"These results are interesting because it wasn't a weight-loss study. More than half the kids who participated were at a healthy weight, and that allowed us to observe how exercise or lack of exercise affected body composition in normal-weight and overweight children," Naiman Khan, a postdoctoral researcher in the division of nutritional sciences at the University of Illinois, said in a university news release.
The study included 220 children who were either 8 or 9 years old. The children were assigned to either a nine-month exercise regimen or to a group with no exercise program (the "control" group). The youngsters in the exercise group took part in a physical activity program for 70 minutes a day, five days a week.
After nine months, the participants in the exercise group "had improved cardiovascular fitness, less overall body fat, and carried less fat around their abdomens, a risk factor for diabetes and heart disease. The opposite was true for the control group who maintained their regular after-school routine," said Khan.
"So the weight of healthy-weight children who don't exercise doesn't just remain stable. Normal-weight kids who don't exercise do gain an excess amount of weight for their age, and if they become overweight, the tendency is to store excess fat in their abdomens. They're going in the wrong direction," Khan explained.
The study was published recently in the journal Pediatrics.
Parents should encourage their children to be physically active, even if they have a healthy weight, Khan advised.
"Your child should engage in moderate to vigorous exercise for about an hour a day. Adults should make sure kids have a space to play and play games in, and opportunities to be physically [active] during or after school. If kids are at a healthy weight for their age, we want to make sure they stay that way," Khan added.
The American Heart Association has more about children and physical activity.