Only Hearty Exercise Keeps Kids Fit and Lean

Adolescents who engage in moderate or vigorous physical activity may increase fitness, but only relatively large amounts of vigorous exercise also is linked to lower body fat, according to a new report.

A group of investigators recruited 421 teenagers from high schools around Augusta, Ga., to participate in a study of physical activity. After an exam to determine each person's height, weight, and physical health, each participant was given a device that measures movement over a period of time.

After a week, the devices were analyzed to determine how physically active each participant had been. Overall, researchers found greater cardiovascular fitness, as measured by a treadmill test, among those who engaged in higher levels of moderate and vigorous physical activity. A lower percentage of body fat was associated with vigorous physical activity, but less so with moderate physical activity.

Because the study was uncontrolled, there are limitations. Some participants may be less physically active because they are overweight or have inherited tendencies. Nonetheless, the authors conclude that to stay or become more lean, adolescents should be encouraged to engage in physical activity that is as vigorous as tolerated. Teens who are less fit should perform moderate physical activity and regulate their diet, gradually progressing to more vigorous activities.

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