Canadian Academy of Sport and Exercise Medicine Position Statement: Neuromuscular Training Programs Can Decrease Anterior Cruciate Ligament Injuries in Youth Soccer Players : Clinical Journal of Sport Medicine

Secondary Logo

Journal Logo

Position Statement

Canadian Academy of Sport and Exercise Medicine Position Statement

Neuromuscular Training Programs Can Decrease Anterior Cruciate Ligament Injuries in Youth Soccer Players

Campbell, Cathy J. BPE, MSc, MD, Dip Sport Med*; Carson, James D. MD, Dip Sport Med*; Diaconescu, Elena D. MD; Celebrini, Rick PT, PhD; Rizzardo, Marc R. Dip Sports Physio, BScPT, MPE, BPE; Godbout, Veronique MD, Dip Sport Med, MA, MedEd, BSc§; Fletcher, Jennifer A. MD, Dip Sport Med; McCormack, Robert MD; Outerbridge, Ross MD, Dip Sport Med**; Taylor, Taryn MSc, MD, Dip Sport Med††; Constantini, Naama MD, DFM, Dip Sport Med‡‡; Cote, Manon MD, Dip Sport Med, BScPT§§

Author Information
Clinical Journal of Sport Medicine 24(3):p 263-267, May 2014. | DOI: 10.1097/JSM.0000000000000068
  • Free
  • Blog Link
  • Podcast


This Canadian Academy of Sport and Exercise Medicine (CASEM) position statement reviews the literature and concludes that youth soccer players and their coaches can decrease the incidence of anterior cruciate ligament (ACL) injuries of the knee through the implementation of neuromuscular training (NMT) programs. Furthermore, we propose a coordinated Canada-wide adoption of such injury prevention programs.


Close to a quarter of a million ACL injuries occur each year in Canada and in the United States.1 Anterior cruciate ligament injuries are common in sports that involve sudden changes of direction, quick decelerations, and awkward landings after a jump.2,3 Anterior cruciate ligament injuries usually result in prolonged postoperative recovery and time away from soccer to complete rehabilitation. There is often significant morbidity associated with ACL injuries as a result of long-term persistent symptoms and increased incidence of osteoarthritis later in life.4–13 The injury, surgery, and rehabilitation process usually keeps an athlete out of competition for up to 1 year. The psychological effects can be profound. Fear of reinjury and loss of confidence can be major factors precluding an athlete's return to play.5,14 The university athlete may also lose a year of school and possibly scholarship funding.

Multiple studies have demonstrated that these ACL injuries may be preventable.15–18 The implementation of NMT programs has been shown to be of potential benefit in reducing ACL injuries in female soccer players.15–18 However, recent research has shown that NMT programs can also be beneficial in reducing such injuries in male soccer players.19,20 In this article, we will examine ACL injury prevention and describe strategies that can deliver these programs to all Canadian youth soccer players.


Female athletes, including soccer players, have a 4 to 8 times greater risk than male athletes of sustaining a noncontact ACL injury in multidirectional sports.21–29 The reasons for this gender difference are likely multifactorial and may involve anatomical, hormonal, neuromuscular, and biomechanical differences.

Anatomical and Hormonal Risk Factors

Anatomical risk factors include a narrower intercondylar notch, smaller cross-sectional area of the ACL, and laxity of the knee joint.23,25,30–32 Sex hormones may also act directly on the ACL, potentially changing its tensile strength. Studies indicate that a higher number of ACL injuries occur in the follicular phase of the menstrual cycle, but the relationship between hormone levels, ligamentous laxity, and injuries is not well understood.33 Oral contraceptives may play a protective role in ACL injuries, but additional research is needed before hormonal manipulation can be recommended as a strategy for the prevention of injury.34–36

Neuromuscular and Biomechanical Risk Factors

Many studies have evaluated the differences in female and male athletes' movement patterns, strength, and proprioceptive abilities in an attempt to explain the higher incidence of noncontact ACL injuries in female athletes.21,37–45 Female athletes perform movements at high risk for ACL injury, such as cutting and landing from a jump, with decreased flexion and increased valgus angles at the knee. These positions of the knee may contribute to additional strain on the ACL and therefore an increased risk of injury.39,40,44 Prospective studies have identified deficits in core stability and control that were predictive of ACL injury in female but not male athletes.46,47 Women experience higher cumulative deterioration of their isokinetic leg strength associated with knee flexion after intermittent high-intensity exercise, an inherent demand in soccer. Therefore, an exercise program that focuses on neuromuscular control of the trunk, hip, and knee may decrease noncontact ACL injuries in women.41

