The study is among the first to examine how exercise can improve the quality of life of postmenopausal women who were extremely out of shape but otherwise healthy, said Dr. Timothy Church of the Pennington Biomedical Research Center in Baton Rouge, Louisiana.

"This is by far the largest exercise trial which has ever looked at quality of life," Church said in a telephone interview. The results, which were presented at the American Heart Association's Conference on Nutrition, Physical Activity and Metabolism in Colorado Springs, Colorado, update a 2007 study by Church and others in the Journal of the American Medical Association.

That study found women who exercised 10 to 30 minutes saw improvements in fitness. The latest findings look at other measures, such as mental health and social functioning.

The researchers studied 430 sedentary women past menopause with an average age of 57 who were assigned to one of three exercise groups: those who exercised 70 minutes a week; 135 minutes a week and 190 minutes a week.

A fourth group did not have an organised exercise program and served as a control group.

At the beginning of the study, the women were asked a host of questions about their health status, their physical health, including any pain or physical limitations, and their mental health, including whether they were nervous, depressed, peaceful or happy.

After six months, the researchers found women who participated in the highest exercise group saw the greatest improvements in most quality-of-life scales.

But even the women in the lowest exercise group saw significant improvements in general health, vitality, emotional health and social functioning.

"That's basically just 10 minutes of daily walking at a brisk pace," Church said of the low exercise group.

He said the women in the study only lost an average of 3 to 6 lbs (1.5 to 2.5 kg).

"These changes in quality of life were not driven by weight. These changes were driven by changes in activity," he said.