When we think of cardiovascular health, physical activity – such as running – often comes to mind. But new research shows that running a marathon can prompt heart muscle changes that cause the heart to swell, and this is particularly the case in runners with lower fitness levels.

The researchers, who reported their findings in the Canadian Journal of Cardiology, say previous studies have found that many sports competitors show signs of injury to the heart muscle and cardiac abnormalities after they exercise for long periods of time.

The new study was created to assess the degree to which running a marathon stresses the heart, and whether it might cause permanent damage.

As such, the researchers studied 20 amateur long-distance runners between the ages of 18 and 60, who were going to run in the Quebec City Marathon. The runners had no known cardiovascular disease and were not on any kind of drug treatment.

The researchers excluded any runners who had run a marathon in the 2 months before recruitment or during the study period.

Cardiac risk associated with running

Tested 6-8 weeks before the marathon and on the day of the race, the runners were also tested again within 48 hours of completing the marathon. This test included a second MRI and blood sampling.

The researchers say this timeframe ensured sufficient rehydration and a return to normal heart and blood pressure rates after the race. But importantly, it was short enough for them to observe any myocardial changes.

In half of the runners, researchers observed that the marathon prompted a decrease in left and right ventricular function. And when a lot of the heart was affected, there was swelling and reduced blood flow in the heart.

Dr. Eric Larose, of the Institut universitaire de cardiologie et de pneumologie de Québec (IUCPQ) in Canada, says that the heart muscle changes they observed were more common in runners who had lower fitness levels and who trained less.

But they also observed that these changes were temporary.

Dr. Larose says:

“Segmental function decrease is associated with poor prognosis in the presence of CAD (coronary artery disease) or cardiomyopathy. Segmental dysfunction also indicates a poor prognosis in adults without cardiovascular disease.

Although we don’t know whether such changes mean that recreational runners are at risk, the attendant edema, and reduced perfusion suggest transient injury.”