LOS ANGELES (KABC) -- What does it take to make it in sports? Some swear by the "10,000-hour rule" - meaning it literally takes 10,000 hours of practice to become a success!
But others say too much play can actually hurt your chances of success.
With every kick and every pass, soccer player Lily Truong is one step closer to her Olympic dreams.
"I started when I was 6 and then started club when I was about 12," Lily recalled.
Teammate Ashley Thomas is right there with her. Along with weekly practices and games, she also does private training.
"The more you put in to it, the more you'll get out of it," said Ashley.
Broken bones, muscle cramps and fractures haven't stopped these girls. They are serious about their sport, and coach Erin Morse says they have to be.
"If you're not putting in the work, someone else is and they're probably, you know, getting better than what you are," said Morse.
The "10,000-hour rule" of sports isn't a long shot for these girls. But David Epstein, author of "The Sports Gene," says the 10,000-hour rule could damage performance and health.
"We're sort of pushing athletes to, first of all, pick one sport, to specialize in one sport, and then to train in a way that's more appropriate for adults and professionals," said the former Sports Illustrated writer.
Epstein's research showed youth are experiencing adult-style injuries, and these injuries are 36 percent more likely in wealthy kids. Also, playing the same sport for eight months can increase the risk. Experts say "sports sampling" until at least age 12 produces the best athletes.
"If you're learning in too professional a style, being sort of explicitly told what to do in doing just the same thing, you're going to inhibit your ultimate athletic development," said Epstein.
He says another problem he found was that youth baseball players should only be throwing 80 pitches every five days. However, many were actually throwing 80 pitches every two days because they played in multiple leagues and many of the coaches didn't communicate with each other.
Excessive sports practices can lead to adult-style injuries for kids, author says
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