Introduction
In all sports, injury is common. As such, scientists and medical health professionals have taken painstaking measures to research how injuries might be prevented—or at least how the risk of injury might be reduced therein. Female athletes, in particular, are considered to be more prone to lower limb injuries than male athletes, mostly due to anatomical variance. With this in mind, much research has been devoted to anterior cruciate ligament (ACL) injury prevention among the female athletic population.
The following annotated bibliography identifies several compelling research studies focusing on ACL and lower ligament injury prevention among this population. Each study advocates on behalf of neuromuscular interventions as a valid mechanism for injury prevention in female athletes.
Statement of Research Question
Is neuromuscular training effective in preventing non-contact ACL injuries among female athletes?
Annotated Bibliography
1. Hewett, T. E., Ford, K. R., & Myer, G. D. (2006; 2005). Anterior cruciate ligament injuries in female athletes: Part 2, a meta-analysis of neuromuscular interventions aimed at injury prevention. The American Journal of Sports Medicine, 34(3), 490-498. doi:10.1177/0363546505282619
The purpose of this study was to determine whether or not neuromuscular training programs would reduce the risk of anterior cruciate ligament (ACL) injuries among female athletes. The authors, who were medical professionals from Ohio medical and research facilities, performed a literature search looking for studies that were either randomized control trials or prospective cohort studies, as well as studies that sought the prevention of ACL injuries through neuromuscular training. A meta-analysis was performed of six studies.
The first study included female basketball, soccer, and volleyball players, and the intervention group performed neuromuscular training three times a week. The risk of
ACL injuries was reduced by 72 percent. The second study was among high school female soccer players only, and their intervention group was enrolled in neuromuscular training. This involved treadmill speed training twice a week and agility sessions seven times prior to the season. Although there were less overall injuries, there was no difference between the control group and the intervention group in ACL injuries. The third study was a randomized control trial of female soccer players, and there was no significant difference in ACL injuries between the two groups. This may have been because of the low number of subjects or poor compliance due to some exercises being performed at home. The fourth study evaluated female handball players over three seasons, the second where neuromuscular training was implemented. There was a 36 percent decrease in the risk of ACL injury. A controlled cohort study of female soccer players reported significant results of neuromuscular training in a fifth study as did a sixth controlled study of German handball players.
Limitations to these studies include small subject numbers (too small to support the null hypothesis), underreporting and poor compliance. However, this literature review suggests that neuromuscular training does provide ACL protection through plyometrics, biometric evaluation and feedback, balance and core training, and strength training.
2. Khuu, S., Musalem, L. L., & Beach, T. A. C. (2015). Verbal instructions acutely affect drop vertical jump Biomechanics—Implications for athletic performance and injury risk assessments. Journal of Strength and Conditioning Research, 29(10), 2816-2826.
doi:10.1519/JSC.0000000000000938
This study was performed by Faculty of Kinesiology and Physical Education in
Ontario, Canada. Ten women and ten men volunteered to be a part of this study in an attempt to determine whether or not verbal instruction had an impact on drop vertical jumps (DVJs). These exercises are often used in injury risk assessment and in evaluating performance potential in athletes. Each subject was asked to participate in a one-hour training session. They were allowed a 10-minute warmup and 5 practice DVJs. Then, they performed three sets of 5 maximum-effort DVJs with different verbal instruction.
The instructions were to minimize ground contact time, maximize jump height and to extend the lower extremity joints synchronously. While there were no statistical differences between the last two instructions, there were individual differences. The instruction to minimize ground contact time led to stiffer landings, which could create false reporting of injury risk. This study is relevant in the risk assessment of athletes. For example, if there is an uncontrolled frontal plane knee motion during DVJs, that athlete is then considered more at risk for ACL tears.
3. Myer, G. D., Ford, K. R., Palumbo, J. P., & Hewett, T. E. (2005). Neuromuscular training improves performance and lower-extremity biomechanics in female athletes. Journal of Strength and Conditioning Research, 19(1), 51-60. Retrieved from https://search-proquestcom.contentproxy.phoenix.edu/docview/213074456?accountid=134061
This study evaluated 41 female sports players in a six-week training session where the intervention group was given neuromuscular training. It was an attempt to examine the effects of neuromuscular training and whether or not it would improve performance along with biomechanics, thus reducing the lower extremity injury risk among female athletes. The hypothesis of the research was that neuromuscular training would increase performance and biomechanics, which would result in a lowered risk for ACL injuries.
A six-week training event included plyometric movement, strengthening and balance, resistance training and speed training exercises, and the control groups were matched with intervention groups for height and weight. The results were significant and showed that comprehensive neuromuscular training can improve performance and reduce injury when it is designed for the prevention of lower-limb injuries. It does this through the improvement of biomechanics. This is significant because the sample fits the demographic of the research in question, and it shows significant results. It is also significant because it stresses the importance of biomechanics.
