Health

Marathon runners and others engaging in extreme endurance exercise may temporarily damage the right ventricle of their hearts, researchers found.

The impact on the ventricle, one of the four chambers involved in pumping blood around the body, was reversed after a week in most of the 40 athletes who took part in a study published in the European Heart Journal.

Five of them, however, showed more lasting damage, the researchers found.

Lead researcher Dr Andre La Gerche, from the University of Melbourne, Australia, said: 'Our study identifies the right ventricle as being most susceptible to exercise-induced injury and suggests that the right ventricle should be a focus of attention as we try to determine the clinical significance of these results.

'Affected athletes may be at risk of reduced performance - a cardiac 'over-training' syndrome - or it may cause arrhythmia (erratic heart beats).'

They found that in most athletes, "the heart rebuilds in a manner such that it is more capable of sustaining similar exercise stimulus in the future", Dr La Gerche, who is currently based at the University Hospitals Leuven in Belgium, said in a statement.

"The question is whether there are some athletes in whom extreme exercise may cause injury from which the heart does not recover completely."

The study participants trained for more than 10 hours a week and had no known heart problems. They agreed to undergo magnetic resonance imaging, blood tests and echocardiography a few weeks before the race, immediately after the event and six to 11 days later.

Right after the race, the athletes' hearts had changed shape, with volume increasing and the function of the ventricle decreasing, the study found.

The five athletes whose hearts had not fully recovered in the last test showed signs of scarring known as fibrosis, and they had been training and competing for longer than the others, the researchers said.

The findings should not be seen as an indication that endurance exercise is unhealthy, the researchers wrote.