Exercising about 75 minutes a week may be enough to improve fitness levels in inactive women who are overweight, researchers say.

The U.S. Centers for Disease Control and U.S. National Institutes of Health recommend at least a half hour on most days a week of moderate exercise to reduce the risk of heart disease, stroke and cancer. 

'Even a little is good; more may be better!'— I-Min Lee of Harvard Medical School summarizing study on the fitness benefits of physical activity

Dr. Timothy Church of Louisiana State University in Baton Rouge and his colleagues set out to look at the effects of exercising 75 minutes a week, 135 minutes a week or 190 minutes a week — half, the same and 150 per cent of the recommended amount.

"This information can be used to support future recommendations and should be encouraging to sedentary adults who find it difficult to find the time for 150 minutes of activity per week, let alone 60 minutes per day," the researchers wrote in Wednesday's Journal of the American Medical Association.

Surveys suggest about one in five adults in the U.S. report no physical activity, and lack of time is the major reason they give.

The researchers studied 427 overweight women with high or borderline-high blood pressure who had an average age of 57. Participants were randomly assigned to not exercise or to do one of the three levels of moderate intensity physical activity, by walking on treadmills or riding stationary cycles, three or four times a week.

"The lowest exercise dose, the 75 minute a week group, actually not only did not lose fitness, but they actually gained fitness during the six months, and that's an exciting result — that 75 minutes a week produces significant health benefits," Church said in a release.

Slimmer waists

All of the women who exercised were fitter based on measurements of oxygen intake during exercise, and their waists were smaller. That is important because belly fat increases the risk of premature death, Type 2 diabetes, cholesterol problems and hypertension.

None of the women in the exercise groups showed significant changes in blood pressure values or weight after six months compared with the control group, although the study was not designed for weight loss.

The more women exercised, the more they improved their physical fitness, the researchers found. They did not recommend lowering public health guidelines for physical activity, but suggested taking the results into account as revisions are developed.

Given cost and feasibility concerns, the trial used three patterns of physical activity, while in real life there are infinitely more, I-Min Lee of Brigham and Women's Hospital and Harvard Medical School in Boston, said in a journal commentary.

"The study by Church et al does provide important information on the dose of physical activity to improve physical fitness, a strong predictor of chronic disease and premature mortality," Lee wrote.

"This may be succinctly summarized for patients and clinicians as 'Even a little is good; more may be better!'"