Teens less active than children, study finds

One of the largest studies of its kind shows just how sluggish American children become once they hit the teen years: While 90% of 9-year-olds get a couple of hours of exercise most days, fewer than 3% of 15-year-olds do.

What’s more, the study suggests that fewer than a third of teens that age get even the minimum recommended by the government -- an hour of moderate-to-vigorous exercise, like cycling, brisk walking, swimming or jogging.

The sharp drop raises concerns about inactivity continuing into adulthood, which could endanger kids’ health throughout their lives, the study’s authors said.

“People don’t recognize this as the crisis that it is,” said lead author Dr. Philip R. Nader, a pediatrician and professor emeritus at UC San Diego.

Inactivity is linked with greater risks for many health problems, including heart disease, obesity, high blood pressure and diabetes.

The new findings come soon after an influential pediatricians group recommended that more children have their cholesterol levels checked and that some as young as 8 be given cholesterol-lowering drugs. That advice was partly out of concern over future levels of heart disease and other ailments linked to rising rates of childhood obesity.

The latest study, published in the Journal of the American Medical Assn., tracked about 1,000 U.S. children from 2000 until 2006.

Special gadgets were used to record their activity. Average levels of moderate-to-vigorous activity fell from three hours a day at age 9 to less than an hour at age 15.

Nader said he was “surprised by how dramatic the decline was” and cited schools dropping recess and gym classes and kids’ increasing use of video games and computers as possible reasons.

The National Institute of Child Health and Human Development funded the research, calling it one of the largest, most comprehensive studies of its kind to date.

James Griffin, science officer for the study, said that as children mature, “you would expect somewhat of a decline [in activity], but nothing of this magnitude.”

He noted that the study coincided with the rise in popularity of video games, DVDs and Internet use -- “all of the types of things that take children from outside and put them on a couch or in front of a computer.”

Griffin said the results send a message to parents that it’s important to teach their kids to balance computer time with more active pursuits, like walking the dog or shooting hoops.

Study participants were recruited from 10 hospitals around the country. Family income, race and ethnic background closely matched the U.S. population.

The researchers tracked the children’s activity levels starting at age 9, using an accelerometer -- a device about the size of a small belt buckle that was attached to a belt around the waist and recorded movement. Activity levels were monitored at ages 9, 11, 12 and 15 during the school week and on weekends.

The method wasn’t foolproof because the device wasn’t worn during swimming and contact sports. But the researchers said it’s unlikely that such activity happened often enough among the children studied to skew the results.

Through age 12, well over half the children got at least the government-recommended amount of activity every day. By age 15, less than a third were that active on weekdays, and only about 17% were on weekends.

Boys were more active than girls at every age. But by age 15, even boys’ activity levels fell short of recommendations, particularly on weekends.