National Institutes of Health
In a long-term study of more than 1,000 children, researchers at NIH found that at age 9, children averaged roughly three hours of moderate to vigorous physical activity (MVPA) on weekdays and weekends. By age 15, however, they averaged only 49 minutes per weekday, and 35 minutes per weekend - both below the recommended minimum level of 60 minutes per day for a youth that age. The analysis appeared in the July 16 issue of the Journal of the American Medical Association (JAMA).
As examples of moderate physical activity, the U.S. Centers for Disease Control list walking briskly, dancing, swimming or bicycling on level terrain. Vigorous physical activity includes such activities as jogging, high-impact aerobic dancing, swimming continuous laps, or bicycling uphill. Free online. 301-496-5133, http://www.nih.gov/news/health/jul2008/nichd-15.htm. JAMA abstract at: http://jama.ama-assn.org/cgi/content/abstract/300/3/295.