Every year an estimated 38,000 young women tear their A.C.L.s in non-contact sports - a rate much higher than male athletes. That led researchers to believe that differences between male and female anatomy, hormones or neuromuscular control could be responsible for the problem.
Doctor AJit Chaudhari of the Ohio State University's Sports Medicine Center looked at one of the most basic differences between the sexes. He tested women's knees at different stages during their menstral cycles. Two earlier studies suggested a woman's hormones might explain why they're injured more often, but Chaudhari's study found that's not a factor.
Instead, he says, "what we found in the study was actually that there were no differences in men and women in terms of the load on their hip and their knee when they did various high-risk activities."
By ruling out the menstrual cycle, researchers can focus their attention on other explanations - and they're doing so with a sense of urgency. When women tear A.C.Ls at an early age, they're much more likely develop osteoarthritis - some get it in their 20's. Experts say stretching and programs specifically designed to strengthen the legs can help young women on the field.