Three decades ago fitness was not a concept that entered the mind of the average child. How things have changed. Turn on any kids' TV channel and you are just as likely to see a mini-aerobics routine designed for them to follow as you are a cartoon for their entertainment. Children's gyms are one of the fastest-growing sectors of the world fitness market. Surveys by the global trade body, the International Health, Racquets and Sportsclub Association, found the under-15s represent the second-fastest growing health club demographic after the over-55s, and gym membership for the six to 11 age group has soared over the last seven years.
Now the target for membership is getting younger still, with classes for the under-fives and toddlers on the rise. To many, the news that a generation prone to obesity is moving about more will be viewed as encouraging. But a growing number of experts are concerned that gyms are not the best places for children to learn how to adopt an active lifestyle. Louise Sutton, the head of the Carnegie Centre for sports performance and well-being at Leeds Metropolitan University, says that well-managed and designed children's gyms "that are not just an adjunct to an adult centre and have specially trained staff who are knowledgeable about child physiology and psychology, might have a place in 21st-century living".
But, she stresses: "The main requirements for activity levels in children should be met by sport and recreational play. They do not actually need gyms at all." In fact, experts at the American Academy of Paediatrics (AAP) committee on sports medicine and fitness have warned that too many gym sessions at a young age can cause mental and physical damage to growing bodies. According to the AAP, fitness classes for the under-eights are not only ineffective in warding off obesity, but can harm under-developed children who are not capable of the sustained activity levels practised by adults. Even for older children and teenagers, too much exercise performed under inadequate supervision can be as damaging as too little.
Particularly risky are any workout programmes that place stress on the joints, such as weight training, aerobics or excessive running on hard surfaces, as they can trigger conditions that force youngsters to be sidelined from any form of activity for months on end. Sutton says strength-training during the pre-pubertal years is particularly risky. "Children can develop strength by moving their own body weight around through exercises such as leapfrogs and piggy backs with their friends," she says.
"But some gyms encourage children to do far more than that and when they lift extra weight or push against a heavier resistance than their joints and bones can cope with, it can lead to structural harm." Stressing young bodies in a negative way can lead to anatomical imbalance, a mismatch of growth rates and so-called "growth diseases". Professor Craig Williams, of the school of sport and health science at the University of Exeter who has studied the effects of over-exercising in young children, says that one of the side effects that is common is chrondomalcia patellae, caused by an imbalance in muscle strength on either side of the knee cap. Teenage girls are more likely to suffer because of their wider pelvises which pull the knee cap over to one side causing a searing pain around the edges of the patella at the front of the knee. It requires children to wear heavy strapping until muscles are re-educated when gentle activity is resumed.
Another problem among young gym enthusiasts is Osgood-Schlatter's, a condition in which the growth plates at the top of the shin bone (or tibia) become inflamed when tendons attached pull hard on it during high-impact exercise. It can affect any child, but is more common among boys and usually strikes between the ages of 10 and 16, when growth spurts reach a peak. Symptoms include a tender swelling on the knee and pain during activity and treatment can involve setting the knees in plaster for up to six weeks. Often the medical advice is to do no sport for up to a year in order to allow growth plates to recover and muscles and tendons the chance to develop fully.
"There are many overuse or overload injuries that can happen when a young person simply attempts too much for their body," Williams says. "It is not just a result of gym training as they can happen simply if a child is too active, but if a child is lifting weights a lot, it significantly raises the risk of this sort of problem." Beyond the physical dangers, experts cite the sterile, almost self-worshipping environment of gyms as possibly having a negative influence on a child's psyche.
Dearbhla McCullough, a sports psychologist at Roehampton University in London and an expert in body-image issues, says that, ironically, gyms can also contribute to poor self-worth by encouraging children to focus more on how they look than how they feel. Several studies have suggested that teenage gym members do have poorer body image than their peers. It seems that for the overweight in particular, rather than helping them to adopt healthier habits and shed pounds, gyms can often damage their already fragile self-image. Plunged into an arena where their weight and appearance becomes a prime focus, they become vulnerable and lack confidence.
"For some people, gyms are simply a means to an end in terms of workouts, that end usually being to lose weight," McCullough says. "If children are introduced to exercise through gyms, the likelihood is that they are going to have weight-loss as a focus. That can be pretty boring as well as soul-destroying. Will they keep up activity to adulthood if they start out in gyms at a young age? I very much doubt it."
So what is the best way to inspire your child to be more active? Sutton says the natural environment, with plenty of toys and access to parks and open spaces, is the best place for pre-schoolers to learn about what their bodies can do. "Getting them to try the exercise programmes on TV is not a good idea because it means the TV-watching will become a habit," she says. For older children, one should encourage sport and general activity.
"Get your children into the habit of walking or cycling," she says. "What they need to learn is that exercise is part of daily life, something that should become natural and be enjoyed. Then it will be effective."