RESEARCH TRIANGLE PARK, N.C. -– The increase in childhood obesity may be due in part to the decline in children's physical activity as they age, according to a new study by researchers at the University of California, San Diego; University of Arkansas; University of North Carolina at Greensboro; and RTI International.

The study, published in the July 15 issue of the Journal of the American Medical Association, found that children's moderate-to-vigorous physical activity decreased by more than one-third as they aged from 9 to 15. Moderate to vigorous physical activity consisted of all types of physical activity, including walking.

"While we all knew children and youth were moving less, the magnitude of the rate of decline calls for renewed action to improve activity levels in the population," said Phillip Nader, M.D. at the University of California, San Diego and the study’s lead author. "Physical activity is a crucial part of the energy equation; declining physical activity will only complicate the obesity epidemic."

The study measured the physical activity of more than 1,000 youths in 10 cities, beginning in 2000, when the children were 9-years-old and ending in 2006, when the youths reached age 15.

The researchers found that at age 9, children engaged in about three hours of moderate-to- vigorous physical activity per day during the week and on weekends. By age 15, children were physically active only 49 minutes per day during the week and 35 minutes per day on weekends, much less than the recommended 60 minutes per day.

The study showed that boys were more active than girls, spending 18 more minutes per weekday and 13 more minutes per weekend day engaged in moderate-to-vigorous physical activity. However, the rate of decline as they aged was the same for boys and girls.

"Program and policy action are needed immediately at the family, community, school, health care, and governmental levels to find ways to encourage children to remain active as they get older," said Renate Houts, Ph.D. a research statistician and psychologist at RTI and co-author of the study. "Unless parents, elected officials, volunteers and philanthropic organizations begin creating new opportunities for children’s activities, childhood obesity rates will likely continue to rise."

During the study, the children's physical activity was measured using an accelerometer that recorded minute-by-minute movement counts. Participants wore the monitor on a belt around the waist during waking hours for five weekdays and two weekend days, excluding showering, bathing, water sports or contact sports.

This study was directed by the Steering Committee of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Study of Early Child Care and Youth Development and supported by NICHD through a cooperative agreement (U10), which calls for scientific collaboration between the grantees and NICHD staff members. 

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Update on Jul 17, 2008 by At Basil & Spice

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