An outcome from the Hunt Valley II Meeting on ACL injury prevention was identification of the various components that influence dynamic joint loading, including central nervous system control, nerve–muscle interaction, and muscle and joint factors.36 This consensus group recommended training proper technique in cutting and landing movements through such activities as gait training, agility drills, and plyometrics. The group also identified factors that may increase dynamic joint loading and strain on the ACL. These factors include fatigue, lowered torsional stiffness of the knee, muscle strength imbalance in the lower limb, unanticipated cutting or cutting, and landing with poor technique (ie, the knee in valgus). The group concluded that training can be used to reduce noncontact ACL injuries by modifying these components. For example, training exercises that improve the early recruitment and strength of the hamstring muscles may reduce anterior tibial translation and therefore reduce ACL strain during cutting activities and landing from a jump.36


Over the past decade, there has been conflicting evidence to support the effectiveness of NMT training programs in reducing the incidence of ACL injury.15–18,48–50 However, a series of meta-analyses now exist to support NMT programs. In 2006, Hewett et al51 reviewed 6 studies and found that balance training was not effective by itself but only when combined with other types of training. Grindstaff et al conducted a review of original research studies that compared NMT programs with control programs to determine the number of noncontact ACL injuries per event exposure or hours of playing time. Five studies met the inclusion criteria. The authors estimated the crude incidence rate ratio for intervention versus comparison groups to be 0.30 [95% confidence interval (CI), 0.26-0.61].52 In other words, a 70% reduction in the incidence of ACL injuries was observed in the NMT group compared with the control group.

Yoo et al22 evaluated the effectiveness of ACL injury prevention programs by performing a meta-analysis of 7 prospective cohort studies. Their study concluded that NMT prevention programs were effective at reducing the risk of ACL injury in female athletes. Training was more effective at decreasing ACL injury risk in subjects younger than 18 years of age and for subjects who played soccer compared to handball. Additionally, preseason and in-season training had higher injury prevention efficacy than either preseason or in-season training alone. Their analysis identified that plyometric, strengthening, and balance exercises are essential for a successful training program that can serve to prevent injuries and enhance performance.

A systematic literature review and meta-analysis authored in 2012 by Sadoghi et al sought to determine whether a particular NMT program offered superior protection when compared to other programs.19,20 The heterogeneity of the 14 NMT studies that were analyzed prevented the authors from choosing “the best” training program to prevent ACL injuries. However, all of the interventions that reduced ACL injuries had prevention programs that included exercises with a neuromuscular focus and were performed for at least 10 minutes, 3 times a week. Furthermore, their review provided strong evidence in support of ACL injury prevention program effectiveness, with a risk reduction of 52% in the female athletes and 85% in the male athletes.19,20 This meta-analysis supports our recommendation for NMT programs to be implemented across genders.

A 2012 systematic review and meta-analysis by Gagnier et al53 included 8 cohort (observational) studies and 6 randomized trials, involving a total of approximately 27 000 participants. The random-effects meta-analysis yielded a pooled rate-ratio estimate of 0.485 (95% CI, 0.299-0.788; P = 0.003), indicating a lower ACL injury rate in the intervention groups. However, there was appreciable heterogeneity of the estimated effect across studies. The authors found that various types of neuromuscular and educational interventions seem to reduce the incidence of ACL injuries by approximately 50%, but the estimated effect varied appreciably among studies.

In a meta-analysis that focused on female athletes, Myer et al54 suggested an optimal age window exists to maximize the positive effects of NMT programs in young female athletes. The authors found a 72% risk reduction in female athletes 18 years of age or younger, but only a 16% reduction for those older than 18 years. They concluded that the optimal time to initiate an NMT program is during early adolescence, before the changes in mechanics that increases injury risk occur.54


Fédération Internationale de Football Association (FIFA) is the international governing body of association football (soccer). Since 2003, FIFA has promoted injury prevention exercises. The 11+ exercises can be viewed at The “11+” was developed by a group of international experts from FIFA's Medical Assessment and Research Centre (F-MARC), the Oslo Sports Trauma Research Center, and the Santa Monica Sports Medicine Foundation.


