July 21, 2008

Children’s Physical Activity Drops From Age 9 to 15

Photo of a boy and a girl playing leap frog

Physical activity levels dropped sharply in a large group of American children between the ages of 9 and 15, according to a long-term study. By the age of 15, most failed to reach the daily recommended activity level.

The 2005 Dietary Guidelines for Americans recommends that children and adolescents engage in at least 60 minutes of moderate to vigorous physical activity (MVPA) on most, if not all, days of the week. Examples of moderate physical activity include walking briskly, dancing, swimming or bicycling on level terrain. Examples of vigorous physical activity are jogging, high-impact aerobic dancing, swimming continuous laps or bicycling uphill. A lack of physical activity in childhood raises the risk for obesity and the many health problems it can contribute to later in life, including heart disease and diabetes.

To see whether children are meeting these recommendations, a team led by Dr. Philip Nader at the University of California San Diego used data collected for the Study of Early Child Care and Youth Development, a long-term study of more than 1,000 children from ethnically and economically diverse backgrounds that was funded by NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD).

The study collected information on various aspects of children’s health and development. At age 9, the researchers recorded the activity levels of more than 800 children for 4-7 days. Activity was measured with an accelerometer, a device worn on the belt that records movement. The children’s activity levels were assessed again at ages 11, 12 and 15.

As reported in the July 16, 2008, Journal of the American Medical Association, the children averaged roughly 3 hours of MVPA on weekdays and weekends at age 9. By age 15, however, they averaged only 49 minutes per weekday and 35 minutes per weekend.

At ages 9 and 11, more than 90% of the children met the recommended level of 60 minutes or more of MVPA each day. By age 15, however, only 31% met the recommended level on weekdays, while 17% met the recommended level on weekends. On average, boys were more active than girls, spending 18 more minutes per weekday in MVPA than girls, and 13 more minutes per day in MVPA on weekends.

This research highlights the need for action by families, communities, schools, health care systems and governments to help encourage physical activity as children get older. “Helping American children maintain appropriate activity levels is a major public health goal requiring immediate action,” said NICHD Director Dr. Duane Alexander.

Nader said that local school systems can play a major role by ensuring that children receive recess breaks and daily active physical education. He added that local governments could also help by providing safe biking and walking routes around schools.

“But parents don’t need to wait for big changes,” Nader said. “Whenever possible, parents could encourage family walks with their children. Even walking for as few as 15 minutes a day would provide health benefits. On weekends, family outings could be centered on longer walks or biking.”

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