Researchers from Mass. General Hospital and the Harvard University Health Services have found that intense exercise can significantly change the function and structure of the heart.

“I’ve been doing work with athletes now for about six years,” said Malissa J. Wood, the senior author on the study and a professor at Harvard-affiliated Mass. General. “[And in my work] there has been this long-questioned concept of the athlete’s heart. Did the athlete always have that type of heart, or did it occur by training?”

In order to discover the causes of how athletes’s hearts allow them to surpass normal physical limitations, the research team devised a study consisting of male and female Harvard rowers and male Harvard football players.

“We studied both the rowers and the football players over the course of their training season,” Wood said.

The rowers were chosen to represent endurance exercise and the football players were chosen to represent strength exercise. Endocardiography studies—ultrasound pictures of the heart’s structure and function—were taken at the beginning of the training and at the end.

At the end of the training period, they found that overall the size of each athlete’s heart increased, though for the rowers the increase was found in the left and right ventricles, and for the football players in the thickness of the heart.

The most significant difference was found in the relaxation of the heart muscle between beats. Though all results remained in normal ranges, this relaxation increased for the rowers and decreased for the football players.

“We were surprised because we didn’t expect to see such different changes between the athletes,” Wood said.

Aaron L. Baggish, a fellow at Mass. General’s cardiology division, said that the study shows a difference in the results of two types of athletics.

“The functional differences raise questions about the potential impact of long-term training,” Baggish said.

Applying the results to cardiovascular treatment, Baggish added: “The take-home message is that, just as not all heart disease is equal, not all exercise prescriptions are equal. This should start us thinking about whether we should tailor the type of exercise patients should do to their specific type of heart disease.”

The study, which was published in the Journal of Applied Physiology, has already prompted further research by Wood and her collaborators.

“We want to be able to develop a fitness index,” Wood said. “We want to get the peak fitness for an athlete individually.”

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