Girl-power news flash: Since the 1972 passage of Title IX, which required that schools receive federal funding so girls could have an equal opportunity to play sports, the number of young women in sports has grown tenfold, from 300,000 to 3.2 million.

What no one anticipated, however, was the corresponding increase in girls’ knee injuries. And almost all these injuries are to one of the four elastic bands of tissue that hold the knee together — the anterior cruciate ligament, or ACL, which makes the knee joint stable.

“Young female athletes are two to 10 times more likely to suffer an ACL injury than a similarly athletic male,” says Tim Hewett, PhD, an exercise physiologist and foremost expert on knee injury prevention in female athletes. What’s more, these injuries peak younger in girls than in boys, at age 16 versus 19.

It might seem that girls who are just beginning a sport are at greater risk, but it’s the opposite. “If you’re very active and playing at a high level,” Hewitt says, “the more at risk you are.”

Why are girls at greater risk for ACLs?

Researchers are still hard at work on this question. Theories abound, from differences in anatomy — post-puberty, girls have a sharper inward hip-to-knee angle than boys — to female hormones that make ligaments looser at certain times of the monthly cycle.

The theory with the most traction, however, has to do with how girls’ vs. boys’ muscular development changes after the pubescent growth spurt. “Kids start out all the same, like a small car with a small, matched motor,” Hewett says. “During the growth spurt, their bodies both go from being a Chevy-sized chassis to a Cadillac-sized chassis. But boys also get a neuromuscular growth spurt, and they get a bigger engine proportionately — a Porsche engine. Girls still have a Chevy-to-Cadillac engine, but not a Porsche.”

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Without this souped-up muscle control, girls’ bodies depend more on their ligaments for stability, he explains. Girls rely more on their legs and trunks than boys, and they tend to put more force on one leg, causing them to absorb force unevenly. In addition, girls have a greater range of motion in their trunk, something that directs the ground force directly to their hip and knee joints.

All this adds up to a recipe for a painful ACL injury, which occurs most often from an uneven landing or impact in which the knee absorbs more than its share of force from the side. Basketball and soccer are particularly risky because the players constantly change directions during the game, putting more stress on the knees.

Related: Signs That “Sprain” Might Be Something More Serious

Prevention strategies

Hewett and other researchers have made it their business to develop prevention strategies to help girls strengthen the right muscles and reduce their injury risk.

“What we’ve shown is that by reducing muscular imbalances and increasing neuromuscular control, you can reduce the risk in young female athletes down to the male level,” Hewett says. His research has shown that regular strength and balance training sessions do just that.

Injury prevention training sessions are relatively easy to fit into your girl’s schedule: two to three 15-to-20-minute sessions per week. The exercises focus on strengthening the glute (butt) and hamstring muscles, improving balance, and honing control when landing on a single leg (as often happens in sports).

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Typically, the training involves a mix of resistance exercises such as hamstring curls and Romanian deadlifts, balance work on uneven surfaces and jumping/landing work, such as repeated single-leg hops with a focus on maintaining good form.

In working with athletes, Hewett uses a few assessment tests to determine a girl’s specific risks, then prescribes the exercises she’ll benefit most from. Self-guided injury training programs are available and your daughter's coach can help you find one. Your daughter, however, should ask her coach or her school’s athletic trainer for advice before starting such a program.

With some customized exercises for regular strength and balance training, your daughter will be in the best position to reap the mental, physical and psychological benefits of being on a team without being sidelined by an all-too-common injury. And as she races down the field toward another goal, that’s another reason for cheering.


Amy Roberts is a certified personal trainer. She writes about fitness, health and a variety of other topics for many well-known publications.