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Neuromuscular Training Improves Knee Kinematics, in Particular in Valgus Aligned Adolescent Team Handball Players of Both Sexes

Barendrecht, Maarten1,2; Lezeman, Harry C A1,3; Duysens, Jacques4,5; Smits-Engelsman, Bouwien C M1,6

Journal of Strength and Conditioning Research: March 2011 - Volume 25 - Issue 3 - p 575-584
doi: 10.1519/JSC.0b013e3182023bc7
Original Research
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Barendrecht, M, Lezeman, HCA, Duysens, J, and Smits-Engelsman, BCM. Neuromuscular training improves knee kinematics, in particular in valgus aligned adolescent team handball players of both sexes. J Strength Cond Res 25(X): 000-000, 2011-The purpose of this study was to investigate the effects of added neuromuscular training (NMT), as compared to just regular training (RT), on lower extremity kinematics and single leg stability in adolescent team handball players of both sexes and to investigate whether these effects are more evident in valgus aligned athletes. Eighty adolescent team handball players (NMT: n = 49, RT: n = 31) were tested on knee kinematics in a drop jump and single leg stability in a 1-leg hop test. Based on the initial results in the drop jump test, both groups were subdivided into an above-average valgus aligned (AAVA; NMT: n = 27, RT: n = 22) and a below average valgus aligned (NMT: n = 22, RT: n = 9) group. All groups received 10 weeks of handball training either without (RT) or with in-season NMT. A significant interaction of training and valgus group was found for all absolute and for 2 out of 4 normalized knee distances in the drop jump test (p < 0.024) and for contact time after the first landing (p = 0.029). The AAVA-NMT group showed the largest relative progression (18-37%) for all these parameters. In the 1-leg hop test, a significant effect of NMT compared to RT was found for both legs (p < 0.042). Compared to RT alone, added in-season NMT has the greatest benefits on knee kinematics and single leg stability, in particular in AAVA adolescent team handball players of both sexes. The results of this study suggest that adolescent team handball players of both sexes should be given NMT, 20 minutes twice a week for 10 weeks to improve landing kinematics and single leg stability. “At risk” players with higher initial valgus angles will benefit most from this NMT.

1Avans+, University for Professionals, Breda, The Netherlands; 2Private Practice for Sports Physical Therapy, The Hague, The Netherlands; 3Dutch Central Military Hospital, Department of Physical Therapy, Utrecht, The Netherlands; 4Sint Maartenskliniek Research, Development & Education, Nijmegen, The Netherlands; 5Department of Biomedical Kinesiology, Faculty Of Kinesiology and Rehabilitation Sciences, Katholieke Universiteit Leuven, Belgium; and 6Research Center for Movement Control and Neuroplasticity, Department of Biomedical Kinesiology, Faculty of Kinesiology and Rehabilitation Sciences, Katholieke Universiteit Leuven, Belgium

Address correspondence to M. Barendrecht, maartenbarendrecht@hotmail.com.

Funding: This study was sponsored by the RGF Zuid-Holland, Regional Department of the Dutch Physical Therapy Association.

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Introduction

Preventive training programs can reduce the incidence of sports injuries of the lower extremity in general (12,35,37,41) and of knee- or anterior cruciate ligament (ACL) injuries (4,14,23,29) and ankle injuries (2,5,40) in particular. Although it is not clear to what extent the different components of these programs are responsible for the reductions in injury risk, neuromuscular training (NMT) aimed at reduction of knee valgus angles and improvement of single-leg stability and balance is thought to play an important role in injury prevention (11,15,39). Neuromuscular training programs have been shown to make significant reductions in peak landing forces (17,20), knee valgus and varus torques (17,28) and to make improvements on knee valgus angle (32), single limb stability (36), balance (18), or landing error score (6).

