Amount of physical activity by children steadily declines as they get older

July 15, 2008

New research documents the decline in physical activity among children, with less than a third meeting recommended physical activity guidelines by the time they are 15 years old, according to a study in the July 16 issue of JAMA.

Physical inactivity is associated with an increase in obesity and associated illness and chronic diseases among youth. Expert opinion and studies suggest that children need a minimum of 60 minutes of moderate-to-vigorous physical activity (MVPA) per day, according to background information in the article. How many youth meet this standard is unclear.

Philip R. Nader, M.D., of the University of California San Diego, La Jolla, and colleagues collected physical activity data on 1,032 children when they were 9 years old until they were age 15. Physical activity was measured by the children wearing an accelerometer, a monitor worn on a belt that records minute-by-minute movement counts. The children would wear this monitor for one week a year at ages 9,11,12 and 15. The study took place in 10 geographic locations from 2000-2006. Participants included boys (517 [50.1 percent]) and girls (515 [49.9 percent]); 76.6 percent white (n = 791); and 24.5 percent (n = 231) lived in low-income families.

The researchers found that both the average minutes of MVPA and the range of minutes spent in MVPA decreased as children moved into adolescence. At 9 years, children engaged in MVPA approximately 3 hours per day on both weekdays and weekends. By 15 years, adolescents were only engaging in MVPA for 49 minutes per weekday and 35 minutes per weekend day. At 9 and 11 years, almost all children met the guidelines (of 60 minutes of MVPA per day), but by 15 years, only 31 percent and 17 percent met guidelines on weekdays and weekends, respectively. Both weekday and weekend MVPA showed significant decreases in MVPA between 9 and 15 years, with decreases of 38 and 41 minutes per year, respectively.

The estimated age at which girls crossed below the recommended 60 minutes of MVPA per day was approximately 13.1 years for weekday activity compared with boys at 14.7 years, and for weekend activity, girls crossed below the recommended 60 minutes of MVPA at 12.6 years compared with boys at 13.4 years.

"More research is ... needed to understand the reasons for such substantial decreases in youth activity. Further study and more precise descriptions of the immediate activity environment, such as whether youth are located in urban, suburban, or rural areas; availability of safe places to be active; and quality of school-based physical education may explain some of the individual and regional differences noted in this and other studies."

"This decrease augurs poorly for levels of physical activity in U.S. adults and potentially for health over the course of a lifetime. Consequently, there is a need for program and policy action as early as possible at the family, community, school, health care, and governmental levels to address the problem of decreasing physical activity with increasing age," the authors conclude.
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(JAMA. 2008;300[3]:295-305. Available pre-embargo to the media at www.jamamedia.org)

Editor's Note: Please see the article for additional information, including other authors, author contributions and affiliations, financial disclosures, funding and support, etc.

The JAMA Network Journals

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