Fitness health centre

Does running marathons damage the heart?

By Lilian Anekwe

BMJ Group News

What do we know already?

There’s lots of evidence that regular exercise is good for you. But there is some evidence that high-intensity endurance exercise could cause mild damage to one part of the heart, the right ventricle. This is one of four chambers in the heart, and receives blood from the body before pumping it towards the lungs.

But much of what we know is based on studies on animals, and mostly rats. We still don’t know if intense endurance exercise damages the right ventricle more than other parts of the heart, how long the damage lasts and if it has any effect on people’s long-term health.

This small study looked at 40 athletes who took part in one of four increasingly intense physical events: a marathon, a triathlon, an alpine cycling race, and an ultra-triathlon (a triathlon over longer distances). All the athletes had a very high level of fitness and did more than 10 hours of intense training a week, were high-performers that had finished in the top quarter in a recent event, and had no symptoms or factors that would put them at risk of heart damage.

The athletes had a variety of tests on their heart two or three weeks before their event, within one hour of their event, and six to 11 days after their event, during which time the athletes did only very light training. The researchers then compared the results of the tests to see if any damage to the heart occurred and how long it lasted.

What does the new study say?

All the tests showed the functions of the right ventricle worked less well after their event compared with before it.

Tests using a technique called echocardiography, which uses sound waves to build up a picture of the heart, showed that after completing their events, athletes’ pumped out 9% less blood from the right ventricle compared with before their event.

The tests also showed the chambers in the heart had become larger, and blood tests after the event showed an increase in levels of a substance called B-type natriuretic peptide (BNP), which is produced by the ventricles when the heart muscle is stretched.

The athletes also had a test called a magnetic resonance imaging (MRI) scan, which uses a magnetic field to create a detailed picture of the inside of their heart. The MRI scans showed that some scarring occurred to the heart muscle in the right ventricle in five athletes after completing their event.

The changes were most pronounced in athletes who competed in the longest endurance event, the ultra-triathlon. But even in this group the heart had recovered within one week. The changes did not occur in the left ventricle, which the researchers also tested for comparison.