It has been established that increased knee valgus angles are related to increased ACL injury risk (16,33) Because several studies have found increased valgus angles of the knee in female athletes compared to male athletes (8,9,21), changes in lower extremity biomechanics after NMT have predominantly been studied in female athletes (10,17,20,25,28,32,36). However, several neuromuscular and proprioceptive training programs have been successful in reducing injury risk in male athletes as well (2,4,7,34,40). The question remains whether after added NMT (as compared to regular training [RT] alone), improvements in knee valgus angle and single leg stability will not only occur in female, but also in male athletes and especially in those athletes with poor knee alignment (36). Specifically targeting both male and female “high risk athletes” could improve the effectiveness of NMT and further reduce injury rates. Recently, DiStefano et al. (6) studied the improvement in LESS scores (Landing Error Scoring System, a composed measurement tool of landing technique errors in the drop jump) after a 10- to 15-minute warm-up program for all youth soccer training sessions during 1 season. They found similar improvements in male and female players, but a significantly larger improvement (p < 0.05) was found for athletes with poor initial LESS scores (as compared to athletes with moderate to excellent LESS sores). Similarly, Meyer et al. (25) found a significant decrease in mean peak knee abduction torque for the left and right legs during the drop vertical jump by 13% (p = 0.033) in “high risk” female athletes after a 7 week (3 × per week) NMT program, whereas “low risk” athletes showed no significant changes. However, neither of these studies compared the effect of their program with the effect of regular sports training. Furthermore, because NMT programs include sport-specific exercises (26) and knee valgus angles differ between athletes in different sports (13), it is necessary to investigate the effects of these programs on kinematics of “high” vs. “low risk” athletes for each sport separately. In this study, an in-season NMT program implemented in regular team handball training was tested and the question was asked whether such training proved to be more effective in a “high” vs. a “low risk” group, irrespective of sex. The hypothesis was that, compared to RT alone, NMT added to RT would improve knee valgus angles and single leg hop performance, as measures of safe performance, especially in valgus aligned team handball players, irrespective of sex.

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Methods

Experimental Approach to the Problem

To compare the effects of NMT as added to RT, with RT alone and to investigate whether these effects would be greater in athletes showing “high risk” initial knee valgus angles (irrespective of sex), a controlled cohort repeated-measures design was used. An NMT program was implemented in regular handball training at a Dutch handball club with participation of four teams and their trainers. Athletes from 4 teams from 2 other Dutch handball clubs along with their trainers were asked to participate in the study as RT group. They received their usual handball training. Both NMT and RT groups consisted of 2 male and two female teams that trained separately. All groups trained for a period of 10 weeks at the beginning of the indoor season. The indoor season starts in October. Before that all youth teams participate in an outdoor season starting in August. Pre and posttesting for drop jump landing kinematics and single-leg hop performance for both NMT and RT groups was conducted by the first and second authors on the first 2 days in the weeks directly before and after the intervention period. Athletes trained in their usual groups, and both athletes and their trainers were blinded to the initial results on knee valgus angles.

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Subjects

Athletes were included when they played handball in either 1 of 2 age groups (16-19 or 13-16 years of age). These age groups are at high risk for ACL injury (11) and in team handball show an overall injury incidence level similar to senior team handball players (34). Athletes who were injured and not fully recovered before the first test were excluded from the study. No previously ACL injured athletes participated in the study. Before participation, all athletes and their parents were informed about the purpose of the study and possible risks and gave their written informed consent. The study complied with the requirements of the declaration of Helsinki. Ninety-three athletes (NMT: n = 55, RT: n = 38) agreed to participate in the study (Figure 1 for study design). Thirteen athletes (6NMT, 7RT) did not fully participate in the second test and were excluded from the study, leaving 80 athletes for complete analysis (NMT: n = 49, RT: n = 31). Based on minimum knee distance values measured upon landing or upon take-off from the drop jump in the pretest subjects were assigned to an above-average valgus aligned (AAVA) and a below average valgus aligned (BAVA) group (for further details of the kinematic variables see Appendix 1). This resulted in 4 groups for comparison (NMT AAVA, n = 27; NMT BAVA, n = 22; RT AAVA, n = 22; and RT BAVA, n = 9). Table 1 shows baseline values for age, height, weight and minimum normalized knee distances.

Figure 1

Figure 1

Table 1

Table 1

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Procedures

Training Protocol

For this study, a training program was composed based on adaptations of earlier NMT studies (14,29,35). The present NMT program (see Appendix 2) consisted of a standard warm-up including agility exercises (6 minutes), balance, and coordination exercises on both a wobble board and a mat (both 4 minutes) and strength- and plyometric exercises at the end of the training (6 minutes). Training was given by the usual handball trainers. Before the start of the training program, these trainers were instructed on correct application of the techniques and received an instruction book and DVD on which the total program was demonstrated. The NMT was given twice a week during the whole period between the 2 test sessions. In the same period, subjects from the RT group received their usual handball training. Trainers of the RT group were not familiar with the principles of NMT.

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Testing Procedures

Before and after the intervention period, both groups were tested for knee valgus angle, knee flexion angle, and contact time in a drop jump test. Furthermore, they were examined for single leg stability in the 1-leg hop test. These variables where chosen because NMT is aimed at softer landing techniques, decreasing knee valgus angles, and improved single leg stability. Detailed information of all testing procedures is given in Appendix 1.

