Aug 22, 2014 04:36 AM EDT By Staff Reporter, UniversityHerald Reporter

Older women can engage in intense physical activity to lower the chances of developing life-threatening irregular heartbeat, according to a study by the Stanford University School of Medicine.

The researchers said that post-menopausal women, who were most physically fit, had 10 percent lower risk of developing Atrial Fibrillation (AF) compared to those with low levels of physical activity, even if they were obese. Obesity is an important risk factor for AF.

"We found the more physically active the women were, the less likely it was that they would develop atrial fibrillation," said Marco V. Perez, M.D., lead author of the study and independent instructor in cardiovascular medicine and director of the Inherited Arrhythmia Clinic, in a press release. "Also, the more obese the women were, the more they benefited from having greater degrees of physical activity."

For the study, the researchers surveyed over 81,000 post-menopausal women, aged 50-79 years, about their physical activity routine including how often they walked outside for more than 10 minutes daily or how often they indulged in exercise hard enough to sweat.

After 11 years, the researchers found that the most physically active women (those who exhausted more than 9 MET hours per week) had a 10 percent lower risk of developing AF compared to those who didn't walk outside for 10 minutes at least once each week.

MET measures the amount of energy used during physical activity. 9 MET hours per week is the result of walking briskly for 30 minutes everyday or bicycling at a normal pace for an hour twice a week.

Moderately physically active women (those with less than 3 MET hours per week) were associated with six percent lower risk of developing AF. Walking briskly for 30 minutes twice a week provide the benefit.

Women who were involved in energetic physical activity for more than 15 MET hours per week had a 9 percent lower risk of developing AF. This was the equivalent of running two hours a week.

Previous research showed that vigorous exercise might increase the risk for AF, but "there shouldn't be concerns about these degrees of exercise and AF in older women," Perez said.

The finding is published in the Journal of the American Heart Association (JAHA).

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