CHAPEL HILL, N.C. — The anterior cruciate ligament (ACL) is only three centimeters long, but tearing the ligament in the knee can end or put an athlete's career on hold. A researcher at the University of North Carolina at Chapel Hill claims he has a theory as to why women are far more likely to injure their ACL than men.

Although ACL injuries can happen when one player collides with another, the injury itself is usually motion-related. It is also an injury that is two to eight times more common in women than men.

To figure out why, Dr. Bill Garrett, an orthopedic surgeon at the University of North Carolina, studied male and female athletes. Using 3-D cameras, he recorded each players' movements. He found that women tend to land with straighter knees than men, which puts more force on the knee, putting her at risk for an ACL injury.

Garrett said the difference is not physical, but a learned behavior. He feels the discovery will lead to ways to better train female athletes to protect themselves.

"If you can learn a new way of thinking that's safer, maybe we'll be less likely to injure ourselves," he said.

Amy Steadman feels at home on the soccer field. The 17-year old left high school early to play soccer at UNC, but her career nearly ended last October when she tore her ACL. She knows how hard it is to get back on your game after an ACL injury.

"Technically, I think I'm back and confidence-wise, I'm back. All the things like speed and agility, they aren't back," Steadman said.

Garrett said the learned behavior starts early, usually around adolescence. Before around age 13, ACL injuries among athletes are rare.