(HealthDay News) -- Low levels of activity -- especially a lack of moderate and vigorous exercise -- play an important role in the development of childhood obesity, says a British study that compared the amount of fat in children to their levels of physical activity.

University of Bristol researchers used special techniques to measure the fat mass and activity-related energy expenditure of 5,500 children.

The results showed consistently that the less active children were, the greater their fat mass. This effect was stronger in boys than in girls. The statistical association between fat mass and low activity levels was greater for moderate and vigorous activity than for total activity, the study found.

They acknowledged that their study had certain limitations, but the researchers said encouraging children to be more active should be a major part of efforts to fight the childhood obesity epidemic.

The study is published in the current issue of the journal PLoS Medicine .

More information

The American Heart Association has more about physical activity and children.

By Robert Preidt
SOURCE: PLoS Medicine , news release, March 19, 2007
Last Updated: February 2008
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