"In the senior years, if you do exercise regularly, such as participating in community-based programs, you can improve your aerobic capacity," said Dr. Nieca Goldberg, chief of women's cardiac care at Lenox Hill Hospital in New York City. "In some studies, the improvement was as much as 15 to 25 percent."

Capacity Declines Steadily

In the latest study, researchers tracked more than 800 men and women and found that aerobic capacity declined steadily with age, with the rate of decline increasing as the participants got older. Aerobic capacity declined 3 percent to 6 percent per decade in the 20s and 30s, but more than 20 percent per decade after age 70, according to the report in the July 26 issue of Circulation.

"This translates into frailty and difficulty with independent living," explained lead researcher Dr. Jerome L. Fleg, a cardiologist at the National Heart, Lung, and Blood Institute. "For example, if you have to use 75 percent or more of your aerobic capacity just to make the bed or climb the stairs, you will be quite fatigued trying to do these activities on a regular basis."

The decline is aerobic capacity was greater for men than for women, regardless of their reported physical activity, the report said. Men lost an average of 8.3 percent of their aerobic capacity in their 40s, and 23.2 percent per decade in their 70s.

The situation probably is worse in the real world, since the study included only participants who had not suffered a heart attack or stroke and were healthy enough to do the treadmill testing that measured their capacity, Fleg added.

"Many older people will have disease-related deficits in addition to those brought on by age," he said.

But this decline is not an inevitability, Fleg stressed.

Exercise Improves Capacity

Regular exercise could bring about a 15 percent to 25 percent improvement in aerobic capacity that "would be equivalent to being 10 to 20 years younger," he pointed out. "Over time, your aerobic capacity will decline, but at any given age someone who exercises will have a higher capacity than someone who is a couch potato."

Exercise also helps by countering age-related loss of muscle strength, he said.

According to Fleg, work is needed at the community level to help bring the benefits of exercise to older people.

"We know that supervised exercise training can bring major improvements, but we need to determine what kind of community programs can get older people up and moving," he said.

More information: The benefits of exercise for older people are outlined by the American Heart Association.