The CrossFit workout has been increasing in popularity in recent years. Now, gyms in cities including Los Angeles, New York City and Chicago are teaching the strength training fitness technique to kids as young as 5.
CrossFit is a fitness regimen that focuses on strength and conditioning through aerobic exercise and weight lighting in high-intensity intervals.
Owners of the gyms that offer the kid-centric programs say it's not too dangerous or as intense as the adult workout. They argue high repetition sets of lower weights can help kids boost their cardio, and learn to use their bodies more efficiently.
"We're not loading the kids with weight, we're not pushing them to go past their limits," Shirley Brown of CrossFit LA told CBS Los Angeles. "We want them to have fun, be engaged, and move their bodies."
Doctors aren't so sure kids should be lifting weights, even if they're only 5 pounds.
The American Academy of Pediatrics says strength training should not start for children until their balance and postural control skills mature enough to adult levels, which typically occurs by 7 or 8 years of age. The AAP always say kids should begin with low resistance exercises until they perfect the lifting techniques.
Dr. Tracey Zaslow, sports medicine specialist at Children's Hospital Los Angeles, says as kids grow, their bones, muscles and tendons are maturing. Specifically, their growth plates are expanding at the bone.
"It's the most vulnerable area to injury," she told CBS Los Angeles. "That's the concern of doing activities like CrossFit, is that they will push themselves more in a free setting."
She also said kids should be focusing on endurance instead of wanting to get a "six pack" through lifting weights.
But those running the classes, like one at CrossFit LA, say kids are being kept safe and learning valuable skills.
"We have not had a single report of a significant injury suffered by a child. That's hundreds of programs worldwide," CrossFit developers said to CBS Los Angeles.