The procedure of the drop-jump test has been described by Noyes et al. (32). However in our test protocol, athletes landed on a contact mat and the highest jump (of 2 trials), measured by means of this contact mat, was used as reference for all analyses. This procedure had significant (p < 0.01) high test-retest reliability for absolute (cm) and normalized (% of hip distance) knee-separation distances (intraclass correlation coefficient [ICC]: prelanding, 0.74 [SEM: 0.6 cm] and 0.68 [SEM: 2.4%]; landing, 0.93 [SEM: 0.5 cm] and 0.91 [SEM: 1.9%]; take-off, 0.95 [SEM: 0.5 cm] and 0.94 [SEM: 1.6%], respectively) and minimum knee distance (ICC: absolute 0.96 [SEM: 0.4 cm], normalized 0.95 [SEM: 1.5%]) (see Appendix 1).

The 1-leg hop test was performed as described by Noyes et al. (31) and has been shown to have high test-retest reliability (ICC: 0.92-0.96; SEM 4.56-4.62 cm) in healthy subjects by several authors (3,38).

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Statistical Analyses

Statistical analyses were conducted using SPSS 13.0 (SPSS, Inc., Chicago, IL, USA). One-way analysis of variance (ANOVA) was used to test differences in mean age, height, weight, and exposure time for NMT and RT groups and for AAVA and BAVA groups.

An ANOVA repeated-measures design was used to analyze the effect for training (pre and postsession) and interactions between either NMT or RT and BAVA or AAVA on the following variables: contact time, knee flexion angle, and knee-separation distances (for the Drop Jump test) and horizontal distance (for the 1-Leg Hop test). Additionally, a linear regression analysis was used to predict variance in pre-posttest change for minimum normalized knee distance, contact time and knee flexion angle in the drop jump.

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Results

Training Participation

Mean overall training participation per week was 2.2 (±0.73) sessions with 2.2 (±0.87) sessions for the NMT AAVA group, 1.9 (±0.63) sessions for the NMT BAVA group, 2.5 (±0.52) sessions for the RT AAVA group and 2.7 (±0.68) sessions for the RT BAVA group. One-way ANOVA showed a significant difference in training participation (F(1.3) = 3,50, p = 0.019). Post hoc analysis using Gabriel's procedure showed a significant difference between the NMT BAVA and RT BAVA groups, Other group comparisons showed no significant differences in training participation. No significant difference in participation of the NMT sessions was found between the NMT AAVA (times per week 1.45 ± 0.44) and the NMT BAVA group (1.65 ± 0.41).

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Drop Jump Test

Knee Distances

Overall training resulted in greater knee distances (Table 2). Between sessions, a significant main effect was found for all absolute knee distances (p < 0.001) and for all normalized knee distances (p < 0.023). Nevertheless, there were clear group differences.

Table 2

Table 2

Table. Ca

Table. Ca

The NMT AAVA group showed the largest increase for most absolute and normalized knee distances (Table 2). Comparison of relative improvements (as percentage of baseline values) showed the highest increases in all absolute and normalized knee distances for the NMT AAVA group (18-37%). This was confirmed by a significant interaction of training and valgus group, found for all absolute knee distances (p < 0.025), and for normalized knee distances for prelanding and landing (p < 0.007). Normalized knee distances for takeoff and minimum knee distance showed the same trend (Table 2). In addition, linear regression analysis showed that in the NMT groups initial minimum normalized knee distance predicted 52% of the variance in pre-posttest change for minimum normalized knee distance (R = 0.518; SEE = 10.33, p < 0.001), whereas in the RT groups, no significant relation was found (R = 0.044; SEE = 9.56, p = 0.812).

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Contact Time and Knee Flexion Angle

The success of the training was also evaluated in terms of contact time and knee flexion angle (which are expected to increase after training) as measures of softer landing technique. Between sessions, there was an overall significant increase (p = 0.001) in contact time after the first landing in the drop jump test (Table 3). In addition, a significant interaction of training group and valgus group was found (p = 0 0.029) for contact time and a trend toward effect of NMT (p = 0.069). The AAVA NMT group showed by far the greatest absolute and relative (see also Figure 2) increase in contact time. Linear regression analysis showed that in the NMT groups, initial minimum normalized knee distance predicted 33% of the variance in pre-posttest change for knee flexion angle (R = 0.333; SEE = 111.69, p = 0.020) In the RT groups, no significant relation was found (R = 0.235; SEE = 73.47, p = 0.204).

