The numbers bear it out. Since the advent of Title IX, according to the National Federation of State High School Associations, the number of girls playing high school sports has grown more than tenfold, from 294,000 in 1971 to nearly 3.2 million last year.

But this welcome transformation has come at a serious cost for many female athletes. Title IX has inflicted significant collateral damage, including increased health risks for the players, a drop in the number of women coaches, and increased exposure to sexual abuse.

Like their male counterparts, girls have started to specialize early in their careers, working on just one sport year-round, often as a way to capture the attention of college coaches. With more scholarship money available than ever, girls feel pressured to specialize at a young age in the hopes of winning a spot on an elite team or gaining an edge in the increasingly competitive college admissions game. Despite persistent warnings from orthopedic surgeons and trainers, young athletes bent on specialization continue to suffer from preventable overuse injuries, like stress fractures and stress reactions, according to the American College of Sports Medicine. "More than 50 percent of what we see in sports medicine are overuse injuries, which are entirely preventable," said Dr. Joel Brenner, chairman of the American Academy of Pediatrics and the Council on Sports Medicine and Fitness.

Of special concern for girls is damage to their anterior cruciate ligament, or A.C.L., the tiny ligament in the knee that connects the two halves of the leg. Female athletes are four or five times more likely than male athletes to have A.C.L tears, says Dr. William Levine, the director of sports medicine at Columbia University and the head physician for its varsity teams.

As Dr. Levine explains, once girls begin to menstruate, they become more "quadricep-dependent" than males, and that thick slug of muscle in the middle of the thigh then works against the A.C.L., sometimes causing tears. "Female athletes jump and land in a more erect posture, which puts increased stress on their A.C.L," he says.

Girls who participate in endurance sports like distance running, which emphasize leanness, also contend with a debilitating syndrome called the "female athlete triad." By eating too little or exercising too much, or some combination of the two, they start to develop three-interrelated problems: eating disorders, bone loss, and the cessation of their menstrual cycles. While 1.2 to 4.3 percent of all women athletes have the full "terrible triad," as Dr. Levine calls it, 70 percent are thought to have one component of it. Six top sports associations, including the American Academy of Family Physicians and the American College of Sports Medicine, assert that "fifteen to 62 percent of college female athletes report a history of disordered eating"—ranging from bulimia to restricted calorie intake to fad diets—which is higher than the presumably more sedentary general population.