One-third of Teens Out of Shape, Study Shows

NEW YORK (Reuters Health) - One in five Americans -- and as many as one in every three adolescents -- may have poor cardiorespiratory fitness, a new study shows.

Cardiorespiratory fitness is the ability of the heart and lungs to respond to an increased workload, Dr. Mercedes R. Carnethon of Northwestern University in Chicago, the study's lead author, explained in an interview with Reuters Health. The less fit you are, the more your heart will pound and the more winded you will feel when you exert yourself.

While poor cardiorespiratory fitness is known to be a risk factor for heart disease and death from heart-related causes, Carnethon and her team note in the Journal of the American Medical Association, the extent of this problem in the US population is not known.

To investigate, the researchers analyzed results from a subset of participants in the National Health and Nutrition Examination Survey (NHANES), including 3,110 adolescents aged 12 to 19 and 2,205 adults aged 20 to 49. All had undergone treadmill tests to gauge their physical fitness.

Participants were classified as having poor cardiovascular fitness if their treadmill test results fell below the 20th percentile for a smaller reference group of people who had undergone similar testing.

Among the teens, 33.6% had low fitness, while 13.5% of adults did. The figure for adults is likely an underestimate, the researchers note, because adults participating in NHANES who had certain heart disease risk factors did not undergo treadmill testing.

Adults and teens with poor fitness had a two- to four-fold increased risk of being overweight or obese. Less fit individuals also had higher cholesterol and higher blood pressure, and lower levels of good cholesterol.

"What's really striking is that even among adolescence we see evidence of cardiovascular disease risk factors being higher," Carnethon said.

She noted that she and her colleagues were not surprised to see so many teens falling into the poor fitness category. For one thing, she noted, fitness "standards and expectations are a little higher, and appropriately so, for youth." She added: "We know from other reports that adolescents are not very physically active. We've seen based on other research that physical activity has declined over time."

"This was the first study to actually put a number on the problem in the U.S. population," Carnethon concluded. "I think that this really provides an estimate of how many people in our country may be at risk from later complications from cardiovascular disease."

SOURCE: Journal of the American Medical Association, December 21, 2005.