Table 3

Table 3

Figure 2

Figure 2

No significant interaction was found for maximum knee flexion angle after the first landing in the drop jump test. However, linear regression analysis showed that in the NMT groups, initial minimum normalized knee distance predicted 59% of the variance in pre-posttest change for knee flexion angle (R = 0.589; SEE = 7.68, p < 0.001), whereas in the RT groups, no significant relation was found (R = 0.189; SEE = 8.13, p = 0.308).

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One-Leg Hop Test

Statistical analysis revealed that for the 1-leg hop test a significant main effect in 1-leg hop distance between sessions was found for both dominant (p = 0.005) and nondominant leg (p < 0.001). The combined NMT groups showed a significantly (p < 0.043) higher effect on 1-leg hop distance for both legs compared to the combined RT groups.

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Discussion

This study investigated the effect of 20 minutes of NMT as added to RT twice a week for 10 weeks on lower extremity kinematics and single leg stability of adolescent team handball players The first result of this study was that a program based on Olsen et al. (35) resulted in improvements in knee valgus angle, contact time, and knee flexion angles (see Tables 2 and 3), thereby confirming the results of earlier studies (28,32,36). These changes are known to be related to a decrease in risk of injury (16,33).

In addition, a novel finding is that the improvement was not sex-specific but occurred in both male and female adolescent team handball players with initial above-average valgus angles (see Tables 1-3). Recently, DiStefano et al. (6) found similar improvements in male and female youth soccer players. However, they used a more general measurement tool (LESS score) and did not compare their intervention to RT.

Importantly, we were able to show that in-season NMT added to regular handball training had a beneficial effect in particular on AAVA athletes (see Figure 2). These improvements are in line with results of DiStefano et al. (6) who found a significantly larger improvement (p < 0.05) in LESS scores for adolescent soccer players of both sexes with poor initial LESS scores as compared to those with moderate to excellent LESS sores. Accordingly, Myer et al. (25) found significant improvements on peak knee abduction torque in “high risk” athletes compared to in “low risk” athletes after an NMT program. In our study, initial minimum normalized knee distance in the NMT groups predicted 52% of the variance in pre-posttest change for minimum normalized knee distance (R = 0.518; SEE = 10.33, p < 0.001), which was even higher than the 40% variance predicted by initial knee abduction moment Myer et al. found in their study. Moreover, Myer et al. only looked at female athletes in a preseason program, whereas DiStefano et al looked at athletes of both sexes in an in-season program as we did in our study. This study is the only one which can attribute the additional effects to NMT, because NMT was compared to RT.

The drop jump test seemed to disclose the largest changes, but the 1-leg hop test was also sensitive to change caused by the intervention (see Table 4).

Table 4

Table 4

A significant beneficial effect of NMT over RT on single leg hop distance was found for both legs (see Table 4). Although this effect was predominantly caused by a lack of improvement in the RT AAVA group, whereas the NMT AAVA group showed improvements similar to the BAVA groups (see Table 4), no significant interaction of training and valgus group was found.

The overall results for hop distance of the NMT groups (see Table 4) are similar to the results found by Holm et al. (18) in a study on NMT for adult female team handball players. Myer et al. (28) found improved hop distances in adolescent female athletes after an intensive preseason training program. Again these studies only looked at female athletes, whereas we studied athletes of both sexes. The observed significant mean improvements for both legs for athletes in the NMT groups, compared to athletes in the RT groups, supports the hypothesis that in-season NMT added to RT has beneficial effects on single leg hop performance specifically in AAVA adolescent team handball players as compared to RT alone. The NMT program used in our study was based on an earlier study of Olsen et al. (35) on adolescent team handball players. It would be interesting to know whether the reduction in injury risk found in their study can be attributed to the improvements in knee kinematics and single leg stability as found in our study. Further research is needed to investigate this assumption.

Female athletes show up to 5 times higher ACL-injury rates compared to male athletes (1,30). Because of these higher rates, most studies on changes in biomechanics after an NMT program have only looked at female athletes (17,27,28,32). However, despite a lower risk, male athletes still account for two-thirds of ACL injuries in sports (19,22) The question arises whether predisposing factors, such as knee valgus alignment, which are more evident in female athletes in general, might also be found in male athletes that are prone to ACL injury. Eleven out of 34 boys (32.4%) in our study showed above-average knee valgus angles. Our cut-off point was based upon the mean value for minimum normalized knee distance of all athletes in this study. Noyes et al. (32) found 75% of boys in their study on the drop jump test to have “distinctly abnormal lower limb valgus alignment” with a cut-off point of 60% for normalized knee distance upon landing. Neither of these cut-off points has been validated for ACL-injury risk. Hewett et al. (16) found a 7.6° (p < 0.01) greater maximum knee abduction angle (measured in a 3d laboratory test) upon landing for female ACL injured athletes compared to noninjured athletes and validated a cut-off point for high risk and low risk female athletes, but this test is not easily applicable in field situations. Although the relation found by Hewett et al. has not been established in male athletes, the combined findings of the present and earlier studies (6,32) indicate that screening for knee valgus angle deficits using simple kinematic analysis should be performed on boys and on girls. Identified AAVA athletes should then be the primary target group for NMT.

