The review explores the impact of extreme endurance running on heart health

Changes in the heart associated with marathon running vary by age, gender and training level, finds a synthesis of available data, published in the open access journal BMJ Open Sport & Exercise Medicine.

However, it is unclear whether these changes represent normal physiological responses to endurance exercise or whether they are long-term (mal)adaptations, the findings show.

Both low and extremely high levels of exercise are known to increase the risk of death, the researchers note. And endurance exercise causes 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 additional demands of the heart under these conditions or early indicators of potentially harmful long-term adaptations is not clear, they point out.

To shed further light on the issue, the researchers searched research databases for relevant studies, published in English through April 2025, each of which compared the cardiac outcomes of marathon running before and after the event.

The researchers specifically looked at 3 biomarkers indicative of heart wall stress or damage to the myocardium, the middle layer of the heart wall. Results of an ultrasound scan of the structure of the heart, 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-like natriuretic peptide (NT-proBNP).

Approximately 69 studies, involving 3274 mostly male (73%) participants between 27 and 63 years of age, were eligible for systematic review and 49 were included in the pooled data analysis.

The analysis showed that all 3 biomarkers rose steadily within the first hour after finishing a marathon, exceeding commonly used clinical thresholds for myocardial injury, limited blood supply (ischemia) or heart failure.

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

But these changes were small and did not exceed the range of what would normally be interpreted as clinically significant, the researchers say.

There were no other apparent changes on MRI in any of the other functions measured, suggesting that marathon running does not cause visible signs of clinically relevant structural myocardial injury, the researchers say.

Biomarker changes and echocardiographic findings differed across run times, age, sex, and training level.

The researchers acknowledge several limitations to their findings. Notably, most of the study participants were men, and women may have different cardiovascular responses to marathon running, both short-term and long-term, they say. Furthermore, educational status, a potentially important factor, was not consistently reported in the included studies either.

And many of the studies included in the review scored high for risk of bias, indicating room for methodological improvement, they add.

“Our pooled findings confirm and quantify previously reported post-marathon increases in cardiac biomarkers and changes in ventricular function. However, the clinical significance 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,” they add.

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