hypothesis was accepted because the VHP and the MAT tests provide high within-session, but not between-session, test-retest reliability (ICC > 0.75) in athletes tested. These tests may be useful measures of determining an athlete's readiness to return to sport following lower-extremity injury.

Athletes who have experienced a significant lower-extremity injury such as an ACL rupture are likely at an increased risk of injury for both the injured and contralateral limbs (2,34,39,40). Paterno et al. demonstrated that female athletes who have completed rehabilitation and returned to sports following ACL reconstruction continued to have significant asymmetries in landing, cutting, and jumping more than 2 years after surgery (36). Mattacola et al. and Kobayashi et al. found that significant asymmetry in strength measures were present 18 months after ACL reconstruction (22,25). Because side-to-side asymmetries may increase risk for injury in healthy subjects (15), residual side-to-side deficits may be important risk factors to consider before allowing an athlete to return to sports activities and should be targeted during the rehabilitation process (22,25,29,36). Functional assessment tests may help identify deficits in strength, coordination, landing kinetics, and power that may increase an athlete's risk of injury when returning to sports activities (5,19,22,25,29,32,36).

Current functional assessment tests, such as performance during shuttle run tests and force measurements during landing from a jump or side-step tasks may not effectively evaluate movement performance or contributions of a single limb (6,16,18,19,29,35). Functional hop tests such as the single-leg hop, crossover hop, triple hop, and timed hop have been used to evaluate ACL injury rehabilitation progress (32). However, many of these functional hop tests have a low sensitivity and specificity for determining lower-extremity asymmetries (16), and these movements do not take into account other high-risk multi-planar movements, such as perpendicular cutting and challenging lateral motions (7,29). Thus, additional tests may be required to further evaluate the functional readiness of an athlete to return to sport following ACL reconstruction or other lower-extremity injury.

The VHP and MAT tests used in this study may provide alternative methods to evaluate lower-extremity symmetry during functionally demanding tasks. In the past, power hops on a force plate and functional hop tests for subjective analysis of lower-extremity function have been used to evaluate single-limb symmetry (29,32). However, in sporting activities, athletes must make multiple single-footed ground contacts safely, while controlling the landing forces and takeoff power. Therefore, a VHP test was developed to integrate these parameters into a functional assessment test. At the same time, the MAT test was developed to evaluate perpendicular cutting tasks. Pauole et al. reported that the T-test (Figure 4), typically used in football conditioning, is a useful tool for determining sports-related measures of speed, power, and agility (37). The T-test incorporates perpendicular cuts in both right and left directions during the timed test. To identify limb function asymmetries, the T-test was modified to isolate right and left directional cuts into 2 different test measures (Figure 3).

Both the VHP and MAT tests are challenging tasks that require sufficient strength and neuromuscular control. Although these tests may be excellent tools for evaluating patient progress following injury and readiness to return to sport, using a single test in isolation may not adequately simulate all of the challenging movements an athlete may encounter on the playing field. Thus, incorporation of several different types of functional assessment tests are important when evaluating an athlete's readiness to return to sport (29).

Clinicians should be especially aware of the possible gap between an athlete's perceived vs. actual functional readiness to return to sport (29). Objective, quantitative functional assessment tests, such as the VHP and MAT, may help clinicians justify why sports restriction may be important, despite an athlete's perceived readiness to return to sport. At the same time, fear of reinjury is a major concern of many athletes and their fear may hinder performance and return to sports activity (23). Kvist and colleagues reported that 24% of athletes who sustained ACL injury did not return to their pre-injury level of activity because of fear of reinjury (23). Functional assessment tests may help athletes gain confidence in their rehabilitated limbs because quantitative measures allow the athlete to see progressive improvement during the rehabilitation process and show the athlete that they are within sufficient ranges of function compared to their noninjured limb before returning to sport.

Functional assessment tests may also be useful as pre-screening tools to identify risks for lower-extremity injury, particularly tools that identify lower-extremity asymmetry. Hewett and colleagues prospectively measured biomechanical factors predictive of ACL injury in healthy female athletes (15). Uninjured athletes who later sustained an ACL injury after biomechanical testing demonstrated significant side-to-side differences in knee load compared to control athletes. Side-to-side knee abduction movement was 6.4 times greater in athletes who sustained ACL injury compared to control athletes. In addition, knee abduction movements predicted ACL injury with high sensitivity and specificity (15). If effective screening tools can be developed to identify athletes at risk for potential lower-extremity injury, these at-risk athletes can be placed in injury prevention programs (12,13,24,30).

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Practical Applications

Functional assessment tests that measure functional ability provide clinicians with useful tools to monitor the rehabilitation progress of athletes. The VHP test and the MAT tests are objective, quantitative, and reliable functional field assessment tests that may help clinicians evaluate patient rehabilitation progress and readiness to return to sport after lower-extremity injury. The VHP and MAT tests may also be useful on-site screening tools to help identify athletes who may be at increased risk for lower-extremity injury. Future studies should evaluate the validity, sensitivity, and specificity of the MAP and VHP test for identifying lower-extremity asymmetries in patients recovering from lower-extremity injury and in healthy populations. If the VHP and MAT tests are found to be valid, sensitive, and specific measures for identifying lower-extremity asymmetries, these tests may be useful tools to determine the readiness of an athlete to safely return to sport following injury, to predict risk for lower-extremity injury, and to guide prevention programs.

