10/11/2011 03:35 pm ET Updated Dec 06, 2017

Workout Kids Push The Limits Of Safe Exercise

With childhood obesity more than tripling in the past 30 years, it seems commendable for a child to take on fitness the way 10-year-old CJ Senter does. Professionally known as The Workout Kid, CJ boasts a six-pack and a DVD fitness series designed to help kids get active. He also plays running back on a local football team, runs the 200 meter, the 100 meter and the 50 meter track events, and says he prefers fruits and vegetables over sweets and snacks.

In a Q&A on his website, CJ lists one of his favorite family activities as going outside and playing catch with a football. "Whoever drops it has to do pushups," he says.

But just how safe is it for kids CJ's age to train and diet the way he does? ABC's "Nightline" asked the experts to weigh in.

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"In my practice now, I've seen doubling of injuries to young kids, age 10 or 9 or 8, with overuse injuries because they're doing more now," Dr. Robert Gotlin, director of Orthopedic and Sports Program at Beth Israel Medical Center in New York City, told "Nightline." He recommends children work out up to an hour per day, with water breaks and mixing up their exercise -- such as aerobics, lifting weights.

In addition to physical stress, experts caution that exercising beyond the requirements for good health can signal compulsive behavior, though CJ's parents insist that they have not pushed their son into being super fit. "If anything," "Nightline" reports, "the little fitness guru said he has been pushing them to shape up, encouraging them to exercise outside."