It’s no secret that kids today aren’t getting as much exercise as they once did. “Children are spending so much time in classrooms, PE budgets have been cut, and some elementary schools no longer have recess,” says Wayne L. Westcott, PhD, professor of exercise science at Quincy College in Massachusetts and co-author of several research studies and books on youth strength training. “

Unless a child is playing sports, she’s not getting the appropriate amount of stress on her muscles and bones for optimal strength and development, he says. It’s for this reason and others that the American Academy of Pediatrics (AAP) recommends strength training sessions two to three times per week for kids age 8 and above.

The benefits of strength training

Because kids sit so much today, in the year a girl is nine years old, her bone density will increase by only about 1.9 percent. If that same girl does regular strength training, her bone density increases by about 6.2 percent.

“The activities kids are doing in regular life aren’t enough,” says Westcott.

Another reason for strength training: weight control. More kids are overweight than ever before. And while it’s easy to say you should just encourage them to be more active, Westcott points out that overweight children struggle with the common endurance-focused activities that kids are inclined to do. “The overweight kid doesn’t like to play tag, because he’s always ‘it,’” he says. “He’s not as good at coordination and balance, either. But what he can do equally well is lift weights, and he will likely be able to do more reps than his slimmer peers.”

Not only does strength training instill confidence, it also has a proven afterburn effect. A child’s resting metabolic rate — the rate at which he burns calories — is elevated for two to three days after a training session. “After a session, a child may burn 100 calories more per day just by being,” Westcott says. “With two sessions per week, that translates into a 3,000 calorie deficit, or a pound of body fat, in a month — not including the calories burned during the session itself.”

Kids who are already athletically inclined can benefit, too, by gaining ability and confidence and also by reducing their risk of injuries in their chosen sport. “They build muscle, improve their conditioning, and get more excited about sports, becoming even more active,” says Westcott. They may also take more enjoyment in recreational activities such as hiking and kayaking, because they’re stronger and don’t fatigue as easily.

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Safety guidelines for kids

In his research, Westcott and his colleagues have tried many strength-training regimens with children. What they found works best couldn’t be easier to implement: A sequence of 8 to 10 basic exercises that work each of the major muscle groups using dumbbells, resistance bands or simple body weight. They learned that some kids, particularly ones who are overweight, do better with the external resistance of weights and bands than with trying to move their own body weight, especially with upper-body exercises.

Each exercise is done for 8 to 12 reps, then kids rest a minute before going on to the next move, and the whole sequence is done just once through. “Kids often ask to do more, but we don’t want them to fatigue or end up sore, so they may not want to come back and do it the next time,” he says.

Once a child finds 12 reps too easy, the amount of weight is increased slightly to up the challenge. Two to three sessions per week are ideal for the child who isn’t otherwise involved in sports.

Westcott ended the strength-training sessions he conducted in his programs at a local YMCA with 15 minutes of general activity, or what he calls “fun and games.” “You want to keep it brief and basic and safe and sensible,” he says. He also points out that before puberty, girls and boys are equally strong, so coed sessions are no problem.

If you don’t have a kids’ strength-training class available locally, consider the iPhone app IronKids ($3.99, iTunes.com), created by the AAP and Jordan Metzl, MD, a sports medicine pediatrician. It includes a 45-minute workout using dumbbells and body weight, as well as info on how to help kids set fitness goals, create a workout schedule, choose exercises and more.

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Amy Roberts is a certified personal trainer. She writes about fitness, health and a variety of other topics for many well-known publications.