Strenuous exercise, such as running a marathon, can temporarily damage heart muscle, according to a new study. But fortunately being better trained for running fast for long periods of time can reduce that risk.

Research from the Quebec Heart and Lung Institute at Laval University found that strenuous exercise can cause inflammation of the heart, especially among runners with lower fitness and less training. The study followed 20 marathon runners between the ages of 18 and 60. The participants were evaluated before and shortly after the Quebec City marathon, and three months later. While the runners trained, researchers led by Dr. Eric Larose used MRIs and blood tests to keep track of their heart function.

After the marathon, half of the runners showed a functional decline in both the left and right ventricles of the heart. In some, there was swelling and a decrease in blood flow in certain areas of the heart. Larose found that those who were less fit were more likely to experience this decline in function. “When you don’t train as you should, you are going to get these changes,” he said. A similar study conducted in 2011 showed that extreme endurance exercise could temporarily damage the right ventricle of the heart, but not the left ventricle.

Of course, the study isn’t meant to alarm people, especially those running to stay fit and healthy. The benefits of running far outweigh any temporary damage that might occur in the heart muscle. The damage isn't permanent, Larose stresses. Besides, those who are more fit and who have more training under their belts are less likely to experience this temporary inflammation, and are more likely to benefit from the long-term effects of aerobic exercise.

“I don’t think it is reason for concern,” Dr. James Eichelberger, associate professor of cardiology at the University of Rochester School of Medicine and Dentistry, told HealthDay. “There is little risk. If you want to avoid that, exercising less vigorously for a less amount of time makes some sense.”

However, it’s important to note that while exercise is good, there may be a limit, or a point at which the benefits begin to plateau. “Habitual physical activity reduces coronary heart disease events, but vigorous activity can also acutely and transiently increase the risk of sudden cardiac death and acute myocardial infarction in susceptible persons,” authors of a 2007 study write. Also noted in the study is that habitual physical activity reduces the risks of fatal and nonfatal coronary artery disease (CAD) events, and that benefits of regular exercise outweigh its risks. Performing mild exercise, like the 30 minutes per day of walking recommended by the Centers for Disease Control and Prevention, can help people reach a moderate level of fitness without the rare risks of heart inflammation, enlargement, or scarring.

 

Sources: Gaudreault V, Tizon-Marcos H, Poirier P, Pibarot P, Gilbert P, Amyot M, Rodés-Cabau J, Després JP, Bertrand O, Larose E. Transient myocardial tissue and function changes during a marathon in less fit marathon runners. Can J Cardiol. 2013.

Thompson PD, Franklin BA, Balady GJ, Blair SN, Corrado D, Estes NA 3rd, Fulton JE, Gordon NF, Haskell WL, Link MS, Maron BJ, Mittleman MA, Pelliccia A, Wenger NK, Willich SN, Costa F; American Heart Association Council on Nutrition, Physical Activity, and Metabolism; American Heart Association Council on Clinical Cardiology; American College of Sports Medicine. Exercise and acute cardiovascular events placing the risks into perspective: a scientific statement from the American Heart Association Council on Nutrition, Physical Activity, and Metabolism and the Council on Clinical Cardiology. Circulation. 2007.