The right measure

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You’re a parent and you want to do your best to be sure your children remain healthy. So you worry about physical activity. How much exercise is enough? Will being active protect them from diabetes, cancer or heart disease later in life? Will it prevent them from getting fat? You’ll 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.

But the problem in making recommendations is lack of good data. It’s not that experts haven’t tried. For example, a few years ago, the CDC 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, noted that the group reviewed 850 published papers on the subject. 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. Exercise researchers caution that some of the reputed benefits of physical benefit may be oversold. 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.

Still, exercise researchers do have some advice for parents: Let the children decide what physical activity they want to do.