Although the effectiveness of specific ACL injury prevention programs has been demonstrated, compliance and uptake of the programs may be a critical factor in decreasing ACL injuries overall.18,56 Finch56 suggests that athletes, coaches, and sports administrators will only adopt injury prevention strategies if certain criteria are met. They need to be convinced that the proposed strategies will actually prevent injuries, will not change the nature or enjoyment of the sport, will enhance rather than negatively affect performance, and are easy to do.56,57 Exercises are often designed as structured warm-up programs to ensure that all players use the program regularly.58 In youth soccer, coaches are often the decision makers regarding the implementation of injury prevention programs. Coaches are less likely to implement injury prevention programs if they are not soccer specific or take too much time away from regular practice.18 To be effective, ACL injury prevention training programs must accomplish 2 goals: (1) ameliorate known risk factors, and (2) be adopted by coaches and athletes and performed on a consistent and ongoing basis.

In Canada, the governing bodies for soccer include the Canadian Soccer Association (CSA) nationally and a provincial soccer association for each province. To be successful, the CSA and the provincial soccer associations must support an injury prevention program at the governance (board) level and at the technical (coaching) levels of administration. Such support should include an injury prevention component within the various coaching certification courses. This injury prevention component would provide the rationale and practical information on how to implement an injury prevention warm-up. The introduction of this training should be at the community level coaching courses and then would increase in detail and complexity in more advanced coaching courses. A “train the trainers” model would be employed, having a qualified health care professional deliver this module of the coaching program. The module would include practical demonstrations of the injury prevention exercises, a question and answer period, and DVDs and handouts demonstrating the same exercises for the coaches. Players could access this information on the CSA Web site where professional and national team players could be observed doing the program.

In a meta-analysis, Sugimoto et al59 found that the incidence of ACL injury was lower in studies with good compliance with NMT programs than in studies with poor compliance. To improve compliance, coaches need to be educated about the potential performance benefits, in addition to the effectiveness for injury prevention.58,60 Indeed, recent studies show that the coach is the key partner ensuring high player adherence to the program.61–63 In addition to injury prevention, Reis et al64 showed that the “11+” can be used as an effective conditioning means for improving physical fitness and technical performance of youth futsal (officially recognized as 5-a-side indoor soccer) players. Compliance will be further enhanced by ensuring that the programs delivered are time efficient (ie, included as part of the preexisting warm-ups), cost effective (ie, no additional equipment), and soccer specific.18,56 Team or group training remains the most feasible means of implementing injury prevention training, especially in youth sports. Qualified health care professionals can monitor teams for frequency, content, and quality of delivery of the programs on the field. They can also provide a resource for the coaches regarding questions, correction, and feedback. We recommend that the costs of implementing these programs be shared among the governing body, soccer leagues, and teams. An appendix is posted on the CASEM Web site and provides information regarding how 1 Canadian community has implemented a youth soccer NMT program. It is not yet clear which components of the current FIFA “11+” protocols are most effective at preventing ACL injuries. However, there is sufficient evidence for us to recommend that all Canadian youth soccer teams institute such training programs now.


The Canadian Academy of Sport and Exercise Medicine makes the following recommendations with respect to ways in which youth soccer players and their coaches can decrease the incidence of ACL injuries. The Table shows the definition of scoring recommendations, which are based on those reported by Ebell et al65

  1. All Canadian youth soccer players should engage in exercise programs that incorporate neuromuscular, proprioceptive, agility, and strength training in their routine practice and warm-ups (Strength of Recommendation = A).
  2. These NMT programs should be commenced at least by the early teenage years (Strength of Recommendation = A).
  3. During the performance of the ACL injury prevention program in training, the coaches and trainers should give effective feedback on the performance of the drills, and players should learn from watching each other perform the tasks (Strength of Recommendation = B).
  4. National and provincial soccer governing bodies should develop age-specific ACL injury prevention programs and monitor these programs for effectiveness based on the latest available evidence (Strength of Recommendation = B).
  5. Soccer teams should collaborate with a qualified health or physical education professional in the institution of an ACL injury prevention program for the team's training sessions (Strength of Recommendation = A).
  6. Professional organizations of sport medicine physicians, physiotherapists, chiropractors, athletic therapists, and physical education teachers can lead by encouraging their members to provide appropriate educational sessions and educational materials to soccer teams (Strength of Recommendation = C).
  7. Ongoing research to refine these programs according to the current evidence-based best training practices is essential (Strength of Recommendation = B).
  8. Ongoing understanding, development, and refinement of implementation strategies are needed to improve compliance and uptake of the prevention programs (Strength of Recommendation = A).
Strength of Recommendation Grades65


