One out of three U.S. adolescents is physically unfit, putting them at increased risk of heart disease when they get older

Liz Szabo:

In a study in Wednesday's Journal of the American Medical Association, researchers asked kids to walk or run on a treadmill, then measured their heart rate and blood pressure.

About 34% of 3,110 adolescents fell into the bottom fitness level.

Unfit kids tended to have other health problems, too.

They were more than twice as likely to be overweight, according to the study. They were two to three times as likely to have high cholesterol than kids with higher fitness scores.

Black girls and Mexican-American boys were the least likely to be fit, according to the study.

Based on the study's results, researchers estimate 7.5 million adolescents between ages 12 and 19 nationwide are unfit, says Mercedes Carnethon, lead author and assistant professor of preventive medicine at the Feinberg School of Medicine at Northwestern University in Chicago.

Researchers evaluated kids using the FITNESSGRAM program, a commonly used and highly regarded health assessment based on a child's age and sex that was developed by the Dallas-based Cooper Institute.

Participants were drawn from the National Health and Nutrition Examination Survey, organized by the Centers for Disease Control and Prevention.

Nearly 14% of adults 20 to 49 who took the treadmill test also were physically unfit. Those over 50 and people with serious health problems were excluded from the treadmill test for safety reasons, so the true number of out-of-shape adults is probably much higher, Carnethon notes.

For years, health experts have been concerned about kids eating more and exercising less than previous generations. About 31% of U.S. children are overweight or at risk of becoming so, according to the CDC.

The new study may be more precise than older surveys about physical activity, says James Hill, who directs the Center for Human Nutrition at the University of Colorado Health Sciences Center in Denver.

Many earlier surveys relied on children to accurately remember how often they exercised, says Hill, who did not contribute to the paper.

Carnethon says her study is the first to measure fitness objectively in a large population of adolescents and adults.

Richard Milani, a preventive cardiologist at the Ochsner Clinic Foundation in New Orleans, says he is "very concerned" about this generation of children. "These are the future heart patients of tomorrow," he says.

Hill says the study should serve as a "wake-up call," telling parents to improve their children's health.

"It doesn't work to lie there on the couch and tell them to go out and be more active," Hill says. "If kids see their parents as being active, they get the message."

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