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July 18, 2025 — A new study has found that nearly half of veteran male endurance athletes have evidence of hidden heart changes that may significantly increase their risk of serious arrhythmias, even if they have no symptoms.
Key Findings
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Myocardial Fibrosis Prevalence: Cardiovascular MRI scans detected focal myocardial fibrosis—a type of scarring in the heart muscle—in 47.2% of asymptomatic male endurance athletes aged 50 and older. All participants had logged at least 10 hours of intense exercise weekly for more than 15 years.
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Risk of Ventricular Arrhythmia: Those with myocardial fibrosis faced a nearly fivefold higher risk of developing ventricular arrhythmias, according to the study’s hazard ratio calculations.
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Follow-Up Outcomes: Over a median follow-up period of nearly two years, 21.7% of the athletes experienced episodes of ventricular arrhythmia, and 2.8% developed sustained ventricular tachycardia, a potentially life-threatening condition.
Study Details
Researchers carried out a prospective observational study involving 106 asymptomatic male veteran cyclists and triathletes, all over 50, with no pre-existing cardiovascular conditions. Each participant underwent:
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Cardiac MRI, including late gadolinium enhancement for detailed tissue characterization
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Exercise testing
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Device-based heart rhythm monitoring through implantable loop recorders
The primary endpoint was the incidence of ventricular arrhythmia, monitored over a median period of 720 days.
Implications
These findings raise concerns about the “cardio-toxic” effects of long-term, intense endurance exercise on the heart, even among athletes with no outward symptoms. The myocardial fibrosis seen in these athletes was primarily nonischemic and mostly affected the basal inferolateral region of the left ventricle—a distribution pattern distinct from typical ischemic heart disease.
While endurance exercise is broadly associated with cardiovascular benefits, these results suggest that lifelong high-volume athletic training in men may make them more susceptible to arrhythmias caused by underlying, silent changes in heart muscle tissue. Medical experts caution that more research is needed before changes to exercise guidelines are considered for master athletes and recommend further monitoring in this population.
Disclaimer
This article is based on a summary of emerging research. The findings discussed require validation in future studies. The information provided here is not a substitute for professional medical advice. Please consult a healthcare provider for any heart health concerns or before making changes to your exercise regimen.