1. Silvers HJ, Mandelbaum BR. Prevention of anterior cruciate ligament injury in the female athlete. Br J Sports Med. 2007;41:i52–i59.
2. Boden BP, Dean GS, Feagin J, et al.. Mechanisms of anterior cruciate ligament injury. Orthopedics. 2000;23:573–578.
3. Krosshaug T, Nakamae A, Boden BP, et al.. Mechanisms of anterior cruciate ligament injury in basketball: video analysis of 39 cases. Am J Sports Med. 2007;35:359–367.
4. Laboute E, Savalli L, Puig P, et al.. Analysis of return to competition and repeat rupture for 298 anterior cruciate ligament reconstructions with patellar or hamstring tendon autograft in sportspeople. Ann Phys Rehabil Med. 2010;53:598–614.
5. Ageberg E, Forssblad M, Herbertsson P, et al.. Sex differences in patient-reported outcomes after anterior cruciate ligament reconstruction: data from the Swedish knee ligament register. Am J Sports Med. 2010;38:1334–1342.
6. Keays SL, Newcombe PA, Bullock-Saxton JE, et al.. Factors involved in the development of osteoarthritis after anterior cruciate ligament surgery. Am J Sports Med. 2010;38:455–463.
7. Neuman P, Englund M, Kostogiannis I, et al.. Prevalence of tibiofemoral osteoarthritis 15 years after nonoperative treatment of anterior cruciate ligament injury: a prospective cohort study. Am J Sports Med. 2008;36:1717–1725.
8. Renstrom P, Ljungqvist A, Arendt E, et al.. Non-contact ACL injuries in female athletes: an International Olympic Committee current concepts statement. Br J Sports Med. 2008;42:394–412.
9. Lohmander LS, Englund PM, Dahl LL, et al.. The long-term consequence of anterior cruciate ligament and meniscus injuries: osteoarthritis. Am J Sports Med. 2007;35:1756–1769.
10. Freedman KB, Glasgow MT, Glasgow SG, et al.. Anterior cruciate ligament injury and reconstruction among university students. Clin Orthop Relat Res. 1998;356:208–212.
11. Podlog L, Eklund R. Assisting injured athletes with the return to sport transition. Clin J Sport Med. 2004;14:257–259.
12. Soderman K, Pietila T, Alfredson H, et al.. Anterior cruciate ligament injuries in young females playing soccer at senior levels. Scand J Med Sci Sports. 2002;12:65–68.
13. Lohmander LS, Ostenberg A, Englund M, et al.. High prevalence of knee osteoarthritis, pain and functional limitation in female soccer players twelve years after anterior cruciate ligament injury. Arthritis Rheum. 2004;50:3145–3152.
14. Langford JL, Webster KE, Feller JA. A prospective longitudinal study to assess psychological changes following anterior cruciate ligament reconstruction surgery. Br J Sports Med. 2009;43:377–378.
15. Myklebust G, Engebretsen L, Braekken IH, et al.. Prevention of anterior cruciate ligament injuries in female team handball players: a prospective intervention study over three seasons. Clin J Sport Med. 2003;13:71–78.
16. 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. Am J Sports Med. 2005;33:1003–1010.
17. Walden M, Atroshi I, Magnusson H, et al.. Prevention of acute knee injuries in adolescent female football players: cluster randomised controlled trial. Br J Sports Med. 2012;46:904.
18. Soligard T, Nilstad A, Steffen K, et al.. Compliance with a comprehensive warm-up programme to prevent injuries in youth football. Br J Sports Med. 2010;44:787–793.
19. Sadoghi P, Von Keudell A, Vavken P. Effectiveness of anterior cruciate ligament injury prevention training programs. J Bone Joint Surg Am. 2012;94:769–776.
20. Wright RW. An ounce of prevention beats a pound of reconstruction. Commentary on an article by Patrick Sadoghi, MD, et al: “Effectiveness of anterior cruciate ligament injury prevention training programs”. J Bone Joint Surg Am. 2012;94:e60.
21. Boden BP, Sheehan FT, Torg JS, et al.. Noncontact anterior cruciate ligament injuries: mechanisms and risk factors. J Am Acad Orthop Surg. 2010;18:520–527.
22. Yoo JH, Lim BO, Ha M, et al.. A meta-analysis of the effect of neuromuscular training on the prevention of the anterior cruciate ligament injury in female athletes. Knee Surg Sports Traumatol Arthrosc. 2010;18:824–830.
