Anterior cruciate ligament (ACL) injuries are on the rise, with about 350,000 patients undergoing ACL reconstruction surgery in the U.S. each year — and young athletes being the fastest growing patient population. Despite advances in ACL reconstruction, the risks of re-tear and future osteoarthritis are still major areas of concern. With this in mind, many institutions have increased clinical and research efforts for ACL injury prevention — a significant area of focus for The Micheli Center for Sports Injury Prevention at Boston Children’s Hospital.
Dai Sugimoto, PhD, ATC, CSCS, director of Clinical Research at The Micheli Center (TMC), has recently published research showing significant evidence for the efficacy of specific ACL injury prevention exercises in certain female athletes. When performed for just 20 minutes, two times per week, during the athletic season, these neuromuscular training (NMT) exercises reduced the risk of sustaining an ACL injury.
Increased risk in female athletes
The occurrence of ACL injuries in young female athletes is two to four times higher in cutting, jumping and pivoting sports compared to males. This is due to a number of factors, including differences in flexibility and strength between the two genders. “If you compare how males grow, they get a lot more muscular strength while they are going through puberty,” explains Sugimoto. “Females do not gain as much strength in their lower extremities, especially their hips.” This can lead to a higher incidence of ACL injuries for young female athletes.
In his research, Sugimoto wanted to focus on exercises that strengthen the hip and hamstring, as well as increase core strength. He hypothesized that this helps control movement and ultimately reduces a female athlete’s risk of ACL injuries.
What is NMT?
For these exercises, NMT assists with controlling the amount of external loading at the knee joint by improving muscular support and emphasizing proper athletic techniques. NMT can be classified into four different areas: balance, plyometrics, strengthening, and proximal control training. The goal is to enhance biomechanical and neuromuscular control through this training in order to help support a better quality of movements in cutting, jumping and pivoting movements. NMT includes exercises such as Russian/Nordic hamstring curls, single leg squats and planks — among many others.
Since the 1990s, 16 large-scale clinical trials have been published to test the efficacy of NMT on reducing ACL injuries in female athletes. From these prior studies and additional analysis, Sugimoto has put together a research-based strategy for female clients at The Micheli Center, who are looking to decrease their risk of ACL injury or reduce chances of re-injury for athletes that have already undergone ACL reconstruction.
Who should be doing these exercises?
Complying and adhering to NMT is crucial for the success of decreasing ACL injury risk
NMT has been shown to be significantly effective in helping prevent ACL injuries in female soccer and handball players and shows promise for being effective for basketball players as well. Evidence also shows that younger athletes have better outcomes from NMT than older athletes. Specifically, female athletes 14-18 years old and 19-20 years old showed a reduced risk of sustaining ACL injuries by 72 percent and 52 percent, respectively. Therefore, it makes the most sense for athletes to begin NMT when they are in their early teens.
Why are some athletes more prone to ACL injuries?
There are a number of biomechanical factors that contribute to an athlete’s risk of noncontact ACL injuries. A prospective study that looked at modifiable risk factors in female high-school soccer and basketball players reported that athletes who sustained non-contact ACL injuries were more likely to have the following:
- increased knee abduction (so called “valgus”) moments
- limited knee flexion angles
- greater ground reaction force (GRF)
- asymmetrical landing patterns
Of these four risk factors, increased knee abduction was the strongest indicator of a greater risk of ACL injury. Other studies have identified increased lateral trunk flexion angles and deficits in trunk control as a risk factor for ACL injury in female collegiate athletes as well.
How does NMT help?
Sugimoto found studies that include strengthening and proximal control (hamstrings, hip, and trunk control) are effective in reducing risk of ACL injury. In addition to strength and proximal control training, a few studies identified beneficial effects of plyometric exercises, which help reduce GRF with landing.
Another study indicated that those who have high GRF also tend to have increased knee abduction moments and decreased knee flexion in landing. To alter these biomechanical cascades, Sugimoto theorized that developing sufficient strength to attenuate GRF and sound control of proximal segments (hip and trunk) are crucial.
Other important findings:
- Complying and adhering to NMT is crucial for the success of decreasing ACL injury risk, as higher compliance rates are associated with decreased incidence of ACL injuries.
- The duration and frequency of NMT sessions were directly associated with ACL injury reduction. The more time athletes spend performing NMT, the fewer ACL injuries they sustain.
- NMT that incorporates multiple types of exercises was found to result in a greater reduction of ACL injury when compared to NMT with only a single exercise (i.e. only doing plyometrics, resistance training, or balance training).
- Verbal feedback and video instruction have been shown to increase the benefits of NMT, so it is highly recommended that athletes are provided with a feedback system incorporating verbal cues while performing NMT.
In short, these exercises are only effective if they are used consistently and accurately with young female athletes. If coaches and athletic trainers want to reduce the risk of ACL injury for female athletes in these sports, there is clear evidence that NMT is an effective preventative measure.
Sugimoto plans to continue evaluating the effectiveness of NMT in other sports that have a high risk of ACL injury, such as basketball, as well as take a closer look at how the young male athlete population can also reduce their risk of ACL injury. For now, The Micheli Center continues to implement these exercises with athletes looking to reduce their risk of ACL injury, and it has seen great results.
Learn more about the ACL Program at Boston Children’s Hospital