The amount of exercise children in the USA get each day drops dramatically from ages 9 to 15, according to one of the largest studies ever done on the activity levels of children.
In fact, fewer than one-third of 15-year-olds get 60 minutes of moderate to vigorous physical activity a day, the minimum amount recommended for children by the federal government.
Inactivity has been shown to contribute to obesity. One-third of children in the USA -- about 23 million ages 2 to 19 -- weigh too much, which puts them at an increased risk of type 2 diabetes, high cholesterol and other health problems.
In the latest study, researchers measured and analyzed the activity of more than 1,000 children from 10 different cities from 2000 to 2006. The kids wore monitors called accelerometers for four to seven days during the school year when they were 9, 11, 12 and 15. The accelerometer, which measures movement, tracked activities such as playing tag, biking, jumping rope, dancing, walking briskly and running, and playing non-contact sports.
The data are part of a long-term study by the National Institute of Child Health and Human Development, part of the National Institutes of Health. Among the findings, in today's Journal of the American Medical Association, on how many hours kids spend in moderate to vigorous exercise:
*9-year-olds spent an average of three hours each day.
*15-year-olds spent an average 49 minutes on weekdays and 35 minutes on weekend days.
*Only 31% of 15-year-olds exercised at least one hour on weekdays; only 17% did that much on the weekend days.
*Overall, boys were more active than girls, exercising an average of 18 more minutes on weekdays and 13 more minutes on weekend days.
As kids get older, they clearly aren't getting enough exercise either in school, after school or at home, says Philip Nader, lead author of the study and an emeritus professor of pediatrics at the University of California-San Diego.
Nader says barriers to activity, such as a lack of safe places to play and the elimination of P.E. programs in schools, must be removed. "We really have to think outside the box and find more interesting activities for kids this age," he says. "It's got to be fun."
On the weekends, families should go on walks together, bike together or shoot hoops, Nader says: "That would be a step in the right direction."
James Griffin, deputy chief of the Child Development and Behavior Branch at NIH, says some decrease in activity can be expected as children age. They go from a time when they are involved in more spontaneous play to adolescence, when they are more likely to participate in group sports.
Griffin says parents should try to make sure their teenagers stay active, and they should encourage them to do even simple things such as walking the dog or playing basketball.
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