More than one in three American adolescents are physically unfit and have many of the risk factors for heart disease, researchers said on Tuesday.
Treadmill tests performed on 3,100 adolescents revealed 34 percent were in bad physical shape — and the figure was conservative because some couldn't participate due to the risk they might suffer a heart attack during the exam.
In a sign of how the problem is getting worse, one in eight adults aged 20 to 49 who performed the treadmill test were also physically unfit, Northwestern University researchers said.
The 5,315 test subjects were asked to achieve 75 percent to 90 percent of their age-predicted maximum heart rate.
Those who did poorly on the treadmill also tended to have high levels of so-called bad cholesterol in their blood, low levels of good cholesterol, high blood pressure and large waists — although some out-of-shape subjects were thin.
More females unfit than males
In general, the study found blacks and Mexican-Americans were more likely to be unfit than whites. Among adults, more women (16 percent) were unfit than men (12 percent), while the proportion was about equal between teenage girls and boys.
Projecting the results to the entire U.S. population means 7.5 million adolescents and 8.5 million adults are in bad physical shape and at risk for cardiovascular disease and other illnesses such as diabetes, the report said.
"The consequences of declines in physical activity over time are now evident by the large proportion of society with poor fitness levels," said Mercedes Carnethon, lead author of the study that appeared in this week's issue of the Journal of the American Medical Association.
"The correlations between poor fitness and cardiovascular disease risk factors suggest a potential trend of increasing illness and death from chronic diseases — the first sign of which is the burgeoning obesity epidemic," she added.