Strength training safe for people with arrhythmogenic cardiomyopathy, Johns Hopkins study finds

People with arrhythmogenic cardiomyopathy live under a particular constraint: their hearts, shaped by genetic mutations that weaken the muscle's ability to contract and pump blood, cannot tolerate the stress of high-intensity aerobic exercise. A bout of sprinting or competitive cycling can damage those already-fragile cells, sometimes triggering sudden cardiac arrest or death—events that tend to strike people in their 20s and 40s. Doctors have long known to warn patients away from endurance sports. But they've had almost no data to guide decisions about strength training, which stresses the heart in a fundamentally different way. A new study from Johns Hopkins, published this week in JACC: Clinical Electrophysiology, suggests that weight lifting and similar resistance work may be safe for this population in ways that running and cycling are not.

Researchers at Johns Hopkins partnered with 355 people enrolled in the Arrhythmogenic Right Ventricular Cardiomyopathy Registry to trace their exercise habits from age 10 onward and compare those patterns to the cardiac events they experienced. The participants, a median age of 34 when they entered the study and 44 when it concluded, answered questions about their physical activity over the phone. The team sorted them into four groups: those who did endurance exercise (at least four hours weekly of vigorous aerobic activity like cycling, swimming, or running); those who did strength training (at least two hours weekly of weightlifting, climbing, or martial arts); those who did both; and those who were sedentary.

The results diverged sharply by exercise type. Endurance athletes were 58 percent more likely to experience a sustained ventricular arrhythmia—a rapid heartbeat lasting more than 30 seconds, or fibrillation, or cardiac arrest, or the need for an implantable device—compared to the sedentary group and the strength-training group. Strength athletes, by contrast, showed no increased risk compared to sedentary participants. People who did both endurance and strength work carried the same elevated risk as pure endurance athletes, suggesting that the aerobic component drove the danger.

About 55 percent of the study population experienced some form of ventricular arrhythmia during the follow-up period, though roughly half of those events occurred at or near the time of enrollment, often following a diagnosis or a cardiac event. The majority of participants—55 percent—were dual athletes, followed by sedentary individuals (26 percent), endurance athletes (12 percent), and strength athletes (7 percent). Seventy percent had a confirmed diagnosis of arrhythmic cardiomyopathy; the rest carried genetic risk.

The finding matters because exercise is not optional for most people. It shapes physical health, mental wellbeing, and quality of life. Blanket restrictions on all vigorous activity can be psychologically and medically costly. Lili Barouch, the senior author and director of the sports cardiology program at Johns Hopkins' Ciccarone Center for the Prevention of Cardiovascular Disease, framed the study as an opening toward more nuanced guidance. "There have been a lot of questions about the safety of strength training for people living with or at risk for arrhythmogenic cardiomyopathy," she said. "This study opens the door to help researchers further assess this—and supports continued shifts with moving away from blanket recommendations for exercise to support personalized decision-making between physicians and patients."

One in every 1,000 to 5,000 people worldwide carry an arrhythmogenic cardiomyopathy diagnosis. For them, the distinction between types of exercise is no longer theoretical. It is the difference between a life that includes the gym and one that does not. The study tracked a shift in behavior over time: participants averaged six hours of weekly aerobic exercise before joining the registry and about two hours a few years later. Strength training dropped from an average of 2.75 hours weekly to just under an hour. Whether those reductions reflected medical advice, aging, or changing interest is unclear. What is clear is that people with this condition are already modifying their activity. The Johns Hopkins findings suggest that at least some of that modification may be unnecessary—that strength work, unlike endurance work, does not appear to push the heart toward dangerous rhythms. The next step is for physicians and patients to use that information together to make decisions that fit individual lives.