Our study has several shortcomings: (a) The group assignment in our study was based on a statistical method using the mean value and SD for normalized knee distances of all athletes after the first test. Like the classifications of Noyes et al. (32) or DiStefano et al. (6), the way athletes were classified cannot be generalized to other athletes nor has our method been validated by comparison with other measures or prospective studies. Future research is needed to validate a cut-off point for knee injury risk in some simple field test determining whether or not an athlete should be subjected to NMT. (b) A considerable difference in training intensity for the BAVA athletes in the NMT group compared to the RT group could have influenced the results of our study. Our results however have shown the largest differences in improvements in AAVA athletes in the NMT group compared to the RT group and for these groups no significant difference in mean training exposure was found. (c) Groups in our study were not randomly assigned. Possible bias could have been that differences in training methods in different clubs or teams could have accounted for differences in outcome. However, both groups trained for the same sport and did not change training methods compared to the previous season. In addition,

AAVA and BAVA athletes in either NMT or RT groups did participate in training sessions together. Still, further research in randomized controlled studies is needed to confirm the results of our study.

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Practical Applications

Based on the results of this study, it should be considered to add in-season NMT is to RT of adolescent team handball players of both sexes. Twenty minutes of NMT twice a week during a period of 10 weeks at the start of the season may significantly reduce knee valgus angles, and improve single leg stability, specifically in athletes with initial above-average knee valgus angles This NMT should consist of a warm-up including agility exercises, balance, and coordination exercises both on a wobble board and a mat and strength- and plyometric exercises at the end of the training.

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Acknowledgments

This study was sponsored by the RGF Zuid-Holland, regional department of the Dutch Physical Therapy Association. De Haagse Hogeschool, Dep. Bewegingstechnologie, The Hague, The Netherlands provided software for contact time measurement. There was no conflict of interest. Specials thanks to Eugene Rameckers, for assistance in manuscript preparation and Koos Herrewijnen for making software adjustments.