4. Myer, G. D., Ford, K. R., McLean, S. G., & Hewett, T. E. (2006; 2005). The effects of plyometric versus dynamic stabilization and balance training on lower extremity biomechanics. The American Journal of Sports Medicine, 34(3), 445-455. doi:10.1177/0363546505281241
A study of 23 female high school volleyball players determined that comprehensive neuromuscular training decreases the risk of non-contact ACL injuries among female athletes, who are 4 to 6 times more likely to get those injuries than male athletes. The authors were PhD and master’s graduates working in Ohio research facilities, and the research was funded by a grant from the National Institutes of Health.
First, the study determined that 18 subjects were needed to achieve clinically relevant results. They did this by acquiring kinematic data from female athletes who were both ACL-injured and ACL-non-injured. Following this determination, two teams were created among the 23 athletes. One group participated in plyometric training, and the second group participated in dynamic stabilization and balance training.
Statistically significant effects were observed, but it could not be determined if these were irrespective from other training the participants engaged in, such as resistance, speed and agility training. This study is limited by the fact that there were only two training protocols, and further testing would be necessary to determine how significant each protocol was. However, this study was relevant to coaches and sports trainers because it showed significant improvement in ACL injuries among female athletes when subjected to comprehensive neuromuscular training.
5. Panariello, R. A., Stump, T. J., & Cordasco, F. A. (2017). The lower extremity athlete: Postrehabilitation performance and injury prevention training. Operative Techniques in Sports Medicine, 25(3), 231. doi:10.1053/j.otsm.2017.07.011
One of the last articles was about injury prevention post-ACL surgery among athletes. It focused on post-surgery rehabilitation and performance enhancement. The authors of the report were medical professionals from Professional Orthopedic and Sports Physical
Therapy along with other professional orthopedic health organizations. This report is relevant because of the intention to speed up recovery from ACL surgeries, which can take up to one year before an athlete is able to return to their pre-injury ability.
The report focuses on physical qualities (PQ), which are unrelated to skill level in sports. Physical qualities are considered to be essential to rehabilitation. Hall of Fame coach, Al Vermeil, created an accepted hierarchy of physical qualities, which he used to win multiple world championships. The pyramid has speed at the top, or the smallest part of the pyramid. This is followed by elastic/reactive strength, explosive strength, strength, work capacity and evaluation/testing.
This is relevant to female athletes because once an ACL repair is performed, they must be able to rehabilitate physical qualities to return to sport, or they risk re-injury. The limitations of this report are that it does not consider any other methods but Mr. Vermeil’s, and it does not focus on prevention.
6. Stevenson, J. H., Beattie, C. S., Schwartz, J. B., & Busconi, B. D. (2015). Assessing the effectiveness of neuromuscular training programs in reducing the incidence of anterior cruciate ligament injuries in female athletes: A systematic review. The American Journal of Sports Medicine, 43(2), 482-490. doi:10.1177/0363546514523388
The final study was a systematic review of 10 articles (pared down from 1,976 articles) by two independent reviewers who are fellowship trained sports medicine physicians from the University of Massachusetts Medical Center. The goals of the study were to build off of previous reviews, including the 2015 study by Hewett et al. The study aimed to find evidence-based support for neuromuscular training programs to prevent ACL injuries among females. It also rated the qualities of the articles.
The review included only prospective cohort studies and randomized control trials because of the author’s believe that there are too many limitations in other forms of studies. The authors rated the articles based on a modified Downs and Black criteria, in which the articles rated 14.5 to 16.5 out of a possible 26 points.
Plyometrics was used in 80 percent of the studies. Strength training was used in 60 percent of the studies. Flexibility was used in 40 percent of the studies, and three articles incorporated balance training only. Once again, the evidence was not very significant in support of neuromuscular training programs. Only two studies found a statistically significant decrease in ACL injuries as a result of the programs.
Limitations of this study are small group sizes (less than 1000 in all but one study), only 3 randomized control trials and lack of information about age, race, weight and other personal factors that could be significant. Five of the studies also did not distinguish between contact and non-contact ACL injuries.
The final results of the systematic review of 10 articles concluded that there is moderate evidence that neuromuscular training can reduce ACL injuries in female athletes when it involves preseason conditioning and plyometrics. There is also moderate evidence that when only utilized in-season, it does not reduce injury. Only using plyometrics did not result in significant reduction in ACL injuries, and confounding variables limited definitive answers to the questionable effectiveness of neuromuscular training programs.
Overall, this study relates to the chosen topic perfectly, and it is performed by physicians at a reputable medical center. It effectively rates and assesses previous studies, but it does not provide clear evidence in support of neuromuscular training programs as an effective measure to prevent ACL injuries in women.
