While children vary in how active they are, they are consistent in the amount of physical activity they engage in every day, regardless of the amount of school-based physical education they receive, their daily routine, background or culture.

According to British investigators, these findings imply that children's physical activity is not determined by the environment but by some internal regulator of sorts that all children share, according to their paper in the International Journal of Obesity.

"There has been a lot of concern regarding the serious loss over the past decade for children to have opportunities for physical activity at school," Dr. Terry J. Wilkin stated. "We believed that the loss of physical education would have its greatest impact on children attending school in areas of low socioeconomic status."

Wilkin and his colleagues at the Peninsula Medical School in Plymouth studied the physical activity of children ages 5 to 10 in a variety of schools.

The team compared several different situations: Group 1, which included 307 children from 53 primary schools who were tested at ages 5 and 6. Group 2 included 215 children ranging in age from 7 to 11 years, selected from three schools representing high income areas and areas of lower socioeconomic status. Group 3 included 732 children attending school in Glasgow, approximately 800 km away.

The three schools in Group 2 included a private preparatory school with 9 hours per week of physical education; a village school with 2.2 hours per week of physical education, and an inner city school that had physical education only 1.8 hours per week.

Each subject wore a matchbox-size accelerometer for 7 days. The device records the time along with duration and intensity of activity, which is then downloaded into a computer at the end of the week.

"Predictably, children who went to private school had a lot more physical activity during the day compared with the schools in lower socioeconomic areas," Wilkin said. "But when we looked at the activity after school, it was entirely reversed. Then when we added in-school and out-of-school activity altogether, it was exactly the same."

"At the end of the week, the difference was less than 0.1 percent between groups," he added, because each child compensates by increasing activity after school.

The researchers also found that total levels of physical activity were the same on week days and weekend days. Similar findings were obtained when comparing children who walked to school with those transported by car, or when they looked at children in the Glasgow school system versus those in Plymouth.

Moreover, total physical activity scores were independent of the amount of time spent sleeping or watching TV or playing video games, the investigations note.

"There was about a 4-fold variation in activity in each group," Wilkin noted, "that is, some children do four times more activity in a day than others. But the point is, the degree of variation was the same at each school, and the average for each school was the same." The researchers also found that girls were consistently less physically active than boys.

"So if environmental differences do not explain this variation, there must be something else," Wilkin continued. "We called this the 'activitystat,' a kind of thermostat in the brain that sets activity levels for each particular child."

SOURCE: International Journal of Obesity, June 2006.