Do marathons damage your heart? Decade-long study finally settles debate

By David C. Gaze for The Conversation

A marathon pushes the human body close to its limits. Legs tire, lungs burn and the heart works hard for hours on end. For years, that strain has raised an uncomfortable question: does running 26 miles actually damage the heart? The strongest reassurance comes from a new ten-year study of 152 recreational marathon runners, published in the journal Jama Cardiology. Researchers checked the runners’ hearts before and after races, then tracked their heart health over the next decade.

They found that although the heart’s right ventricle – the chamber that pumps blood to the lungs – showed a short-term drop in pumping ability straight after races, it recovered within days.

Crucially, over the ten-year follow-up period, there was no sign of lasting damage to heart function in these runners.

This finding is important because earlier studies had raised worries that long-distance exercise might damage the heart. Much of that concern came from blood tests taken after endurance events.

After a marathon, many runners show higher levels of a substance called troponin in their blood. Troponin is released when heart muscle cells are put under strain.

Doctors normally use troponin levels to help diagnose a heart attack. So seeing these levels rise after a race can look worrying and sometimes make it harder to tell whether someone is having a genuine medical emergency.

When troponin levels mislead. But context matters. In hospitals, raised troponin levels are only judged alongside symptoms, heart tests and scans. After long-distance endurance exercise, troponin often rises even when there is no sign of blocked arteries, a heart attack or lasting heart damage.

Studies show that many healthy marathon runners have troponin levels above the usual medical cut-offs after a race, despite normal heart scans and no symptoms of a heart attack.

This rise seems to reflect temporary strain on heart muscle cells, rather than permanent damage. Heart scans using ultrasound or MRI show that these changes are usually linked to short-term changes in how the heart fills or pumps blood, which settles with rest.

The right side of the heart seems particularly affected during marathons. It pumps blood through the lungs, where pressure rises sharply during sustained exercise. Several studies have shown that the right ventricle becomes temporarily enlarged and less efficient immediately after long races, before returning to normal.

What the new ten-year outcome study adds is reassurance that these repeated short-term stresses do not inevitably lead to long-term damage in most recreational runners.

Over a decade of marathon running, heart structure and pumping ability remained within normal ranges.

That does not mean endurance running is without risk. Marathon running can expose hidden heart disease, particularly coronary artery disease.

A tragic example was reported recently in the UK press, where a 42-year-old runner with chest pain was initially reassured and later died from a heart attack. In that case, the problem was not exercise-related troponin release but underlying coronary disease that was not identified as the cause of the elevated troponin.

This distinction is vital. Chest pain, breathlessness or collapse during or after exercise cannot be dismissed simply because someone is fit.

In people with symptoms, raised troponin levels usually signal a very different process than the benign rises seen after a marathon in otherwise well runners.

Deaths during marathons are very rare. Large studies suggest there is about one death for every 100,000 runners, and this risk has fallen over time as medical support at races has improved. When a sudden cardiac arrest does happen, it is usually linked to an undiagnosed heart condition, rather than damage caused by running itself.

Very high-level endurance exercise There is still a debate about very high-level endurance exercise. While most recreational runners show no lasting harm, some studies have found signs of scarring in the heart – called fibrosis – in athletes who have trained at very high volumes for many years.

Heart MRI scans have shown that many older endurance athletes have small areas of scar tissue in their heart muscle. In the recent Ventoux study – named after Mont Ventoux, one of the toughest climbs in the Tour de France – researchers looked at 106 male cyclists and triathletes over 50.

Almost half of these athletes had detectable scarring, compared with very few in non-athletic participants.

This scarring was linked to a higher chance of abnormal heart rhythms, including some that can be deadly. But serious problems are still rare, and results differ a lot between people, suggesting factors like genetics, training intensity and how long someone has trained all matter.

Taken together, the evidence suggests that for most recreational marathon runners, the heart adapts rather than deteriorates. Temporary changes after races and short-term rises in troponin reflect stress, not injury.

Being fit doesn’t mean you can’t develop heart disease, and test results only make sense when considered alongside symptoms and medical checks. The marathon runner’s heart is strong, but it still needs careful assessment.

For most recreational runners, the evidence is reassuring. The heart adapts to marathon running rather than breaking down under it. Those temporary spikes in troponin after races reflect hard work, not damage, and decade-long studies confirm that with proper training, the heart stays healthy.

But fitness isn’t immunity. Chest pain, unusual breathlessness or feeling faint during exercise always needs proper medical attention. The marathon runner’s heart is resilient – but it still deserves respect and careful monitoring.

(David C. Gaze is a senior Lecturer in Chemical Pathology, University of Westminster)