Answer: The heart muscle of conditioned athletes enlarges and strengthens.
Increased cardiovascular fitness causes real physical changes in the structure of the heart. The muscles in the heart wall thicken, and the heart pumps more blood with each beat. That increased efficiency means an athlete's resting heart rate falls to a level that could indicate trouble in a nonathlete. Many athletes don't realize that high levels of conditioning also cause heart symptoms that doctors might mistake for serious problems.
