Approximately 80% of ACL tears occur without any physical contact with another player. Instead, the tear happens when a player lands from a jump, decelerating suddenly, or quickly changing direction. Since these actions are so common in soccer and basketball, it’s those players that are the most at-risk. And female athletes have the greatest risk of ACL injuries, with rates 4 to 6 times as high as for their male counterparts in the same sports. While ACL injuries are uncommon among younger players, the rate starts to pick up once girls turn 12.
Why are female athletes at such high risk? Researchers from the University of Akron and Akron Children’s Hospital have discovered differences between genders in the way information is translated from genes that lead to proteins responsible for maintaining ligament structure. This gender difference in gene expression “may account for weaker ACLs in females than males,” the researchers concluded in an abstract describing their findings. According to Contemporary Pediatrics, biomechanical studies have identified four neuromuscular issues that are more common in girls and could put their ACL at a high risk of tearing.
1. Girls tend to use their quadriceps muscles much more than their hamstrings for power. During a jump landing or quick change in direction, girls have reduced knee flexion, increased quadriceps activity, and decreased hamstring activity compared with boys. This “quadriceps dominant” strategy has been shown to increase both anterior tibial translation and strain on the ACL, making it more prone to tears.
2. Girls tend to have one leg that is stronger than the other, whereas boys tend to have equal strength in both legs. Asymmetry in leg strength promotes asymmetric weight distribution between an athlete’s feet upon landing from a jump (as they favor the stronger leg), causing a shift of the body’s center of mass away from its base of support, putting more pressure on the ligaments.
3. Girls tend to naturally have less core strength and stability, which makes it more difficult for them to control their center of mass and prevent it from shifting away from their base of support.
4. Girls tend to rely on bones and ligaments to stop joint motion, rather than contracting their muscles to control joint position and absorb the landing forces.
And even though many athletes heal from a torn ACL and continue on with their athletic careers, osteoarthritis of the knee has been shown to develop in 50% to 100% of injured female athletes within one to two decades after injury.
So what’s a female athlete, especially a soccer or basketball player, to do?
Coaches and parents of female athletes should invest in a training program designed to improve strength, flexibility, and coordination, as well as to counteract incorrect existing movements and lessen stress on the knee. This would mean focusing on exercises that strengthen the hamstring and core muscles, and retraining female athletes how to position/hold their knee while playing. A combination of strength training and plyometrics gives female athletes the strength they need in the places they need it to best protect their ACL.