Most U.S. teens age 15 not active enough

SAN DIEGO, July 16 (UPI) -- U.S. teens become more sedentary as they get older, with fewer than one-third meeting recommended physical activity guidelines at age 15, researchers say.

Dr. Philip R. Nader of the University of California-San Diego in La Jolla and colleagues collected physical activity data on 1,032 children from age 9 to age 15. The children wore an accelerometer, a monitor worn on a belt that records movement, for a week when they were age 9, 11, 12 and 15.

The researchers found that the range of minutes spent in moderate to vigorous physical activity, or MVPA decreased as children moved into adolescence. At 9 years, children engaged in MVPA about three hours per day on both weekdays and weekends. By 15 years, adolescents were engaged in MVPA for 49 minutes per weekday and 35 minutes per weekend day.

The study, published in the Journal of the American Medical Association, finds that age 9 and 11 years, almost all children met the guidelines of of 60 minutes of MVPA per day, but by 15 years, 31 percent and 17 percent met guidelines on weekdays and weekends, respectively.