Exercise can cause structural changes in the heart, and these changes vary depending on the type of training an athlete is engaged in.
Small studies have found that the left ventricle, the heart's main pumping chamber, is larger in trained athletes, although there has been no research on how exercise affects the structure of the right ventricle. It is also unclear whether exercise itself changes the structure of the heart or whether individuals with unusually large left ventricles are more likely to become athletes.
To investigate, researchers in America studied 40 endurance athletes and 24 strength athletes, examining their hearts with echocardiography before and after 90 days of team training. The endurance group included male and female long-distance rowers, while the strength group consisted of male football players. It was found that while left ventricle mass increased in both groups, the endurance athletes also showed better diastolic function in their left ventricle, and enlargement and more efficient contraction and relaxation in both of the lower chambers of the heart, or atria. But the strength-trained athletes actually had hypertrophy, or excess growth in the muscle of the left ventricle, and reduced diastolic function, but no other structural changes.
The findings contradict the notion that people become competitive athletes due to their heart structure, and instead demonstrate that it is athletic training itself that is largely responsible for athlete's heart. The results also point towards the need of making tailored recommendations for rehabilitation and recreational exercise for people with heart problems.