School, Homework, Pump Iron

By KEVIN HELLIKER

Twelve-year-old Amanda Starr and her 10-year-old sister, Natalie, use medicine-ball exercises to build muscle. "I can do 15 military-style pushups," says Natalie, a San Diego fifth-grader, noting that six months ago she could do only seven.

The Starr sisters are part of a nascent muscle-strengthening craze among the nation's young. Strength training, once limited to high school football teams, has become a standard workout feature for participants in youth soccer, swimming, wrestling, basketball and baseball. And it is fast catching hold among kids who don't play organized sports at all.

The percentage of health clubs and community gyms offering youth fitness and strength-training programs is on the rise. Meanwhile, even as gym class fades as a school requirement, weight training as an elective is growing in popularity. At Walter Payton College Prep in Chicago, the student body recently persuaded administrators to open the school's weight room an hour before classes start each morning. "There are 20, 30, sometimes 40 kids in there lifting weights before school—girls and boys," says Arlene Bertoni-Mancine, Payton's physical education chief.

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Natalie Starr, in pink, and her sister, Amanda, practice strength training at home in San Diego with their mother.

The trend is heartening to public-health officials who once opposed strength training for kids but now recommend it as a way to control weight, improve motor skills, increase bone density, normalize blood sugar, lower cholesterol and build confidence. "In the past, PE teachers always emphasized aerobic programs that left bigger kids feeling like failures," says Stephen Ball, a University of Missouri exercise physiologist. "But the weight room is where those kids will develop a love of physical activity."

A large-scale embrace of youth strength-training faces a Catch 22, though. Even the most passionate advocates warn that children should engage in weight training only under expert supervision. But expertise is most common at gyms, health clubs and community centers, where strength-training equipment has often been off-limits to minors. Meanwhile, as more school districts have minimized or eliminated physical education, many school gyms have become the exclusive province of sports teams. "That's the real challenge—providing supervised opportunities for kids in the weight room," says Boyd Epley, director of coaching performance at the National Strength and Conditioning Association, in Colorado Springs, Colo.

Behind the caution is a history of strength-training injuries among children and adolescents. A federal study of strength training by Americans under 21 found that they incurred as many as 26,000 injuries during a five-year period, typically muscle strains involving the back, according to the American Academy of Pediatrics. Whether the rate for adults is lower isn't clear.

And there are sobering long-term implications for athletes who are still growing. In some cases, damage to growth cartilage—almost invariably the result of lifting excessive amounts of weight—can retard growth. And injuries are common among children and adolescents using strength-training equipment at home, according to a position paper issued in 2009 by the National Strength and Conditioning Association. Attributing such injuries to "unsafe behavior, equipment malfunction and lack of supervision," the paper cited the case of "a 9-year-old boy [who] died when a barbell rolled off a bench press support and fell on his chest."

Sandy Huffaker for The Wall Street Journal

Experts say kids' strength-training and aerobic exercise should be fun.

A 2009 study in the Journal of Strength Conditioning analyzed 4,111 emergency room visits because of weight-training injuries, and found that adults tended to suffer sprains and strains while children's injuries resulted largely from dropping weights on hands and feet—"accidents that are potentially preventable with increased supervision and stricter safety guidelines."

"I'm not a fan of strength training at home unless Mom or Dad has a background in PE and understands pediatric strength-training guidelines," says Avery Faigenbaum, a supporter of youth strength-training, a professor of exercise science at the College of New Jersey and lead author of the NSCA position paper. Strength training, he says, is "a lot more fun . . . in a class or with friends."

Yet even among active kids, injury rates from weight lifting are insignificant compared with injuries in sports such as football and soccer. "The risks of weight lifting are blown out of proportion," says the University of Missouri's Dr. Ball.

Experts say weight lifting is safe, beneficial and health-enhancing if children and adolescents follow some simple suggestions. First, they should warm up with a few moments of aerobic exercise or calisthenics. And before lifting actual weights, they should master proper technique, learning to pick up weights from a rack or the floor using leg and core strength rather than one's back. A bicep curl should be performed with a straight back and relaxed neck, engaging only the arm and shoulder.

They should disregard the question, How much can you bench? Never should children or adolescents try to lift their maximum potential. Instead they should limit the load to what they can lift at least six to 15 times in three sets spaced about a minute apart.

As toned stars like Derek Jeter displace Hulk Hogan types as the face of strength training, kids are more easily sold on so-called low-weight high-rep programs. "When you max out on giant weights, you just look big and gross," says Sean McKay, 15, who takes strength-training classes at Fitness Quest 10, a San Diego gym. "Our trainers there taught us that higher reps give you a better tone."

Federal guidelines call for children to engage in an hour a day of physical activity, twice the recommended amount for adults. Since 2008, the recommendation for children has included a call for strength training, or resistance training. By either name, it works muscle groups to the point of fatigue, ultimately increasing muscle mass and bone density, among other benefits.

Strength training need not involve barbells, dumbbells or machines. The safest weight to lift is one's own body. Pushups build muscle in the arms and chest; situps strengthen muscles of the abdomen. Squats strengthen muscles in the legs and buttocks, while pull-ups build the muscles of the back and shoulders.

Brett Klika, director of youth training at Fitness Quest 10 in San Diego, says his adolescent clients often have difficulty initially lifting their own weight. Not until they can do 50 pushups does he introduce them to dumbbells, barbells and kettle bells. For younger clients, such as the Starr girls, strength training consists of climbing and crawling or tossing medicine balls into a bucket. "Exercise shouldn't be medicine—like go run a mile," Mr. Klika says.

Buff role models, such as Michelle Obama and her famous biceps, are stirring youth interest in toned bodies and opening the door to a previously adult establishment—the private health club. Today, more than 25% of health clubs have youth exercise programs. The number of YMCAs offering youth strength-training programs has risen 5% in five years, to 1,054 of the organization's 2,687 U.S. locations. And USA Weightlifting, the governing body that trains and selects America's Olympic weight lifters, has started youth programs in two cities, Chicago and St. Paul, Minn.