The anterior cruciate ligament (ACL) of the knee is up to eight times more likely to be injured in women athletes than in men. No one knows exactly why this is true, although many factors have been tested–everything from increased joint laxity and weaker thigh muscles, to hormones and inadequate shoes. Many of these factors may be involved, but none has been identified as the primary cause of increased ACL injuries in women.
These authors tested the role of the hip muscles. Nine male and nine female Division I college athletes did single-leg squats. Single-leg squats were chosen because the movement is common in sports and it requires body control on a fixed leg. Electrodes over the thigh muscles were used to measure the athletes’ muscle activation, while cameras recorded the movements.
There was a great deal of difference in the way men and women did the squats. Women tended to further bend their ankles, tilt their feet inward, bend at the hips, and rotate the hips out. Women also tended to start and end the squat a bit bowlegged, which the men never did. The women also activated their quadriceps muscles (in the front of the thigh) more than the men.
The authors thought the results suggest that women have a harder time controlling the muscles of the hips, so they rely more on the quadriceps muscles to control the knee. This puts the knee in a less stable position, which could help explain why women are more prone to ACL injuries.
The results were not conclusive, but the authors believe they are onto something. They are doing follow-up studies with more athletes to determine how differences in hip muscles affect women’s chances of ACL injury.