As they get older, U.S. kids exercise less: study

By Will Dunham

WASHINGTON (Reuters) - U.S. children turn away from exercise in droves in their early teen years after getting much more exercise when they are younger, according to a study spotlighting a factor in the rise of youth obesity.

The research, published on Tuesday in the Journal of the American Medical Association, documented a steady decline in physical activity in 1,032 children in 10 places around the United States who were followed from ages 9 to 15.

Less than a third got the recommended levels of physical activity at age 15, the study found.

The findings do not bode well for the health of this generation in the decades ahead, the researchers said.

"We're dealing with an obesity epidemic," pediatrician Dr. Philip Nader of the University of California at San Diego, who led the study, said in a telephone interview. "I don't know what it will take for society to wake up and say, 'What's happening here and what can I do?'"

The researchers had each child in the study, which ran from 2000 to 2006, wear a small device called an accelerometer, which monitors physical activity, for one week at a time when they were ages 9, 11, 12 and 15.

At ages 9 and 11, more than 90 percent of the children met the recommended level of at least an hour per day of moderate or vigorous exercise. But by age 15, only 31 percent hit the recommended level on weekdays -- and just 17 percent met the mark on weekends, the researchers found.

Boys did better than girls, but both showed the same pattern of declining activity as they got older.

Girls fell below the recommended level of an hour a day on average at age 13 for weekdays and age 12-1/2 for weekends. On average, boys slipped below the recommended amount of exercise at age 14-1/2 for weekdays and age 13-1/2 on weekends.

'LOST OPPORTUNITY'

If a person fails to establish good patterns in physical fitness early on, it is much harder to do so later in life, according to James Griffin of the U.S. National Institute of Child Health and Human Development, part of the National Institutes of Health, which backed the study.

"The concern is not only obesity, but also the lost opportunity to build muscle and bone. Those are both happening right around puberty. If you don't build it then, it's that much harder to do it later," he said in a telephone interview.

Exercise helps a person maintain a healthy weight, delay or prevent the most common form of diabetes and ward off heart problems and some types of cancer, according to experts.

Previous research has shown a drop in exercise by American children in recent decades. U.S. youth obesity rates have tripled since 1980, although they leveled off this decade.

The government says 32 percent of U.S. children are overweight and 16 percent are obese.