One of the ongoing mysteries of sports medicine is why women athletes suffer so many more anterior cruciate ligament (ACL) injuries than men. The ACL is a ligament in the knee that is commonly injured during stop-and-go running, cutting, and jumping during sports. Basketball, soccer, and volleyball players are especially prone to ACL tears. Recovery from ACL tears can be difficult. They sometimes end the sports careers of athletes. Women athletes would work hard to prevent ACL tears–if only they knew how.
These authors wanted to test the idea that women athletes can’t consciously activate the knee muscles to the same extent as men. Men and women basketball, volleyball, and soccer players from Division I athletic programs were recruited for the study. So were men and women athletes who bicycled, rowed, and ran. This group was included to see how the knee muscles worked in athletes who didn’t put such high demands on their ACLs.
All the athletes sat with their knees bent at 30 degrees and then again at 60 degrees. A machine put a certain amount of force on the outside of the foot. This mimics the forces on the knee when landing from a jump on one foot. Knee and leg movements and muscle activation were measured while the athletes were passive. Measurements were taken again while the athletes resisted the force with all their might.
Results showed that the women’s knees rotated much more than the men’s knees. Also, men increased their knee stiffness significantly more than women did when they were told to resist the force (218 percent for men compared to 178 percent for women). All athletes had less knee rotation when the knee was bent to 60 degrees. For the most part, athletes who took part in bicycling, rowing, and running had more knee rotation and less knee stiffness than the basketball, soccer, and volleyball players.
Surprisingly, the women basketball, soccer, and volleyball players showed the least amount of increase in knee stiffness between the passive and active tests. The women’s knee muscles seemed to be fully activated, but they could not generate the same increase in knee stiffness. The authors don’t know why this is true, but they believe this leads to less muscle protection around the knee and may play a role in why women have more ACL injuries.
Further research with more athletes is needed to make complete sense of this mystery. However, this study does point to some new directions for training and strengthening programs for women basketball, volleyball, and soccer players.