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?
Reassurance comes from a new ten-year study of 152 recreational marathon runners, published in Jama Cardiology. Researchers examined 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 immediately after races, it recovered within days. Crucially, over ten years, there was no sign of lasting damage to heart function.
This matters because earlier studies raised concerns that endurance exercise might harm the heart. Much of that worry came from blood tests taken after races. Many runners show raised levels of troponin, a substance released when heart muscle cells are under strain.
Troponin is normally used to help diagnose heart attacks, so seeing it rise after a marathon can look alarming. But context matters. In hospitals, troponin levels are interpreted alongside symptoms, heart tests, and scans. After endurance exercise, troponin often rises even when there is no sign of blocked arteries or lasting heart damage.
Studies show that many healthy runners exceed standard troponin cut-offs after races despite normal heart scans and no symptoms. The rise appears to reflect temporary stress on heart cells rather than permanent injury. Imaging studies show short-term changes in how the heart fills or pumps blood, which settle with rest.
The right side of the heart seems particularly affected. During sustained exercise, pressure in the lungs rises sharply, placing extra strain on the right ventricle. Several studies show it becomes temporarily enlarged and less efficient immediately after long races, before returning to normal.
What the new study adds is reassurance that these repeated short-term stresses do not inevitably cause long-term harm 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 risk-free. Marathon running can expose previously undiagnosed heart disease, especially coronary artery disease. Chest pain, breathlessness or collapse during or after exercise must never be dismissed simply because someone is fit. In people with symptoms, raised troponin levels usually point to a very different and more serious problem.
Deaths during marathons are rare — about one per 100,000 runners — and the risk has fallen as race medical care has improved. When sudden cardiac arrest occurs, it is usually linked to underlying heart disease rather than damage caused by running itself.
There remains debate about very high-level endurance exercise. Some studies of athletes who have trained intensely for decades show small areas of heart scarring, linked to abnormal heart rhythms. These findings are uncommon, vary widely between individuals and appear influenced by genetics, training volume and intensity.
Taken together, the evidence suggests that for most recreational marathon runners, the heart adapts rather than deteriorates. Temporary changes after races reflect hard work, not injury. Fitness brings resilience — but it does not replace the need for medical attention when warning signs appear.
The Conversation