In most cases, the answer is no. However, researchers led by Andre La Gerche of the University of Melbourne have found that endurance exercise (marathons, alpine bike races and triathlons) can damage the right ventricles of a small subset of athletes. To be clear, this study did not address sudden cardiac arrest during a race, for which marathoners are at no greater risk than any other athletes. Rather it looked at whether asymptomatic damage could be detected in extreme athletes. The short answer is that although such damage does occur, it seems to be reversible for most people.
Forty experienced volunteers (having finished in the top 25% of a recently competed race) with no known heart problems were asked to run a race for science. Each person had complete heart work-ups a few weeks before the race, within an hour of finishing, and about a week later. The tests included cardiac MRIs, echocardiographs and blood tests.
Immediately after intense endurance exercise, the athletes did show changes in the shape and function of their hearts. Specifically, they had a significant reduction in function in their right ventricles, which was corroborated by biomarkers in the blood tests. The left ventricles did not appear to be affected, which was consistent with previous studies showing that the right ventricle is under greater stress than the left during intense exercise.
The good news is that for most of the athletes, that change was completely reversed by the one week follow up. Only one out of eight people still showed signs of damage at that time. And those people may have simply required a slightly longer recovery time.
The researchers are quick to point out that their small study in no way negates the positive effect of exercise on human health.
To draw an analogy, some tennis players develop tennis elbow. This does not mean that tennis is bad for you; rather it identifies an area of susceptibility on which to focus treatment and preventative measures.
So, to summarize, this study may just indicate that ultra-athletes should give their hearts time to recover between events. However, just to be on the safe side, I’ve decided to forego running marathons.