Changes to the heart linked to marathon running vary by age, sex, and training level, finds a synthesis of the available data, published in the open access journal BMJ Open Sport & Exercise Medicine.
But it's not clear if these changes represent normal physiological responses to endurance exercise or whether they are long term (mal)adaptations, the findings indicate.
It's known that both low and extremely high levels of exercise may increase the risk of death, note the researchers. And endurance exercise induces acute changes in heart function and increases in substances, such as enzymes and proteins, indicative of tissue damage and inflammation, they add.
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 isn't clear, they point out.
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 3 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 3 biomarkers were: cardiac troponin T(cTnT); cardiac troponin I (cTnI); and N-terminal proB-type natriuretic peptide (NT-proBNP).
Some 69 studies, comprising 3274 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 3 biomarkers were consistently raised within the first hour after finishing a marathon, exceeding commonly used clinical thresholds for myocardial injury, restricted blood supply (ischaemia), or heart failure.
Various changes to the chamber volume and pumping dynamics of the heart also occurred after running a marathon, including 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, say the researchers.
There were no other evident MRI changes to any of the other functions measured, suggesting marathon running doesn't induce any visible signs of clinically relevant structural myocardial injury, say the researchers.
Biomarker changes and echocardiography findings varied by performance running times, age, sex, and training level.
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. What's more, training status, a potentially influential factor, wasn't consistently reported across the included studies either.
And many of the studies included in the review 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," point out the researchers.
"The potential for pathological consequences in susceptible individuals or with repeated participation in extreme endurance events remains," they add.
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 remodelling," they conclude.
