``When they go to make these turns and pivots, their hips are straighter and their knees are straighter -- more upright, less squatting,' said Dr. William Garrett Jr. of the University of North Carolina, Chapel Hill. He presented his findings Feb. 8 at a meeting of the American Academy of Orthopaedic Surgeons in Anaheim, Calif.With more force on the front of the leg, women rely more than men do on the quadriceps muscles in the front, and less on the hamstrings in the back, to control their movements, Garrett said. And the additional tightening of the muscles in the front may create more strain on the ligaments in the front, he said.
``The quadriceps muscles have enough force to tear ACLs with the knee at least near full extension,' Garrett said.
Ligament tears, while not rare, are not all that common. NCAA data find female soccer and basketball players were three to four times more likely than men to be injured.
But among every 15 soccer players, only one injury would occur in every 385 games and practices for the men, while one would occur for every 161 games and practices for the women. But the injuries can require surgery to repair, and they can in some cases end an athletic career.
In his research, Garrett and his colleagues looked at 11 male and eight female well-trained, recreational-level athletes. The researchers used three-dimensional videos to examine movement and attached electrodes to the muscles to measure contraction.
About halfway through crosscutting, the males' knees were flexed at about 55 degrees, while the females were at a less-squatted 45 degrees, Garrett said.
``We and others have thought that women in games play more upright,' Garrett said. The study adds data to support this, he said.
However, while the study indicates the stance difference accounts at least in part for the different rates of injury in men and women, it does not provide proof.
The project did not follow a large number of athletes and see who got injured. So Garrett said he cannot assure women that training to run in a more bent-kneed position will reduce the risk.
It's too soon to tell how much importance to give stance as a cause of injury to the tendon, said Dr. Letha Griffin, team physician for Georgia State University, Atlanta.
"With every theory, we have problems and holes,' Griffin said. The orthopaedic surgeons' group is trying to convene a consensus conference to give better guidance, she said.
Other factors also could account for the differences in injury rates, such as differences in male and female biomechanics -- even hormones, commented Dr. Edward M. Wojtys of the University of Michigan.
But stance is a promising cause, not only because the data look good but because stance could be corrected through training, Wojtys said. ``We all hope it's not anatomy; it's the hardest to change,' he said. ``We want to put all our emphasis right now on the biomechanical.'