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References

1. Agel, J, Arendt, EA, and Bershadsky, B. Anterior cruciate ligament injury in national collegiate athletic association basketball and soccer: A 13-year review. Am J Sports Med 33: 524-530, 2005.
2. Bahr, R, Lian, O, and Bahr, IA. A twofold reduction in the incidence of acute ankle sprains in volleyball after the introduction of an injury prevention program: A prospective cohort study. Scand J Med Sci Sports 7: 172-177, 1997.
3. Bolgla, LA and Keskula, DR. Reliability of lower extremity functional performance tests. J Orthop Sports Phys Ther 26: 138-142, 1997.
4. Caraffa, A, Cerulli, G, Projetti, M, Aisa, G, and Rizzo, A. Prevention of anterior cruciate ligament injuries in soccer. A prospective controlled study of proprioceptive training. Knee Surg Sports Traumatol Arthrosc 4: 19-21, 1996.
5. Cumps, E, Verhagen, E, and Meeusen, R. Efficacy of a sports specific balance training programme on the incidence of ankle sprains in basketball. J Sports SciMed 6: 212-219, 2007.
6. DiStefano, LJ, Padua, DA, DiStefano, MJ, and Marshall, SW. Influence of age, sex, technique, and exercise program on movement patterns after an anterior cruciate ligament injury prevention program in youth soccer players. Am J Sports Med 37: 495-505, 2009.
7. Emery, CA, Cassidy, JD, Klassen, TP, Rosychuk, RJ, and Rowe, BH. Effectiveness of a home-based balance-training program in reducing sports-related injuries among healthy adolescents: A cluster randomized controlled trial. CMAJ 172: 749-754, 2005.
8. Ford, KR, Myer, GD, and Hewett, TE. Valgus knee motion during landing in high school female and male basketball players. Med Sci Sports Exerc 35: 1745-1750, 2003.
9. Ford, KR, Myer, GD, Toms, HE, and Hewett, TE. Gender differences in the kinematics of unanticipated cutting in young athletes. Med Sci Sports Exerc 37: 124-129, 2005.
10. Grandstrand, SL, Pfeifer, RP, Sabick, MB, DeBelisio, M, and Shea, KG. The effects of a commercially available warm-up program on landing mechanics in female youth soccer players. J Strength Cond Res 20: 331-335, 2006.
11. Griffin LY, Albohm MJ, Arendt EA, Bahr R, Beynnon BD, Demaio M, Dick RW, Engebretsen L, Garrett WE Jr, Hannafin JA, Hewett TE, Huston LJ, Ireland ML, Johnson RJ, Lephart S, Mandelbaum BR, Mann BJ, Marks PH, Marshall SW, Myklebust G, Noyes FR, Powers C, Shields C Jr, Shultz SJ, Silvers H, Slauterbeck J, Taylor DC, Teitz CC, Wojtys EM, and Yu B. Understanding and preventing noncontact anterior cruciate ligament injuries: A review of the Hunt Valley II meeting, January 2005. Am J Sports Med 34: 1512-1532, 2006.
12. Heidt Jr RS, 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. Herrington, L. Knee valgus angle during landing tasks in female volleyball and basketball players. J Strength Cond Res 2009 December 4. [Epub ahead of print]
14. Hewett, TE, Lindenfeld, TN, Riccobene, JV, and Noyes, FR. The effect of neuromuscular training on the incidence of knee injury in female athletes. Am J Sports Med 27: 699-706, 1999.
15. Hewett, TE, Myer, GD, and Ford, KR. Reducing knee and anterior cruciate ligament injuries among female athletes: A systematic review of neuromuscular training interventions. J Knee Surg 18: 82-88, 2005.
16. 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.
17. Hewett, TE, Stroupe, AL, Nance, TA, and Noyes, FR. Plyometric training in female athletes. Decreased impact forces and increased hamstring torques. Am J Sports Med 24: 765-773, 1996.
18. Holm, I, Fosdahl, MA, Friis, A, Risberg, MA, Myklebust, G, and Steen, H. Effect of neuromuscular training on proprioception, balance, muscle strength, and lower limb function in female team handball players. Clin J Sport Med 14: 88-94, 2004.
19. 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.
20. Irmischer, BS, Harris, C, Pfeiffer, RP, DeBeliso, MA, Adams, KJ, and Shea, KG. Effects of a knee ligament injury prevention exercise program on impact forces in women. J Strength Cond Res 18: 703-707, 2004.
21. Kernozek, TW, Torry, MR, van Hoof, H, Cowley, H, and Tanner, S. Gender differences in frontal and sagittal plane biomechanics during drop landings. Med Sci Sports Exerc 37: 1003-1012, 2005.
22. Majewski, M, Susanne, H, and Klaus, S. Epidemiology of athletic knee injuries: A 10-year study. Knee 13: 184-188, 2006.
23. Mandelbaum BR, Silvers HJ, Watanabe DS, Knarr JF, Thomas SD, Griffin LY, Kirkendall DT, and Garrett W Jr. Effectiveness of a neuromuscular and proprioceptive training program in preventing anterior cruciate ligament injuries in female athletes. 2-year follow-up. Am J Sports Med 33: 1003-1010, 2005.
24. Markovic, G, Dizdar, D, Jukic I, and Cardinale M. Reliability and factorial validity of squat and countermovement jump tests. J Strength Cond Res 18: 551-555, 2004.
25. Myer, GD, Ford, KR, Brent, JL, and Hewett, TE. Differential neuromuscular training effects on ACL injury risk factors in“high-risk” versus “low-risk” athletes. BMC Musculoskelet Disord 8: 39, 2007.
26. Myer, GD, Ford, KR, and Hewett, TE. Rationale and clinical techniques for anterior cruciate ligament injury prevention among female athletes. J Athl Train 39: 352-364, 2004.
27. Myer, GD, Ford, KR, McLean, SG, and Hewett, TE. The effects of plyometric versus dynamic stabilization and balance training on lower extremity biomechanics. Am J Sports Med 34: 445-455, 2006.
28. Myer, GD, Ford, KR, and Palumbo, JP. Neuromuscular training improves performance and lower-extremity biomechanics in female athletes. J Strength Cond Res 19: 51-60, 2005.
29. 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.
30. Myklebust, G, Maehlum, S, Holm, I, and Bahr, R. A prospective cohort study of anterior cruciate ligament injuries in elite Norwegian team handball. Scand J Med Sci Sports 8: 149-153, 1998.
31. 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.
32. Noyes, FR, Barber-Westin, SD, Fleckenstein, C, Walsh, C, and West, J. The drop jump screening test, difference in lower limb control by gender and effect of neuromuscular training in female athletes. Am J Sports Med 33: 378-387, 2005.
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. Olsen, OE, Myklebust, G, Engebretsen, L, and Bahr, R. Injury pattern in youth team handball: A comparison of two prospective registration methods. Scand J Med Sci Sports 16: 426-432, 2006.
35. Olsen, OE, Myklebust, G, Engebretsen, L, Holme, I, and Bahr, R. Exercises to prevent lower limb injuries in youth sports: cluster randomised controlled trial. BMJ 330: 449, 2005.
36. Paterno, MV, Myer, GD, Ford, KR, and Hewett, TE. Neuromuscular training improves single-limb stability in young female athletes. J Orthop Sports Phys Ther 34: 305-316, 2004.
37. Petersen W, Braun C, Bock W, Schmidt K, Weimann A, Drescher W, Eiling E, Stange R, Fuchs T, Hedderich J, and Zantop T. A controlled prospective case control study of a prevention training program in female team handball players: The German experience. Arch Orthop Trauma Surg 125: 614-621, 2005.
38. Ross, MD, Langford, B, and Whelan, PJ. Test-retest reliability of 4 single-leg horizontal hop tests. J Strength Cond Res 16: 617-622, 2002.
39. Taube, W, Gruber, M, and Gollhofer, A. Spinal and supraspinal adaptations associated with balance training and their functional relevance. Acta Physiol (Oxf). 193: 101-116, 2008.
40. Verhagen, E, van der Beek, A, Twisk, J, Bouter, L, Bahr, R, and van Mechelen, W. The effect of a proprioceptive balance board training program for the prevention of ankle sprains: A prospective controlled trial. Am J Sports Med 32: 1385-1393, 2004.
41. Wedderkopp, N, Kaltoft, M, Lundgaard, B, Rosendahl, M, and Froberg, K. Prevention of injuries in young female players in European team handball. A prospective intervention study. Scand J Med Sci Sports 9:41-47, 1999.
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Appendix 1: Testing Procedures

