Female athletes are between two and six times more likely to tear their anterior cruciate ligaments (ACLs) than their male counterparts are—a problem that provokes Tim Hewett of the University of Cincinnati School of Medicine. “I grew up in a house with six sisters—and most of them were better athletes than me,” he says. One tore her ACL playing ball, and Hewett now has a $3-million grant from the National Institutes of Health essentially to figure out why.

Hewett’s hunch is that females’ additional risk of injury has something to do with neuromuscular control and how athletes manage their body’s movements through space. In a paper published last year, Hewett and his colleagues reported that training female athletes to use their musculature to better absorb force and properly position their knees, feet and trunks lowered their risk of knee and ACL injuries by 30 to 80 percent. “If females are five times more likely to sustain an injury, an 80 percent decrease in risk is going to bring them down to where the males are,” Hewett says. “What that says to me is that a big player in this difference is neuromuscular control.”

Hewett has been working on the problem for 15 years, first identifying neuromuscular quirks that are significantly more common in young female athletes than in males—especially in females who go on to get injured. His experimental subjects: “every soccer and basketball player in the sixth through 12th grades in the entire [Boone County, Kentucky] school system,” he says. “We bring ’em in by the busload.” Hewett and his co-investigators attach 37 reflective markers to each athlete’s body and then watch them play. By recording the kids’ movements as they run and jump, zigzag and land—all on a floor covered with force plates—Hewett and his colleagues can generate computer models of their every motion and measure the amount of force on their joints.

Reviewing that data, Hewett has learned several things. First, boys flex their legs and use their muscles—their hamstrings, in particular—to keep the floor from pushing their knees around when they land from a jump. Girls tend to use their quadriceps—the large muscle group on the front of the thigh—a practice that actually puts more stress on the ACL. In addition, Hewett found, injuries tend to happen when the athletes put all of their weight on a single leg or foot.

“The good news,” Hewett says, “is that we can address each of these things.” He gives the girls exercises to increase the strength of their hamstrings. He videotapes them or has them train in front of a mirror so they can see what they’re doing—for example, letting their knees collapse inward when they land from a rebound—and learn to avoid it. He also has them practice balancing, hopping and even squatting on one leg at a time to build up strength on both sides. “It’s great exercise,” Hewett says, and the benefits go beyond the basketball court. Most of us have muscular imbalances between our left and right sides, which is a risk factor for hip fracture, he points out. “So any way you can make yourself more symmetrical, your overall health is going to improve.”

For osteoarthritis, Hewett says that preventing injury, especially to the ACL, is the way to go. “Our current treatments lead to as high or higher a rate of osteoarthritis than leaving things alone,” he says. “So right now the only treatment that’s shown to be efficacious is prevention.”