The new study, published in the American Journal of Sports Medicine, looked at more than a dozen other studies and found that female athletes who started so-called neuromuscular training routines by about age 14 were 72 percent less likely to hurt their knee ligaments than those who did not get the training until they were college-age.

Among younger athletes, "their neuromotor development is just getting started, so there's more room for improvement," which could explain why the prevention exercises are more effective in this group, said Dr. Cynthia LaBella, a professor at Northwestern University Feinberg School of Medicine, who was not involved in the current research.

The exercises are designed to prevent one of the most frequent major injuries in sports - tears of the anterior cruciate ligament, or ACL, which are often associated with the kind of short stops and pivoting movements common in basketball and soccer.

In the U.S. each year, about 100,000 people have an ACL injury surgically repaired.

Past research has found that after puberty, girls are far more vulnerable to ACL injuries than boys - most likely because of mechanical differences in their body structures and the way they move.

Estimates of ACL injuries among female athletes range from about one tear for every 10,000 games or practices among high school basketball players to about three tears for every 10,000 games or practices among college soccer players.

Although the neuromuscular training exercises can vary, most of them include strength exercises for core and leg muscles, balance training and improving jumping skills.

One program created by LaBella, for instance, involved a 15-minute warm-up routine for soccer and basketball players before practices and games.

Enough research backs up the effectiveness of neuromuscular training that the U.S. Department of Health and Human Services recommends it for kids and teens aged 6 to 17 in its "Physical Activity Guidelines for Americans."

But there has been little research looking at when the ideal time is to introduce the training for young athletes.

So, Gregory Myer, the lead author of the study and a researcher at Cincinnati Children's Hospital in Ohio, pooled data from 14 clinical trials of neuromuscular training and ACL injuries in thousands of girls and young women.

Myer and his colleagues found that when the female athletes who got the training were compared to their peers who didn't, the training apparently offered strong protection - but the effect was more pronounced the younger the girls were when training was introduced.

Overall, athletes who participated in an injury-prevention program were 46 percent less likely to tear their ACL than athletes who exercised as normal.

The younger girls - aged 14 to 18 - who did the training had a little over one quarter (28 percent) the risk of an ACL injury as their peers who didn't have the training.

In comparison, young women who had the training at ages 19 and 20 had half the risk of peers without training. And women who got training after age 20 had the same risk as those who didn't.

Myer said the results support the idea of working on preventing knee injuries at ages younger than are usually targeted.

"Injury rates seem to peak at around 16 years old, and our conclusion we draw from that is we may be missing the mark if we wait until injury rates are peaking and females are probably playing a number of years at high risk," Myer told Reuters Health.

Myer noted that one possible explanation for the age disparity is that as athletes get older, they become more set in the ways that they move.

"You can imagine an athlete, if they're playing and they're 28 years old, they're probably pretty elite, and they have been successful in moving and playing the way they've played, so making changes in that type of athlete is not that easy," he said.

In addition, it's possible that among college-age or older athletes, players with a high risk for injury have been weeded out of the sport, and perhaps those still playing already tend to land and jump in the correct positions and would be less responsive to prevention training.

LaBella said even though the evidence from Myer's analysis doesn't show a benefit for older athletes, she would not recommend against prevention training for them.

"I think they benefit in other ways, not just injury prevention, but perhaps athletic performance," she told Reuters Health.

SOURCE: bit.ly/TrCMwa American Journal of Sports Medicine, online October 9, 2012.

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