Caroline Forbess, 9, right, lifts weights under the watch of trainer Bob King at the T Bar M Racquet Club in Dallas, Texas.

DALLAS — It's hard to say what came first — Bob King's idea that kids as young as 8 could benefit from working with child-size weights, or his need to keep his own three boys busy while he helped train professional athletes across Dallas.

"We were his guinea pigs," says his oldest, Aaron, remembering how he and his twin brothers would use his father's hand-engineered adaptations to work out beside the pros. "It was fun."

Aaron King, now 24, liked it so much that he now runs the kids' fitness program under his father's supervision at T Bar M Racquet Club in Far North Dallas. Instead of the equipment his father improvised, Aaron guides pre-adolescents on weight equipment that his father had custom-made to accommodate the smaller limbs of younger kids.

As more kids get into competitive sports, parents wonder how they can nurture their children's goals while protecting them from the injuries that can come from putting so much stress on young muscles, bones and joints.

Bob King, whose career has included coaching in the training rooms of the Dallas Cowboys, Mavericks and Burn, believes that weights accompanied by resistance, flexibility and aerobic training can help children reduce the risk of injury.

"Repetitive motions cause injury," he says. "We try to cut down injuries by helping the muscles handle the stress of the sport. It's fighting fire with fire."

Using my son, Josh, 12, as my own guinea pig, I asked him to try it out. And while results would take at least a month's investment in the program, which limits kids to 20-30 minutes three days a week, there's no question he had fun moving from machine to machine, working out.

Afterward, my 18-year-old, Sam, who became a weight-room enthusiast starting at the more usual age of 16, questioned whether Josh was old enough.

So I asked Dr. Shane Miller, pediatric sports medicine specialist at the Sports Medicine Center, which opened this spring at Children's Medical Center at Legacy, what he thought.

"With proper education and supervision, children may safely participate in a strength program as young as 8," he notes, adding that he also believes kids need to use size-appropriate rather than adult equipment, and have adult instruction and direct supervision. "Appropriate strength-training programs do not damage growth plates or stunt growth."

Both Bob King and Dr. Miller stress that kids should perform exercises with the goal of conditioning rather than lifting more weight.

And with a proper program, Dr. Miller says, strength training in children and adolescents has been shown to improve sports performance and increase strength by as much as 40 percent over a period of eight weeks.

Aaron King adds: "What we're teaching is muscle coordination and the proper technique of how to work out. We're also building confidence."

Certainly the kids I interviewed on the weights, including tennis player Christian Duarte, 14, of Dallas (who had started out on the kids' weights at 11 and graduated to the adult ones at 13) seemed to love it.

"Being able to do all the workouts was a big confidence builder," says Christian. "That gives me what I need to withstand what the other guy is throwing at me."

Wonder if Josh will feel the same way? Check back in eight weeks, if his mom can get it together to get him there three days a week!