Can Too Much Exercise Harm the Heart?
by Larry Creswell, M.D.
Can too much exercise harm the heart? It’s an interesting question -- and probably an important question for many of the readers here at Endurance Corner. This question has received attention recently because of news reports in the popular press , so I thought I’d review the available data, offer some of my own thoughts and conclusions, and let you decide for yourself if you can have “too much of a good thing.”
An article written by Jonathan Knowles in the online edition of the New York Times (NYT) on March 9, entitled “When Exercise is Too Much of a Good Thing” caught my eye. Judging from the questions I received in the following week -- and more than a little discussion among fellow athletes and colleagues since then -- the article caught the eye of a good many athletes. Knowles shared the findings of a couple recent scientific studies that raise the possibility that significant damage to the heart might occur with long-term participation in endurance-type athletics.
Some Important Observations
Until recently, though, it hasn’t been possible to examine patients (or animal subjects) for very small areas of heart muscle fibrosis except at autopsy. For that reason alone, the hypothesis remained conjecture. New and continued development of cardiac magnetic resonance imaging (MRI) has changed all that. With the use of the intravenous contrast agent, gadolinium, a technique known as late gadolinium enhancement (LGE) can be used to detect very small areas of fibrosis within the walls of the beating heart. This is a technique that can now be used experimentally as well as clinically.
The Scientific Studies
A more recent study was mentioned in the NYT article. In this report (Wilson M, O’Hanlon R, Prasad S, et al.), Wilson and colleagues from the U.K. describe a cardiac MRI study of 12 lifelong male veteran endurance athletes (50 to 62 years old) and 20 age-matched control subjects. The veteran athletes reported a continuous history of endurance athletics of between 35 and 52 years at the time of enrollment into the study. Indeed, the participants were recruited from a running club whose membership required completion of 100 marathons. These investigators found abnormal heart fibrosis in 50% of the athletes and in none of the control subjects. They concluded that additional well-controlled studies are needed to determine if certain individuals are placing themselves at undue risk with lifelong participation in endurance sports.
The last study we’ll consider today was conducted by Benito and colleagues in Barcelona and reported earlier this year in the prominent journal Circulation (Benito B, Gay-Jordi G, Serrano-Mollar A, et al., 2011). These investigators established a rat model of long-term exercise, where the animals ran vigorously for periods of up to 16 weeks (perhaps 10 years on a human scale). They found that over the 16-week period, the rats developed fibrosis of the heart walls that was similar to the findings reported from the cardiac MRI studies above. It also turned out that the animals with the abnormal fibrosis were also more likely to have inducible arrhythmias. Perhaps most interestingly, they found that during an eight-week period of rest after the exercise period, that the fibrosis disappeared.
Some Thoughts on the Evidence
Here’s my take. I started the year here at Endurance Corner with a column devoted to the health benefits of exercise. These benefits are simply undeniable. Nobody should stop exercising. Is it possible that too much exercise can harm the heart? I think the answer is yes. The scientist in me recognizes that there can be “too much of a good thing” in almost all biological and physical systems. Exercise and the heart should be no different. There may well be some threshold of accumulated exercise, beyond which there is heart damage. The recent studies that I’ve mentioned above make some interesting and preliminary observations that warrant further study. With millions of athletes in this country alone participating in endurance sports, we deserve to learn more about the long-term consequences to the heart of those activities. For the moment, though, there just isn’t enough information available to dissuade me (or make recommendations to other endurance athletes) to stop exercising. We’ll stay tuned for more information as it becomes available.
Breuckmann F, Mohlenkamp S, Nassenstein K, et al., (2009). Myocardial late gadolinium enhancement: Prevalence, pattern, and prognostic relevance in marathon runners. Radiology 2009; 251:50-57.
Wilson M, O’Hanlon R, Prasad S, et al., (n.d.). Diverse patterns of myocardial fibrosis in lifelong, veteran endurance athletes. J Apppl Physiol (in press, published online in advance).
Larry Creswell, M.D., is a cardiac surgeon and Associate Professor of Surgery at the University of Mississippi Medical Center in Jackson, Mississippi. In addition to his regular column on Endurance Corner, he maintains The Athlete's Heart blog to offer information about athletes and heart disease in an informal way and to encourage exchange and discussion that will help athletes build a heart-healthier lifestyle. You can contact him at firstname.lastname@example.org.