Subjects first received a standardized specific warm-up including jogging, squat exercises, jump-strides, and jumping up and down a bench. After that, subjects started the testing procedure. For each individual test, the jumping procedure was explained and demonstrated. After the instruction, each subject was allowed 2 warm-up jumps before the actual tests were done. No instructions were given with respect to the actual technique of the jumps. However, for the Drop Jump Test, subjects were instructed not to pull up their legs during the jump.

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Drop Jump Test

The procedure of this test has been described by Noyes et al. (32). Subjects were asked to jump from a box (30 cm high), land on both feet, and immediately jump vertically as high as possible and land on the same spot again. Markers (for measurement of knee kinematics in the frontal plane with a video camera) were placed at the greater trochanter, on the center of the patella and at the lateral malleolus of both legs. Some adjustments were made compared to the procedure as described by Noyes et al. (32). First, subjects were asked to wear stretch shorts and low cut shoes and socks that left the ankle free to minimize marker movement. Second, an additional marker was placed on the lateral epicondyl of the left knee to measure the amount of flexion with a laterally placed camera (operating at 30 frames per second, placed on a stand 102 cm in height, positioned 366 cm on the left side of the box). Third, instead of landing on the ground, subjects were asked to land on a contact mat (Conrad, Netherlands, type 750188; 71 × 40 cm), placed at a 20-cm distance from the box. They then had to jump immediately as high as possible and land on the same mat again. The contact mat was connected to a laptop computer. A computer program (Jumptest2-XP, Netherlands) which registers contact time and flight time in milliseconds and computes jump height (JH) in millimeters (JH = ½gtflight)2), was used to measure the contact time after jumping from the box, This measurement was used to estimate the jump height of the maximal vertical jump. The use of a contact mat has been shown to be a reliable way to measure jump height (24). The highest jump (of 2 trials), measured by means of the contact mat, was used as reference for all analyses. This procedure had significant (p < 0.01) high test-retest reliability for absolute (cm) and normalized (% of hip distance) knee-separation distances (ICC: prelanding, 0.74 [SEM: 0.6 cm] and 0.68 [SEM: 2.4%]; landing, 0.93 [SEM: 0.5 cm] and 0.91 [SEM: 1.9%]; take-off, 0.95 [SEM: 0.5 cm] and 0.94 [SEM: 1.6%], respectively) and minimum knee distance (ICC: absolute 0.96 [SEM: 0.4 cm], normalized 0.95 [SEM: 1.5%]).

