10-year-old teaches kids to be fit (and he even has a six-pack)

He's a fitness guru with well-defined biceps and enviable washboard abs, who prefers eating fruits and vegetables over junk food. He's also only 10 years old.

CJ Senter may be the most ripped child we've seen since 11-year-old actor Jaden Smith showed off his muscles while promoting last year's Karate Kid remake.The pint-sized, hard-bodied fitness advocate is the star of The Workout Kid, a fitness video series aimed at motivating children to get physically active. His website, www.workoutkid.com, outlines the widespread concerns over childhood obesity.

But CJ's appearance on ABC's Nightline this week has also raised questions about whether he's setting a healthy example, and where to draw the line between getting kids off the couch and encouraging them to become fixated on attaining lean, toned bodies.

One youngster tells Nightline he exercises to one of CJ's workout videos every day, and claims to have lost 10 pounds within weeks. Whether true or not, it's a little unnerving to hear a child speak so seriously about shedding weight.

As the Huffington Post notes, health experts also warn about injuries among children.

"In my practice now, I've seen a doubling of injuries to young kids age 10 or nine or eight, with overuse injuries because they're doing more now," says Dr. Robert Gotlin, director of Orthopedic and Sports Program at New York's Beth Israel Center.

CJ's parents tell Nightline they don't push their son to be fit, and that he developed his physique through exercise and "normal play for a child," not weightlifting.

Meanwhile, U.S. first lady Michelle Obama, crusader against childhood obesity, is aiming to set a world record today or the most people doing jumping jacks within 24 hours. She has led some 400 students in one minute of continuous jumping jacks in Washington, D.C., the Associated Press reports, while more than 20,425 people from around the world must join in by 3 p.m. EDT to set the record.

What's the best way to address childhood obesity without encouraging children to become too fixated on fitness?