Clinical Implications
The results of the six previous studies will impact my clinical practice, as it will not support an approach to ACL injury prevention among female athletes by neuromuscular training programs. However, it does not exactly discourage it either. In addition, there is minimal risk involved in implementing neuromuscular training, and the cost is minimal, so it may be better suited for certain cases. The biggest cost is time, and this will have to be a consideration for coaches and individuals who may not comply with time requirements without clear evidence that the preventive measure is effective.
Still, with the minimal risk, this is a preventive measure that I will consider on a case-by-case basis when the patient seems to be willing to comply with the training, and the minimal risk and cost advocates for support of the method. Essentially, it is one tool that has shown to help some individuals, but it cannot be relied upon to prevent ACL injuries among female athletes. Another consideration is when and how to use neuromuscular training programs. It appears that pre-season utilization does help female athletes to prevent ACL injury, but there is no evidence to support only in-season use of the program. Additionally, only using plyometrics was not a conclusive prevention strategy, but multi-faceted training programs that include pre-season use appear to be more beneficial.
Conclusion
It is clear by these studies that ACL injury among female athletes is a relevant problem— and certainly worth studying the prevention and rehabilitation of due to the increased risk among this population when compared to that of the male population. Not only are women two to eight times more likely to get an ACL injury, but most of them are non-contact so feasibly preventable. The body habitus of females leads to an increased risk for ACL injuries due to small joints, wider hips, increased joint laxity and different patterns of movement. The increased involvement of women in the sports arena has created a call for action in regard to preventing these injuries, which can cause long-term disability. The effects of ACL injuries, because of the length of recovery time, can lead to low self-esteem, isolation, loss of scholarship and delay returning to sports, which increases opportunities for females.
The studies clearly show that neuromuscular training can aid in the prevention of ACL injuries and can enhance physical performance among female athletes. Limitations to this literature review are that neuromuscular interventions are not all similar, and the subjects of all studies come from different sports. In order for research to increase relevancy, each sport much show similar results, and the interventions should be standardized. However, the current literature supports the hypothesis that neuromuscular training is a moderately valid strategy for reducing ACL injuries among female athletes.
Future Research
In order to get statistically relevant research on the subject of ACL injuries among female athletes, research needs to become larger and more specified. There need to be more controls such as specifying sport, re-injury rates, and how the ACL injury happened (contact vs. non-contact). In addition, body characteristics should be considered, such as age, race and weight. One of the biggest difficulties in study design is ensuring compliance, and some studies use self-reported compliance, which is unreliable. Studies must include coaches and training staff who can ensure training is being implemented. The lack of strong support for neuromuscular training programs seems to be due to study design, and honing the variables measured and considered in these studies could result in more support for this method in order to prevent ACL injuries among female athletes.
- Hewett, T. E., Ford, K. R., & Myer, G. D. (2006;2005;). Anterior cruciate ligament injuries in female athletes: Part 2, a meta-analysis of neuromuscular interventions aimed at injury prevention. The American Journal of Sports Medicine, 34(3), 490-498.doi:10.1177/0363546505282619
- Khuu, S., Musalem, L. L., & Beach, T. A. C. (2015). Verbal instructions acutely affect drop vertical jump Biomechanics—Implications for athletic performance and injury risk assessments. Journal of Strength and Conditioning Research, 29(10), 2816-2826. doi:10.1519/JSC.0000000000000938
- Myer, G. D., Ford, K. R., Palumbo, J. P., & Hewett, T. E. (2005). Neuromuscular training improves performance and lower-extremity biomechanics in female athletes. Journal of Strength and Conditioning Research, 19(1), 51-60. Retrieved from https://searchproquest-com.contentproxy.phoenix.edu/docview/213074456?accountid=134061
- Myer, G. D., Ford, K. R., McLean, S. G., & Hewett, T. E. (2006;2005;). The effects of plyometric versus dynamic stabilization and balance training on lower extremity biomechanics. The American Journal of Sports Medicine, 34(3), 445-455. doi:10.1177/0363546505281241
- Panariello, R. A., Stump, T. J., & Cordasco, F. A. (2017). The lower extremity athlete: Postrehabilitation performance and injury prevention training. Operative Techniques in Sports Medicine, 25(3), 231. doi:10.1053/j.otsm.2017.07.011
- Stevenson, J. H., Beattie, C. S., Schwartz, J. B., & Busconi, B. D. (2015). Assessing the effectiveness of neuromuscular training programs in reducing the incidence of anterior cruciate ligament injuries in female athletes: A systematic review. The American Journal of Sports Medicine, 43(2), 482-490. doi:10.1177/0363546514523388