23. Myer GD, Ford KR, Paterno MV, et al.. The effects of generalized joint laxity on risk of anterior cruciate ligament injury in young female athletes. Am J Sports Med. 2008;36:1073–1080.
24. Hewett TE, Lindenfeld TN, Riccobene JV, et al.. The effect of neuromuscular training on the incidence of knee injury in female athletes. A prospective study. Am J Sports Med. 1999;27:699–706.
25. Arendt E, Dick R. Knee injury patterns among men and women in collegiate basketball and soccer: NCAA data and review of literature. Am J Sports Med. 1995;23:694–701.
26. Harmon KG, Ireland ML. Gender differences in noncontact anterior cruciate ligament injuries. Clin Sports Med. 2000;19:287–302.
27. Ireland ML. The female ACL: why is it more prone to injury? Orthop Clin North Am. 2002;33:637–651.
28. Emery CA, Meeuwisse WH, Hartmann SE. Evaluation of risk factors for injury in adolescent soccer: implementation and validation of an injury surveillance system. Am J Sports Med. 2005;33:1882–1891.
29. Shea KG, Pfeiffer R, Wang JH, et al.. Anterior cruciate ligament injury in pediatric and adolescent soccer players: an analysis of insurance data. J Pediatr Orthop. 2004;24:623–628.
30. Shelbourne KD, Davis TJ, Klootwyk T. The relationship between intercondylar notch width of the femur and the incidence of anterior cruciate ligament tears. Am J Sports Med. 1998;26:402–408.
31. Muneta T, Takakuda K, Yamamoto H. Intercondylar notch width and its relation to the configuration and cross-sectional area of the anterior cruciate ligament: a cadaveric knee study. Am J Sports Med. 1997;25:69–72.
32. Medrano D, Smith D. A comparison of knee joint laxity among male and female collegiate soccer players and non-athletes. Sports Biomecha. 2003;2:203–212.
33. Shultz SJ, Sander TC, Kirk SE, et al.. Sex differences in knee joint laxity change across the female menstrual cycle. J Sports Med Phys Fitness. 2005;45:594–603.
34. Lebrun CM, Joyce SM, Constantini NW. Effects of female reproductive hormones on sports performance. In: Constantini NW, Hackney AC, eds. Endocrinology of Physical Activity and Sport. 2nd ed. Totowa, NJ: The Humana Press; 2013:281–322.
35. Martineau PA, Al-Jassir F, Lenczner E, et al.. Effect of the oral contraceptive pill on ligamentous laxity. Clin J Sport Med. 2004;14:281–286.
36. Griffin LY, Albohm MJ, Arendt EA, et al.. Understanding and preventing noncontact anterior cruciate ligament injuries: a review of the Hunt Valley II meeting, January 2005. Am J Sports Med. 2006;34:1512–1532.
37. Powell JW, Barber-Foss KD. Sex-related injury patterns among selected high school sports. Am J Sports Med. 2000;28:385–391.
38. Rozzi SL, Lephart SM, Gear WS, et al.. Knee joint laxity and neuromuscular characteristics of male and female soccer and basketball players. Am J Sports Med. 1999;27:312–319.
39. Malinzak R, Cobby S, Kirkendall D, et al.. A comparison of knee motion and electromyography patterns between men and women in selected athletic manoeuvres. Clin Biomech (Bristol, Avon). 2001;16:438–445.
40. Ford K, Myer GD, Hewett TE. Valgus knee motion during landing in high school female and male basketball players. Med Sci Sports Exerc. 2003;35:1745–1750.
41. Mercer TH, Gleeson NP, Wren K. Influence of prolonged intermittent high-intensity exercise on knee flexor strength in male and female soccer players. Eur J Appl Physiol. 2003;89:506–508.
42. Caraffa A, Cerulli G, Projetti M, et al.. Prevention of anterior cruciate injuries in soccer: a prospective controlled study of proprioceptive training. Knee Surg Sports Traumatol Arthrosc. 1996;4:19–21.
43. McLean SG, Beaulieu ML. Complex integrative morphological and mechanical contributions to ACL injury risk. Exerc Sport Sci Rev. 2010;38:192–200.
44. Yu B, Kirkendall DT, Garrett WE. Anterior cruciate ligament injuries in female athletes: anatomy, physiology and motor control. Sports Med Arthrosc Rev. 2002;10:58–68.
