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YOU’RE a parent and you want to do your best to be sure your children are healthy. So you worry about physical activity. How much exercise is enough? Will being active protect them against diabetes, cancer or heart disease later in life? Will it prevent them from getting fat?
You search for information, for official guidelines on physical activity. And, you soon discover, there is plenty of advice — at least 27 sets of official guidelines, notes Harold W. Kohl, an epidemiologist at the University of Texas School of Public Health in Austin who formerly worked at the Centers for Disease Control and Prevention.
But the problem in making recommendations is a lack of good data.
We can’t “clarify the dose of physical activity and exercise that’s good for kids” as precisely as we think we can, Dr. Kohl said.
It’s not that experts haven’t tried.
For example, a few years ago the C.D.C. convened a panel of experts to review published papers and make the best recommendations. The panel’s co-chairman, Robert M. Malina, a professor emeritus of kinesiology and health education at the University of Texas at Austin, noted that the group reviewed 850 published papers on the benefits of regular exercise for school-age children and adolescents.
In 2004, the panel concluded by recommending that children and adolescents get 60 minutes of moderate to vigorous physical activity every day. Why 60 minutes and not 30 or 45? It was, Dr. Malina said, “a gut reaction” to the body of evidence.
Now, the Department of Health and Human Services is preparing a new set of guidelines, but most of the same questions remain, Dr. Kohl said. And even though he, Dr. Malina and most other exercise researchers enthusiastically endorse physical activity for everyone, they caution that some of its reputed benefits may be oversold.
In reviewing published papers, the C.D.C. and Human Services panels asked: How good are the data? They learned that, with a few exceptions, for every purported benefit, the evidence was often marginal or equivocal. And, Dr. Malina said, even in situations in which exercise has demonstrable effects, there are marked differences among individuals: some children will get more benefit than others and some will not get any at all.
The undisputed benefits of exercise, the panels said, are that it can lead to stronger muscles, greater endurance, and bones that are denser and have greater mineral content. In addition, when obese children exercise regularly, their body fat, blood lipids and blood pressure may fall. Exercise, though, has not been found to have those effects on healthy children of normal weight.
Even there, though, uncertainties remain, Dr. Kohl said. “Kids aren’t little adults, and they don’t do things for 30 minutes straight through,” he said. “You can put kids on treadmills and train them and that can somewhat help obese kids reduce their adiposity levels, but when you get out in the real world it’s not that easy.”
The panels asked whether exercise alleviates symptoms of anxiety or depression or whether it improves self-image. The studies were not large enough to draw conclusions, they said.
Another issue is academics. Do physically active and physically fit children do better in school? Do they have qualities, like an improved ability to pay attention, that might predict better academic performance?
The answer, Dr. Kohl said, is not known. “The only good data we have indicate that participation in a better physical education program does not negatively affect test scores,” he adds.
Parents sometimes are advised to get children involved in activities that they can do throughout a lifetime — walking, cycling or swimming. But, Dr. Malina said, there is no good evidence that the sport someone does as a child will affect activity as an adult.
“The evidence that tracks youngsters to adulthood is very relatively meager,” Dr. Malina said. And, he added, it is not clear how and why people change activities during their lives.
“I played all sorts of sports growing up,” he said. By the time he started college, he adds, “baseball was my sport.” Now, said Dr. Malina, who is 71, “in my old age, my activity is walking.”
Still, exercise researchers do have some advice for parents: Let the children decide what physical activity they want to do.
“The single best activity you can do is the one you will do,” said Charles B. Corbin, a professor emeritus in the department of exercise and wellness at Arizona State University and the author of more than 80 books on fitness.
And the mistake parents often make, Dr. Malina said, is to decide in advance which sports their children should pursue.
“All too often, youngsters do not have a choice in the decision-making process,” he explained. And, he said, no matter how much parents may want their children to be physically active, “if it is not fun, the child will not do it.”
Sources: The New York Times
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