June 11, 2026, 11:34 am | Read time: 6 minutes
Most people view marathons with a mix of fascination and skepticism. There is a persistent concern that such exertion may harm the body, particularly the heart, more than it benefits. A review of over 60 studies now shows: Within the first hour after a marathon, certain heart biomarkers rise to levels typically seen in a heart attack. However, researchers found no evidence that the heart suffers long-term damage.
Heart Biomarkers Spike After the Run–But No Visible Damage
According to various studies, there are about 0.5 to 2 deaths due to sudden cardiac death or a sudden acute cardiac event per 100,000 runners.1,2 Even though the risk for an individual is negligible, a marathon remains a physiological exception for the heart. Therefore, science is searching for ways to better predict for whom the 26.2 miles are a healthy challenge and for whom they are an overload.
A team led by Inarota Laily, who has been studying the effects of marathon running on the heart health of amateur athletes at the Amsterdam University Medical Center for years, has now conducted a comprehensive meta-analysis. The journal BMJ Open Sport & Exercise Medicine reports on the findings.3 According to this, a marathon leads to a massive increase in biomarkers that usually do not bode well. However, the researchers did not find visible signs that the heart is damaged by this.
Who and What Was Studied?
The researchers evaluated a total of 69 studies with 3,274 participants. The runners studied were between 27 and 63 years old, mostly men (73 percent), and had varying training conditions or marathon target times. Unfortunately, the exact training status was not consistently documented in many of the original studies.
Protein Levels Partly Above Clinical Thresholds
The researchers wanted to know what happens in and to the heart before and directly after the marathon.
- In the participants’ blood, they specifically looked for three substances that indicate stress or damage to the heart muscle. The proteins Troponin T (cTnT) and Troponin I (cTnI) are usually released when the heart muscle is damaged. Doctors use them to diagnose a heart attack. The marker NT-proBNP indicates the stretching and stress of the heart walls.
- Ultrasound provided information about the function of the heart valves and how well the heart chambers pump blood.
- Structural injuries or inflammation in the heart muscle tissue (myocardium) were detected using cardiac MRI.
Key Findings: Troponin at Heart Failure Levels Within 1 Hour Post-Run
One of the most striking findings is that the three biomarkers studied (Troponin T, Troponin I, and NT-proBNP) increased in all participants within the first hour after crossing the finish line. These values were so high that they exceeded the usual clinical thresholds for heart muscle damage, circulatory disorders, or even heart failure.
Heart Stress Significantly Higher in Full Marathon
The marathon represents a “stress threshold” for the heart, beyond which certain markers rise disproportionately, as particularly shown by a 2018 study by Prof. Dr. Juan Del Coso from the University of Madrid.4 Blood samples were taken ten minutes after the race, revealing that troponin levels rise even in 10-km runs and half-marathons. However, markers for the stretching of the heart walls were significantly elevated only in marathon runners. “Our results suggest that running shorter endurance races reduces heart muscle stress during the competition,” Del Coso said at the time. The current meta-analysis confirmed this connection.
No Signs of Heart Muscle Damage
Despite the alarming blood values, the cardiac MRI examinations in the meta-analysis provided a reassuring result: There were no visible signs of clinically relevant structural damage to the heart muscle. This means that while the heart is under massive stress, it seems to (at least in the short term) sustain no lasting tissue damage.
Event Clustering Especially in Men Over 35
The meta-analysis further shows that the heart’s response is significantly influenced by factors such as age, gender, specific training status, and of course, running time. Historical data supports this: A large portion of heart incidents during sports occurs in marathon competitions, with male runners over 35 being particularly affected. For this group, the question of whether the massive biomarker increases after the race are harmless adaptations or warning signals is of particular clinical importance.
Background: Sudden Cardiac Death in Athletes.
According to the Heart Foundation, in people under 35, diseases of the heart muscle, heart valves, aorta, and coronary arteries are possible triggers. At rest, these conditions usually cause no symptoms. When athletes exert their bodies heavily, dangerous heart rhythm disturbances can occur, leading to death. In athletes over 35, coronary artery disease is the most common cause of sudden cardiac death, accounting for about 80 percent.5
Performance
In addition to age and gender, changes in biomarkers and heart functions are directly dependent on the running time achieved. Those who run faster or push closer to their personal limits provoke stronger fluctuations in heart values in the blood.
Higher Training Volume Does Not Protect Against “Marathon Effect”
Interestingly, even the higher training volume of marathoners did not protect against the massive increase in stress markers–the marathon remains a stress situation for the heart that cannot simply be neutralized by more miles. An example is the 2018 study. Participants in the marathon group trained significantly more, about 25 miles per week, than the 10-km runners, who trained about 15 miles per week. Nevertheless, certain stress markers were significantly elevated only in marathon runners.
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Limitations
The researchers noted that women are underrepresented in the current data, and their hearts may respond differently to the stress of marathon running. This is not reflected in the current data. A crucial factor for heart stress is prior training. In many of the 69 analyzed studies, the training status of participants was not consistently recorded, making precise comparisons difficult. Many of the individual studies included in the meta-analysis had a high risk of bias, affecting the methodological quality of the research. While the meta-analysis shows that markers rise within the first hour, detailed longitudinal data over longer periods after exertion are often lacking to document full normalization. Finally, it must be mentioned that the studies cannot yet predict which particularly susceptible individuals might face pathological consequences from participating in extreme endurance events.
Conclusion
A marathon physiologically puts the heart in a state that would trigger alarms in a hospital, but modern imaging techniques show that the organ usually withstands this “storm phase” without visible structural injuries. Overall, a man over 35 who runs a marathon despite good training can expect higher stress levels and more pronounced (albeit mostly harmless) changes in pump function than younger runners or those on shorter distances.
The big question remains whether frequent repetitions over the years could lead to pathological changes. Therefore, scientists wish for better-designed long-term studies with more diverse participant groups to conclusively assess the actual health impacts of marathon running.