People indulging in strenuous exercise, like training for a marathon may make them more susceptible to heart disease risk, a new study has revealed.
MRI scans on 40 athletes training for challenging sporting events like triathlons or alpine cycle races indicated that most of them had stretched heart muscles.
Although many completely recovered after a week but five showed more permanent injuries.
The researchers have pointed out that these changes might cause heart problems like arrhythmia.
They also insisted that their findings should not be misinterpreted that endurance exercise is unhealthy.
In most athletes, a blend of sensible training and adequate recovery should cause an improvement in heart muscle function.
"My personal feeling is that extreme endurance exercise probably does cause damage to the heart in some athletes," said medical director of the London Marathon, Professor Sanjay Sharma. I don't believe that the human body is designed to exercise for as long as 11 hours a day, so damage to the heart is not implausible."
But he said it was too early to say that taking part in endurance sports causes long-term damage, the BBC reported.
In the study, the scientists observed the athletes a fortnight before their races, immediately after their races and then about a week later.
Instantly after the race, the athletes' hearts had changed shape. The right ventricle - one of the four chambers in the heart involved in pumping blood around the body - seemed dilated and did not work like the way it had been in the weeks leading up to the race.
Levels of a chemical called BNP, made by the heart in response to excessive stretching, increased.
A week later, most of the athletes' hearts had reverted to the pre-race condition. But in five who had been training and competing for longer than the others, there were signs of scarring of the heart tissue and right ventricular function stayed impaired compared with the pre-race readings.