Jogging may be okay, but going for extreme endurance events such as marathons could take a toll on your health, says a new study. It's said that putting the heart under heavy strain for long periods causes scarring of the heart muscle, known as fibrosis. This damage is normally reversed within a week of an event, the process of repairing serving to make the heart fitter. However, researchers who followed 40 elite Australian athletes have found evidence of "more permanent damage" in five of them, the European Heart Journal reported. According to them, fibrosis can impair how well the heart performs when a person is exercising intensively. It can also lead to irregular heartbeats, called arrhythmias. And serious arrhythmias can be life-threatening. The lead researcher at a hospital in Belgium said: "It is likely to affect only a minority of athletes, particularly those in whom more intense training fails to result in further improvements in their performance." He said that the five who saw longer-term damage had been training and competing for longer than the others. "It is most important that our findings are not over-extrapolated to infer that endurance exercise is unhealthy. Our data do not support this premise," he added. The researchers found damage in the right ventricle, one of the four chambers of the heart, using MRI scanning. They found no damage in the left ventricle. However, experts are fully convinced. A consultant cardiologist and medical director of the London Marathon, was quoted by The Daily Telegraph as saying, "it is too early to say that taking part in endurance sports causes long-term damage to the right ventricle." But, this study is an indication that it might cause a problem in some endurance athletes with a predisposition and, therefore, it should be studied further, he added.