Activity Levels Decline Among Schoolchildren

July 16, 2008— -- Computer games, television, a lack of school recess and cuts to physical education classes may all help explain why children aren't getting as much physical activity as they used to.

But now a new study offers insight into exactly how sedentary American youth has become. And the numbers do not paint a pretty picture, particularly as boys and girls enter the post-puberty years.

In the study, published in the July 16 issue of the Journal of the American Medical Association, researchers measured activity levels in 1,032 kids between the ages of 9 through 15 and compared the levels with health experts' recommendations that children engage in at least 60 minutes of moderate to vigorous activity every day.

What they found was that 9-year-old girls and boys did a great job at meeting -- and exceeding -- these exercise guidelines. They got about three hours of moderate to vigorous physical activity a day on both weekdays and weekends.

But as youngsters entered their tweens and early teens, they became increasingly less active.

"About the time of puberty, activity levels start to decline, especially in girls," said Dr. Philip Nader, a lead author of the study and a professor emeritus in the department of pediatrics at the University of California at San Diego. He wrote "You Can Lose Your Baby Fat."

Nader and his colleagues found that young women dropped below the recommended 60 minutes of exercise a day threshold around age 13, while in boys the drop occurred later at 14.7 years old. By age 15, teens exercised for 49 minutes on weekdays and for 35 minutes on Saturday or Sunday.

Although teenagers have more free time on weekends, they don't appear to spend it in physical activity. But what was most surprising to Nader was the sharp rate of decline in movement among the youngsters.

"It was quite significant," he says. "This [bodes] poorly for the direction of society and for our lifelong health.

"Activity is a major determinant of energy balance, and any decline in caloric expenditure doesn't help when it comes to childhood obesity."