Our knees are meant to bend, so let them. Research suggests that most knee injuries happen when athletes land or turn with their knees too straight.

“If you were to jump up one inch off the floor and land with your knees straight, you would feel the shock going from your feet to your head,” says William Garrett, MD, PhD, an orthopedic surgeon at Duke and chairman of the sports medicine advisory committee for the U.S. Soccer Federation.

“But if you let yourself bend a lot," he says, "you are absorbing all that energy with your muscles rather than your joints.”

The most serious knee injuries happen when a ligament tears or breaks, and the most commonly torn is the anterior cruciate ligament (ACL).

Soccer players, basketball players, and people who have a lower percentage of lean body mass are most susceptible to these injuries, Garrett says. And women are five to ten times more likely than males to suffer a torn ACL.

Why women? “Some of the factors are things we can’t control, primarily hormonal factors such as the increase in estrogen and the lack of testosterone,” says orthopedic surgeon Alison Toth, MD, director of the Duke Women’s Sports Medicine Program and team physician for Duke’s women’s athletic teams. These hormonal differences can result in women having more lax ligaments than men.

Reducing Lower Extremity Injuries

Toth and colleagues from the Duke Sports Medicine Center developed the Lower Extremity Prevention Performance Program to reduce the incidence of ACL and other lower extremity injuries and to improve overall performance.

The workouts include exercises to improve balance, flexibility, strength, coordination, and power. Toth suggests that athletes begin injury-prevention training as early as possible, preferably in the young teenage years.

Duke’s Sports Performance Program also offers workshops and clinics to individual and team athletes at every age and skill level. The program incorporates findings from the sports injury prevention research and testing conducted at Duke’s Michael Krzyzewski Performance Research Laboratory.

Garrett and colleagues from Duke and UNC are currently conducting a study of knee injuries in athletes at the U.S. Naval Academy, U.S. Air Force Academy, and U.S. Military Academy.

“We want to figure out what the exact mechanism of injury is and how you can alter your movement patterns to avoid that,” Garrett says.

So far, in tests with about 1,500 subjects, the researchers find that injury often happens when athletes land awkwardly with their knees too straight.

It’s best to get training to improve your balance and your landings, Garrett says. But, when in doubt -- bend your knees.

How to Take it Easy on Your Knees

• Land soft. Your knees should be slightly bent as your feet hit the ground, then bend deeper as you complete the landing. Also try to keep knees slightly bent during turns and position changes.

• Stay strong. A weakness in any one muscle can increase risk for injury. Programs to help avoid knee injuries generally focus on strengthening surrounding muscles such as the hamstrings, quadriceps, and hips.

• Stop when fatigue sets in. Study results suggest that athletes who are tired tend to run with straighter knees, which more often lead to injuries.