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Acknowledgments

The authors would like to acknowledge funding support from NFL Charities (14). The authors also would like to acknowledge funding support from National Institutes of Health/NIAMS Grants R01-AR049735, R01-AR05563, and R01-AR056259. The authors would like to thank St. Xavier High School, especially John Brehm and Michael Gordon, and Boone County School District, Kentucky, especially School Superintendent Dr. Brian Blavatt, for use of the school facilities in this study.

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References

1. Adirim, TA and Cheng, TL. Overview of injuries in the young athlete. Sports Med 33: 75-81, 2003.
2. Arendt, E and Dick, R. Knee injury patterns among men and women in collegiate basketball and soccer. NCAA data and review of literature. Am J Sports Med 23: 694-701, 1995.
3. Baumhauer, J, Alosa, D, Renstrom, A, Trevino, S, and Beynnon, B. A prospective study of ankle injury risk factors. Am J Sport Med 23: 564-570, 1995.
4. Boden, BP, Dean, GS, Feagin, JA, and Garrett, WE. Mechanisms of anterior cruciate ligament injury. Orthopedics 23: 573-578, 2000.
5. Brosky, JA Jr, Nitz, AJ, Malone, TR, Caborn, DN, and Rayens, MK. Intrarater reliability of selected clinical outcome measures following anterior cruciate ligament reconstruction. J Orthop Sports Phys Ther 29: 39-48, 1999.
6. Cascio, BM, Culp, L, and Cosgarea, AJ. Return to play after anterior cruciate ligament reconstruction. Clin Sports Med 23: 395-408, ix, 2004.
7. Ernst, G, Moore, J, VanLunen, B, and Ball, D. Pondering plyometrics. J Orthop Sports Phys Ther 25: 350-352, 1997.
8. Ferretti, A, Papandrea, P, Conteduca, F, and Mariani, PP. Knee ligament injuries in volleyball players. Am J Sports Med 20: 203-207, 1992.
9. Ford, KR, Myer, GD, Smith, RL, Vianello, RM, Seiwert, SL, and Hewett, TE. A comparison of dynamic coronal plane excursion between matched male and female athletes when performing single leg landings. Clin Biomech 21: 33-40, 2006.
10. Giza, E, Fuller, C, Junge, A, and Dvorak, J. Mechanisms of foot and ankle injuries in soccer. Am J Sports Med 31: 550-554, 2003.
11. Hawkins, RD and Fuller, CW. A prospective epidemiological study of injuries in four English professional football clubs. Br J Sports Med 33: 196-203, 1999.
12. Heidt, RS Jr, Sweeterman, LM, Carlonas, RL, Traub, JA, and Tekulve, FX. Avoidance of soccer injuries with preseason conditioning. Am J Sports Med 28: 659-662, 2000.
13. Hewett, TE, Lindenfeld, TN, Riccobene, JV, and Noyes, FR. The effect of neuromuscular training on the incidence of knee injury in female athletes. A prospective study. Am J Sports Med 27: 699-706, 1999.
14. Hewett, TE, Myer, GD, Ford, KR, Heidt, RS Jr, Colosimo, AJ, and Divine, JG. Pre-season Football combine testing to isolate neuromuscular deficits predictive of ACL injury and reinjury risk. Cincinnati Children's Hospital Medical Center, NFL Charities, 2007.
15. Hewett, TE, Myer, GD, Ford, KR, Heidt, RS Jr, Colosimo, AJ, McLean, SG, van den Bogert, AJ, Paterno, MV, and Succop, P. Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes: A prospective study. Am J Sports Med 33: 492-501, 2005.
16. Hewett, TE, Paterno, MV, and Myer, GD. Strategies for enhancing proprioception and neuromuscular control of the knee. Clin Orthop 402: 76-94, 2002.
17. Hootman, JM, Dick, R, and Agel, J. Epidemiology of collegiate injuries for 15 sports: Summary and recommendations for injury prevention initiatives. J Athl Train 42: 311-319, 2007.
18. Jamshidi, AA, Olyaei, GR, Heydarian, K, and Talebian, S. Isokinetic and functional parameters in patients following reconstruction of the anterior cruciate ligament. Isokinet Exerc Sci 13: 267-272, 2005.
19. Keays, SL, Bullock-Saxton, JE, Newcombe, P, and Keays, AC. The relationship between knee strength and functional stability before and after anterior cruciate ligament reconstruction. J Orthop Res 21: 231-237, 2003.
20. Klein, KK. Asymmetries in the pelvis and legs and their implications in knee injury. Am Correct Ther J 24: 93-95, 1970.
21. Knapik, JJ, Bauman, CL, Jones, BH, Harris, JM, and Vaughan, L. Preseason strength and flexibility imbalances associated with athletic injuries in female collegiate athletes. Am J Sports Med 19: 76-81, 1991.
