The findings might be useful to help motivate elderly people, who often fear that exercise is bad for them, another expert said.

A team led by Lance Davidson of Queen's University in Kingston, Ontario, and Columbia University in New York, studied 136 sedentary older adults with abdominal obesity, a build-up of fat around the waist that raises the risk of heart disease and other problems.

They were placed in one of four groups: A group that did resistance exercise three times a week, one that walked on a treadmill three times a week, one that did both types of exercise and one that did neither.

After six months, researchers found older adults who had done combined resistance and aerobic exercise had lower levels of insulin resistance, an age-related condition that often precedes diabetes, stroke and heart disease.

Participants in all of the exercise groups were better able to do simple tasks like standing up from a chair or walking in place, Davidson and colleagues wrote in the Archives of Internal Medicine. But here too, the group that did a combination of exercises fared best.

Dr. William Hall, director of the Centre for Healthy Aging at Highland Hospital in Rochester, New York, said bias against older people may be keeping some seniors from exercise.