People who carry arrhythmogenic cardiomyopathy, an inherited heart condition, face a 58% higher likelihood of a dangerous ventricular arrhythmia if they train as endurance athletes than if they are sedentary or focus on strength training, according to a study published September 10, 2026 in JACC: Clinical Electrophysiology. The finding comes from a retrospective review of 355 participants in the Johns Hopkins Arrhythmogenic Right Ventricular Cardiomyopathy Registry, led by researcher Katia Chiampas. Sustained aerobic effort, not the genetic mutation alone, appears to move some carriers of the condition measurably closer to a life-threatening heart rhythm.
Arrhythmogenic cardiomyopathy, often shortened to ACM or called ARVC for its right-ventricular subtype, is a heritable condition that thins and scars heart muscle over time and substantially raises the risk of sudden cardiac death. People with the diagnosis, or a pathogenic gene variant linked to it, have long been steered away from high-intensity aerobic exercise, but the registry data is among the first to test that guidance against a group trained specifically for strength rather than treating all exercise as one category.
What Arrhythmogenic Cardiomyopathy Does to the Heart
Investigators defined a ventricular arrhythmia broadly for the purposes of the study: sustained ventricular tachycardia lasting more than 30 seconds at 100 beats per minute or faster, ventricular fibrillation or flutter, sudden cardiac arrest or death, or the use of an implantable cardiac device. Measured against that definition, endurance athletes were 58% more likely to experience one than participants in the sedentary or strength groups combined.
Across the full registry, 55% of participants experienced a ventricular arrhythmia at some point during the study period, and roughly half of those events happened around the time of enrollment, often following a diagnosis or a cardiac event that had already occurred. That pattern shows how much of the disease’s danger surfaces early, before years of tracked activity data can even accumulate.
How Endurance Training Compared With Strength and Sedentary Groups
Researchers sorted participants’ self-reported activity, gathered through phone interviews covering the years since childhood, into four categories: endurance athletes logged at least four hours of weekly vigorous aerobic activity such as running, cycling or swimming; strength athletes logged at least two hours of weekly weight training, climbing or martial arts; dual athletes met both thresholds; and sedentary participants met neither. Dual athletes, who trained in both disciplines, carried no additional risk beyond what endurance athletes alone showed, according to the retrospective review published in AJMC — meaning adding strength work on top of endurance training did not measurably change the aerobic-driven risk.
Self-reported activity also declined over time within the registry: aerobic exercise averaged about six hours a week before participants enrolled, dropping to roughly two hours a week within a few years afterward, while strength training fell from more than 2.75 hours weekly to under an hour. Most participants, 55%, fell into the dual-athlete category, followed by sedentary at 26%, endurance at 12% and strength at just 7%.
A 2013 Study Behind Today’s Exercise Guidelines
Current guidelines already restrict high-intensity aerobic exercise and competitive sports for people with ACM or a pathogenic desmosomal gene variant, guidance rooted partly in a 2013 Johns Hopkins study that found high-intensity exercise was associated with earlier disease onset and greater arrhythmic risk among carriers of ACM-linked mutations. That earlier work focused on aerobic intensity specifically, leaving open how strength-based training might fit into the same risk picture.
The new registry analysis extends that 2013 finding rather than overturning it: the 58% elevated risk sits squarely within the aerobic side of exercise the earlier study had already flagged, reinforcing more than a decade of guidance directed at endurance sports in particular, even as it clarifies where strength training falls outside that specific warning.
Who Was in the Johns Hopkins Registry
Participants in the study published in JACC: Clinical Electrophysiology were all adults in the United States, with a median age of 34 when they joined the registry and 44 by the time the study concluded. About 70% had received a formal ACM diagnosis, and the group was split almost evenly between men and women, drawn from phone interviews that traced activity levels back to age 10.
Cynthia James, research director of the Johns Hopkins ARVC Program and Center for Inherited Heart Diseases, said the registry’s value lies in what it lets doctors and patients do with the numbers. Physical activity matters enormously to people living with or at risk for the condition, James said in a statement, and findings like this one help support shared decisions between physicians and patients rather than a single blanket rule for everyone carrying the diagnosis.
Chiampas and her co-authors drew that distinction directly from the registry’s own numbers rather than from prior assumptions about what counts as safe exertion. A carrier who logs several hours of running or cycling a week is working with a materially different risk profile than one who lifts weights for the same amount of time, and the 58% gap between those two patterns is now measured rather than inferred.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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