The results of a new study may help explain why women’s hearts benefit more from physical exercise than men’s hearts do. Studies in exercising male and female mice found that moderate, long-term exercise provokes a sex-dependent cardiac change that is different for females.

The findings, reported at an American Physiological Society-sponsored meeting in Austin, Texas, may eventually lead to improved treatment strategies for women and men with heart disease.

Dr. Sebastian Brokat and colleagues from the Center for Cardiovascular Research, Charite Berlin, had male and female mice exercise for a little more than 5 weeks and they looked for structural and physiological changes in the animal’s hearts in response to the physical activity.

They found that regularly exercising female mice showed a much higher level of exercise performance than their male counterparts. Compared with male mice, female mice ran on a running wheel farther, faster, and for longer periods of time.

“Surprisingly,” Brokat said, the female mice developed bigger and stronger hearts than the male mice. This type of beneficial heart enlargement or “hypertrophy” frequently occurs with exercise. It differs from pathological hypertrophy, an abnormal enlargement that leads to problems such as heart failure, which is irreversible.

The study also found that only the female mice experienced a 20-percent decrease in a protein that is usually found in people with heart disease. “Also, a certain marker of fibrosis, which is normally increased in heart disease, was decreased in our exercising females compared to exercising males,” Brokat noted.

Heart enlargement in the exercising female mice was inversely correlated with decreased expression of these two protein markers.

It is possible that women have a lower level of these two markers of heart disease to start with, Brokat noted.

While more research is needed, the current findings, Brokat concluded, “bring us a step closer to explaining the sex bias in physical activity that protects the heart.”