New research finds that exercise not only reshapes your body's muscles but also your heart's muscles.

The study, published in the Journal of Applied Physiology, found that exercise can reshape the heart's ventricles, but the benefits depend on how much exercise is undertaken.

Researchers from Massachusetts General Hospital found that endurance athletes increased the size of both the left and right ventricles of their hearts after 90 days. But athletes who only strength-trained had growth in their left ventricle, but not the right.

Dr. Aaron L. Baggish of Mass General and colleagues studied 40 endurance athletes and 24 strength athletes. The endurance athletes were male and female long-distance rowers and the strength althletes consisted of male football players.

The endurance athletes showed enlargement and more efficient contraction and relaxation in both of the lower chambers of the heart. But the strength-trained athletes only had excessive growth in the muscle of the left ventricle.

The authors said the findings dispel the belief that the best athletes are those born with larger hearts. Instead, it demonstrates that the training itself is responsible for the enlarged or so-called "athelete's heart," which is responsible for above-average athletic performance, but has been linked to sudden cardiac arrest in young athletes.

Click here for more on this study published in the Journal of Applied Physiology.