For adults, specialization is natural. That’s what we do with our professions. But kids aren’t meant to do just one activity. Youth is a time to explore and experiment with different things. Take sports, for example. The October issue of TENNIS has a feature called “How to Be a Good Tennis Parent.” As a part of the package, we did a fitness article that touched briefly on the importance of kids playing in other sports besides just tennis. In this Olympic year, this idea has gotten a good amount of press, so I thought I’d get into it a bit more here.

“I really don’t encourage early focus on one sport, although you find it to be more normal nowadays,” says Heather Williams, PT, DPT, of the Joint Mobility Center at Hospital for Special Surgery in New York.

So what’s the problem with playing just one sport? Muscle and flexibility imbalances, Williams says (not to mention burnout and loss of interest). In tennis, shoulders, cores, and quadriceps bulk up, while other muscles, like hamstrings, can be underworked. “If they are in one sport and the parents are trying to make them really good and keep them in that sport, then supplementing it with strength training is absolutely necessary [to balance out the body],” Williams says.

While imbalances can be a problem for adults as well, children’s bodies are still developing. “The chronic stress, the same type of movement pattern, isn’t ideal for young kids because their cartilage is more vulnerable to injury at the joints, especially at the ankles, elbows, and knees,” Williams says. She says parents should listen for complaints of pain or locking joints from their kids, and watch for swelling and limping. Back injuries are also common in young tennis players. At the Lawn Tennis Association’s National Tennis Centre in Great Britain, 28 of 33 juniors tested in 2007 had spinal abnormalities like herniated disks and fractures, though none of them reported back pain.

Tennis champions show that it’s possible to become a world-class athlete without sacrificing other athletic activities at young ages. Many of them grew up playing more than one sport. Novak Djokovic comes from a family of skiers and his father wanted him to become either a skier or a soccer player. Anna Chakvetadze says she stays fit by playing soccer.

If the pros, who are totally focused on tennis, do it, maybe your child should, too. Whether it’s playing other sports or strength training and conditioning to keep the body balanced, mixing up workouts is essential to children’s health. Sorry mom and dad, tennis alone isn’t enough.