HMN 2026: How A marathon can send heart warning signals soaring, but what those alarms really mean is far from settled

Changes to the heart linked to marathon running vary by age, sex and training level, finds a synthesis of the available data, published in BMJ Open Sport & Exercise Medicine. But it is not clear whether these changes represent normal physiological responses to endurance exercise or long-term maladaptations, the findings indicate.

It is known that both low and extremely high levels of exercise may increase the risk of death, and endurance exercise induces acute changes in heart function and increases in substances, such as enzymes and proteins, indicative of tissue damage and inflammation, the researchers note.

But whether these changes are normal, transient physiological responses to the extra demands put on the heart under these conditions or early indicators of potentially harmful long-term adaptations is not clear.

How the review was done

To shed further light on the issue, the researchers scoured research databases for relevant studies published in English up to April 2025, each of which compared the effects of marathon running on the heart before and after the event.

The researchers looked in particular at three biomarkers indicative of heart wall stress or damage to the myocardium, the middle layer of the heart wall; ultrasound scan results of the heart’s structure, valves and pumping chambers (echocardiography); and cardiac MRI findings.

The three biomarkers were cardiac troponin T (cTnT); cardiac troponin I (cTnI); and N-terminal proB-type natriuretic peptide (NT-proBNP).

What the analysis found

Some 69 studies, including 3,274 mostly male (73%) participants between the ages of 27 and 63, were eligible for systematic review, and 49 were included in the pooled data analysis.

The analysis showed that all three biomarkers were consistently raised within the first hour after finishing a marathon, exceeding commonly used clinical thresholds for myocardial injury, restricted blood supply (ischemia) or heart failure.

Various changes to chamber volume and the pumping dynamics of the heart also occurred after running a marathon, including in the left ventricular ejection fraction, a measure of the amount of blood pumped out of the heart’s main pumping chamber, the left ventricle, with each beat.

But these changes were minor and fell outside the range of what would commonly be interpreted as clinically meaningful, the researchers say.

There were no other evident MRI changes to any of the other functions measured, suggesting marathon running does not induce any visible signs of clinically relevant structural myocardial injury, the researchers say.

Biomarker changes and echocardiography findings varied by performance running times, age, sex and training level.

Limits and unanswered questions

The researchers acknowledge various limitations to their findings.

Notably, most of the study participants were men, and women might have different cardiovascular responses to marathon running, both in the short and long term, they say. Furthermore, training status, a potentially influential factor, was not consistently reported across the included studies either.

Many of the studies included in the review also scored high on the risk of bias, indicating room for methodological improvement, they add.

“Our pooled findings confirm and quantify previously reported post-marathon elevations in cardiac biomarkers and alterations in ventricular function. However, the clinical relevance of these changes remains unclear,” the researchers point out.

“The potential for pathological consequences in susceptible individuals or with repeated participation in extreme endurance events remains.”

Well-designed long-term studies in diverse groups, to include sex and ethnicity, are needed to find out “whether these effects represent physiological responses to extreme levels of exercise or reflect early markers of pathological cardiac remodeling,” they conclude.

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