Digital video clips of 2 cameras (1 positioned in front and 1 lateral) were captured and saved to the hard drive of a computer for storage and analysis. Images from the frontal camera were analyzed using Software for Analysis of Jumping Mechanics (Sportsmetrics, Cincinnati, OH, USA) for measurements in the coronal plane. As described by Noyes et al. (32), still images of predetermined phases of the drop jump were selected, and in these images, markers were identified in a predetermined sequence. The software calculates the distances between the markers on the hips, knees, and ankles as absolute hip-, knee- and ankle- distances. In addition, the software provides normalized knee and ankle distances (as a percentage of the hip distances in the same jump). These normalized knee and ankle distances are indicative of knee valgus alignment.

The images from the lateral camera were analyzed with a software program developed for goniometric measurements (Fotonaarhoek, The Hague, Netherlands). The frame in which the athlete showed maximum knee flexion was captured for analysis. Knee flexion angle was measured as the angle between the lines from the markers on the left hip and ankle to the marker on the lateral epicondyle of the knee.

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One-Leg Hop Test

The 1-leg hop test was performed as described by Noyes et al. (31) and has been shown to have high test-retest reliability (ICC: 0.92-0.96; SEM 4.56-4.62 cm) in healthy subjects by several authors (3,38). Subjects were asked to stand on 1 leg, jump as far as possible, land on the same leg and keep their balance. Upper extremity movement was not restricted. Subjects alternately hopped twice for each leg starting with their left leg. Hop distance was measured from toe to toe. The mean hop distance of the 2 trials per leg for each test was used for calculation. Furthermore, athletes were asked which leg they would use to kick a ball as far as possible. This leg was labeled as dominant leg. In the total population, 86% (n = 69) were right dominant.

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Appendix 2: Exercise Program

Technique

While landing from a jump, players were instructed to flex their knees and keep them in a straight line with hip and ankle without kneeing-in. The latter instruction was also given for balance exercises on the wobble board. In addition, athletes were instructed to make a soft landing and cutting maneuvers, by flexing their knees during all plyometric and agility exercises. Athletes trained in couples and were instructed to correct each other for incorrect posture or techniques.

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Warm-Up Exercises (6 minutes)

  • Without ball: Jogging, running forward with knee lifts, running forward with heel strikes, running backward with side steps, side shuffle, carioca, running forward with upper body rotations, running with increasing speed, shuttle run.
  • With ball: Running with sidesteps and bouncing, stop jumps with knees bend 90°, small 1-leg jumps with landing on alternative legs, side to side jumps.
  • Alternate exercises: Running with side steps, 1-leg hop twice left, twice right and stop jump, running and cutting, jump shot pass and landing with bend knees, cutting and jump shot.
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Mat Exercises (4 minutes)

  • Couples standing on 1 leg and throwing a ball (both legs).
  • Jump shot from a step box and landing on 2 legs.
  • Step down from a box on 1 leg while catching a ball (both legs).
  • Balance fight on 2 legs and 1 leg.
  • Stop jump on 2 legs while catching a ball and immediately jump 180° (both sides).
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Balance Board Exercises (4 minutes)

  • Standing on 2 legs with knees bent and throwing a ball.
  • Squat exercise (on 2 legs and 1 leg) while throwing a ball.
  • Standing on 1 leg with bent knee while throwing a ball.
  • Standing on 1 leg with bent knee and bouncing (later with eyes shut).
  • Balance fight on 2 legs.
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Plyometric exercises

(Two exercises 15-20 seconds wit 30 seconds rest per session) on a mat

  • Wall jumps.
  • Skate jumps.
  • Forward lunges.
  • Side to side jumps on 2 legs (later on 1 leg).
  • Broad jumps.
  • Bounding.
  • Tuck jumps.
  • Scissor jumps.
  • 180° jumps.
  • One-leg hop and stick (3 seconds, both legs).
  • Squat jumps.
  • Up down and 180° vertical.
  • Two legged jump forward and backward (later on 1 leg).
  • Two legged cross jumps (later on 1 leg).
  • Triple broad jump and vertical.
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Strength Exercises in Couples

  • Squat 2-3 series, 8-10 reps, weight up to max 10% bodyweight.
  • Nordic hamstring 2-3 series 3-10 reps.
Keywords:

biomechanics; sports injury prevention; warm-up; drop jump

© 2011 National Strength and Conditioning Association