22. Kobayashi, A, Higuchi, H, Terauchi, M, Kobayashi, F, Kimura, M, and Takagishi, K. Muscle performance after anterior cruciate ligament reconstruction. Int Orthop 28: 48-51, 2004.
23. Kvist, J, Ek, A, Sporrstedt, K, and Good, L. Fear of re-injury: A hindrance for returning to sports after anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc 13: 393-397, 2005.
24. Mandelbaum, BR, Silvers, HJ, Watanabe, D, Knarr, J, Thomas, S, Griffin, L, Kirkendall, DT, and Garrett, WJ. Effectiveness of a neuromuscular and proprioceptive training program in preventing the incidence of ACL injuries in female athletes: Two-year follow up. Am J Sport Med 33: 1003-1010, 2005.
25. Mattacola, CG, Perrin, DH, Gansneder, BM, Gieck, JH, Saliba, EN, and McCue, FC. 3rd Strength, functional outcome, and postural stability after anterior cruciate ligament reconstruction. J Athl Train 37: 262-268, 2002.
26. McKay, GD, Goldie, PA, Payne, WR, and Oakes, BW. Ankle injuries in basketball: Injury rate and risk factors. Br J Sports Med 35: 103-108, 2001.
27. McKay, GD, Goldie, PA, Payne, WR, Oakes, BW, and Watson, LF. A prospective study of injuries in basketball: A total profile and comparison by gender and standard of competition. J Sci Med Sport 4: 196-211, 2001.
28. Mikkelsen, C, Werner, S, and Eriksson, E. Closed kinetic chain alone compared to combined open and closed kinetic chain exercises for quadriceps strengthening after anterior cruciate ligament reconstruction with respect to return to sports: A prospective matched follow-up study. Knee Surg Sports Traumatol Arthrosc 8: 337-342, 2000.
29. Myer, GD, Paterno, MV, Ford, KR, Quatman, CE, and Hewett, TE. Rehabilitation after Anterior cruciate ligament reconstruction: Criteria based progression through the return to sport phase. J Orthop Sports Phys Ther 36: 385-402, 2006.
30. Myklebust, G, Engebretsen, L, Braekken, IH, Skjolberg, A, Olsen, OE, and Bahr, R. Prevention of anterior cruciate ligament injuries in female team handball players: A prospective intervention study over three seasons. Clin J Sport Med 13: 71-78, 2003.
31. NFHS. High School Participation Survey. Indianapolis: National Federation of State High School Associations, 2007.
32. Noyes, FR, Barber, SD, and Mangine, RE. Abnormal lower limb symmetry determined by function hop tests after anterior cruciate ligament rupture. Am J Sports Med 19: 513-518, 1991.
33. Olsen, OE, Myklebust, G, Engebretsen, L, and Bahr, R. Injury mechanisms for anterior cruciate ligament injuries in team handball: A systematic video analysis. Am J Sports Med 32: 1002-1012, 2004.
34. Orchard, J, Seward, H, McGivern, J, and Hood, S. Intrinsic and extrinsic risk factors for anterior cruciate ligament injury in Australian footballers. Am J Sports Med 29: 196-200, 2001.
35. Paterno, MV, Ford, KR, Myer, GD, Heyl, R, and Hewett, TE. Biomechanical limb asymmetries in female athletes 2 years following ACL reconstruction. Clin J Sport Med 17: 258-262, 2007.
36. Paterno, MV, Ford, KR, Myer, GD, Heyl, R, and Hewett, TE. Limb asymmetries in landing and jumping 2 years following anterior cruciate ligament reconstruction. Clin J Sport Med 17: 258-62, 2007.
37. Pauole, K, Madole, K, Garhammer, J, Lacourse, M, and Rozene, R. Reliability and validity of the T-test as a measure of agility, leg power, and leg speed in college-aged men and women. Journal of Strength and Conditioning Research 14: 443-450, 2000.
38. Portney, LG and Watkins, MP. Foundations of Clinical Research. Norwalk, CT: Appleton & Lange, 2000.
39. Salmon, L, Russell, V, Musgrove, T, Pinczewski, L, and Refshauge, K. Incidence and risk factors for graft rupture and contralateral rupture after anterior cruciate ligament reconstruction. Arthroscopy 21: 948-957, 2005.
40. Wright, RW, Dunn, WR, Amendola, A, Andrish, JT, Bergfeld, J, Kaeding, CC, Marx, RG, McCarty, EC, Parker, RD, Wolcott, M, Wolf, BR, and Spindler, KP. Risk of tearing the intact anterior cruciate ligament in the contralateral knee and rupturing the anterior cruciate ligament graft during the first 2 years after anterior cruciate ligament reconstruction: A prospective MOON cohort study. Am J Sports Med 35: 1131-1134, 2007.
Keywords:

functional test; vertical hop test; modified agility T-test; injury prevention

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