Kids seem to have an activity "set-point"

Children play on a carousel at a kindergarten in Baokang, Hubei province February 29, 2008.

NEW YORK (Reuters Health) - Increasing the amount physical activity kids engage in at school doesn't mean they'll be more active out of school. In fact, just the opposite may be true, according to study findings presented Thursday at the European Congress on Obesity in Amsterdam.

The results suggest that children who participate in several hours of physical education each week at school compensate by being less active at home. Conversely, the children with the fewest hours of physical education are more active at home.

"We hypothesized that a lot of physical education at school would inculcate a habit," Dr. Terence Wilkin told Reuters Health. "We found it made no difference. What some children lack in school, they make up for -- with remarkable precision -- out of school."

Wilkin, at Peninsula Medical School in Plymouth, UK, believes that children have some sort of "activitystat" that monitors and changes their activity based on their personal set-point.

It is this set-point, and not the environment, that determines whether a child is super-active or a couch potato. Moreover, this set-point, he added, is "strongly defended," which may explain why it is often difficult to change a child's activity level.

The current study involved 206 children, 7 to 11 years of age, from three primary schools with different average amounts of physical education per week: 9.2, 2.4, or 1.7 hours.

The researchers used accelerometers to record the kids' duration and intensity of activity. The devices were worn all day for 7 days during four consecutive school terms.

Children who had the most physical education time per week were 40 percent more active during school than were children in the other groups. However, the total weekly amount of activity was similar in each group.

"These findings have implications for anti-obesity policies because they challenge the assumption that creating more opportunity for children to be active -- by providing more playgrounds, sports facilities, and more physical education time in schools -- will mean more physical activity," co-researcher Alissa Fremeaux, also from Peninsula Medical School, said in a statement.