Harvard athletes have the biggest muscles on campus and their hearts are no exception, according to a recent study that tracked the heart development of Harvard football players and rowers.

The findings, presented by researchers Massachusetts General Hospital and Harvard University Health Services, suggested that aerobic and endurance training can cause the chambers of the heart to enlarge, while short-burst activities can increase heart muscle mass by up to 12 percent.

Using ultrasound technology, researchers evaluated the heart structures of athletes belonging to the Harvard football team as well as the men and women’s crew teams at the beginning of the study and reassessed them after a three month period of “fairly intense training,” according to Research Fellow in Medicine Aaron L. Baggish, one of the study’s lead researchers.

“There were changes in [the heart structure of] almost every athlete,” said Baggish, a cardiologist at Massachusetts General Hospital.

But he also emphasized that one of the key results of the study is that “different types of training affect the heart in different ways.”

By the end of the fall season, many of the football players’ hearts had accumulated up to 12 percent more muscle mass due to a thickening of their heart walls. While the mass of the rowers’ hearts did not increase as significantly, the chambers of their hearts increased in size.

The Harvard researchers attributed the different forms of heart growth to the emphasis on endurance in the sport of crew as opposed to the short, but intense bursts of energy required in football.

“There’s a lot of explosiveness with the drills that we do,” said Harvard runningback Cheng Ho ’10. “I think it takes a lot out of you, and a lot of commitment...it does take a lot of heart.”

The study is part of an ongoing effort by Baggish and his colleagues to better understand the effects of athletic activity on the heart. As Baggish noted, their initial data does not address the long term impacts of athletics on the heart.

“In the long-term plan, we will see if most of the changes of the heart are in place by the time athletes arrive to college,” added Baggish.

Harvard running back Clifton G. Dawson ’07, who is training for the NFL draft, said heart was the bedrock of competition.

“During the course of the game, there are so many high points and low points, you need a strong heart to be able to focus and give it your all to win,” he said.