45. Urabe Y, Kobayashi R, Sumida S, et al.. Electromyographic analysis of the knee during jump landing in male and female athletes. Knee. 2005;12:129–134.
46. Zazulak BT, Hewett TE, Reeves NP, et al.. Deficits in neuromuscular control of the trunk predict knee injury risk: a prospective biomechanical-epidemiologic study. Am J Sports Med. 2007;35:1123–1130.
47. Zazulak BT, Hewett TE, Reeves NP, et al.. The effects of core proprioception on knee injury: a prospective biomechanical-epidemiological study. Am J Sports Med. 2007;35:368–373.
48. Heidt RS, Sweeterman LM, Carlonas RL, et al.. Avoidance of soccer injuries with preseason conditioning. Am J Sports Med. 2000;28:659–662.
49. Soderman K, Werner S, Pietila T, et al.. Balance board training: prevention of traumatic injuries of the lower extremities in female soccer players? A prospective randomized intervention study. Knee Surg Sports Traumatol Arthrosc. 2000;8:356–363.
50. Pfeiffer RP, Shea KG, Roberts D, et al.. Lack of effect of a knee ligament injury prevention program on the incidence of non contact anterior ligament injury. J Bone Joint Surg Am. 2006;88:1769–1774.
51. 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. Am J Sports Med. 2006;34:490–498.
52. Grindstaff TL, Hammill RR, Tuzson AE, et al.. Neuromuscular control training programs and non-contact anterior cruciate ligament injury rates in female athletes: a numbers-needed-to-treat analysis. J Athl Train. 2006;41:450–456.
53. Gagnier JJ, Morgenstern H, Chess L. Interventions designed to prevent anterior cruciate ligament injuries in adolescents and adults. A systematic review and meta-analysis. Am J Sports Med. 2013;41:1952–1962.
54. Myer GD, Sugimoto D, Thomas S, et al.. The influence of age on the effectiveness of neuromuscular training to reduce anterior cruciate ligament injury in female athletes: a meta-analysis. Am J Sports Med. 2013;41:203–215.
55. F-MARC. 11+ (Fédération Internationale de Football Association [FIFA] Web site). Accessed April 15, 2013.
56. Finch C. A new framework for research leading to sports injury prevention. J Sci Med Sport. 2006;9:3–9.
57. Eime R, Owen N, Finch C. Protective eyewear promotion: applying principles of behaviour change in the design of a squash injury prevention programme. Sports Med. 2004;34:629–638.
58. Steffen K, Bahr R, Myklebust G. ACL prevention in female football. Aspetar Sports Med J. 2013;2:178–185.
59. Sugimoto D, Myer GD, Bush HM, et al.. Compliance with neuromuscular training and anterior cruciate ligament injury risk reduction in female athletes: a meta-analysis. J Athl Train. 2012;47:714–723.
60. Postma WF, West RV. Anterior cruciate ligament injury prevention programs. J Bone Joint Surg Am. 2013;95:661–669.
61. Steffen K, Emery CA, Romiti M, et al.. High adherence to a neuromuscular injury prevention programme (FIFA 11+) improves functional balance and reduces injury risk in Canadian youth female football players: a cluster randomized trial. Br J Sports Med. 2013;47:794–802.
62. Steffen K, Meeuwisse WH, Romiti M, et al.. Evaluation of how different implementation strategies of an injury prevention programme (FIFA 11+) impact team adherence and injury risk in Canadian female youth football players: a cluster randomized trial. Br J Sports Med. 2013;47:480–487.
63. Myklebust G, Skjolberg A, Bahr R. ACL injury incidence in female handball 10 years after the Norwegian ACL prevention study: important lessons learned. Br J Sports Med. 2013;47:476–479.
64. Reis I, Rebelo A, Krustrup P, et al.. Performance enhancement effects of Federation Internationale de Football Association's “The 11+” injury prevention training program in youth futsal players. Clin J Sport Med. 2013;23:318–320.
65. Ebell MH, Siwek J, Weiss BD, et al.. Strength of recommendation taxonomy (SORT): a patient-centered approach to grading evidence in the medical literature. J Am Board Fam Pract. 2004;17:59–67.
© 2014 by Lippincott Williams & Wilkins