NEW YORK (Reuters Life!) - Regular workouts with free weights or exercise machines can help children and teenagers boost their muscle strength, in some cases by as much as 40 percent, according to a German review of recent studies.
Although strength training was long thought to pose an injury risk for school-age children and adolescents, studies in recent years have shown there is actually no greater risk than with other types of exercise or sports -- and in some cases, less.
In addition, benefits in the form of decreased body fat, increased bone density, and boosting performance and limiting injury risk in other sports, generally outweighed any risks.
In a study reported in the journal Pediatrics, Michael Behringer and colleagues from the German Sport University Cologne combined the results of 42 previously unpublished studies to confirm this training does increase children's strength safely.
Strength training can be done using free weights, exercise machines, elastic bands or the body's own resistance.
"Since resistance training in children and adolescents is known to be safe and to be associated with several health benefits, children and adolescents should be generally encouraged to participate in a resistance-training program," Behringer told Reuters Health.
The studies involved a total of 1,728 children who were randomly assigned to perform supervised strength training or serve as a control group.
In most of the studies, the youngsters used free weights or resistance-training machines, anywhere from one to five times a week, for an average of 42 minutes per session. The duration of the training ranged from one month to just over a year.
The average strength gain varied widely among the studies, but in the majority the kids improved their strength by 20 percent to 40 percent of starting levels.
Exercises involving what are known as isotonic contractions -- bicep curls, squats and bench presses, for example -- appeared to be most effective.
Not surprisingly, a few weekly sessions worked better than one, and longer training duration was more effective than a short one. Gains were greater among kids above the age of 10.
"Our data underlined once again that it (a resistance-training program) is effective over all phases of maturity," Behringer said, adding that professional supervision is a must.
Reporting by Amy Norton at Reuters Health; editing by Elaine Lies