Doing extreme endurance exercise, like training for a marathon, can damage the
heart, research reveals.
MRI scans on 40 athletes training for challenging sporting events like
triathlons or alpine cycle races showed most had stretched heart muscles.
Although many went on to make a complete recovery after a week, five showed
more permanent injuries.
The researchers told the European Heart Journal how these changes might cause
heart problems like arrhythmia.
They stress that their findings should not be taken to mean that endurance
exercise is unhealthy.
In most athletes, a combination of sensible training and adequate recovery
should cause an improvement in heart muscle function, they say.
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My personal feeling is that extreme endurance exercise probably does cause
damage to the heart in some athletes
Professor Sanjay Sharma Medical director of the London Marathon
But they believe more investigations are now needed, since their small study in
Australia did not look at any associated health risks.
Extreme training
The medical director of the London Marathon, Professor Sanjay Sharma, agreed
that more research was needed and said the results provided "food for thought".
"My personal feeling is that extreme endurance exercise probably does cause
damage to the heart in some athletes. 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.
And Doireann Maddock of the British Heart Foundation said the findings should
not put people off doing exercise.
"It is important to remember that the health benefits of physical activity are
well established. The highly trained athletes involved in this study were
competing in long distance events and trained for more than 10 hours a week.
"Further long-term research will be necessary in order to determine if extreme
endurance exercise can cause damage to the right ventricle of the heart in some
athletes. Any endurance athletes who are concerned should discuss the matter
with their GP.''
In the study, the scientists studied the athletes a fortnight before their
races, immediately after their races and then about a week later.
Immediately 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 - appeared dilated and didn't work as well as 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 returned 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 remained impaired compared with the pre-race readings.