AF risk factors include obesity, diabetes, hypertension, inactivity, alcohol use, obstructive sleep apnea, and heart disease. Sustained weight loss (>10%) can prevent progression from paroxysmal (short episodes) to permanent AF. Thus it is not surprising that exercise can mitigate AF risk via weight reduction, blood pressure lowering, and improved glycemic control. In addition, exercise improves autonomic balance (increased parasympathetic/vagal tone ("rest and digest"), decreased sympathetic drive ("fight or flight)), lowers resting heart rate, and reduces inflammation/oxidative stress, which are all protective against AF. About 3.5 hours/week of moderate activity may lower AF risk by up to ~10%.
However, paradoxically, very high volumes and intensities of exercise (e.g. prolonged endurance training) are associated with higher risk of “lone AF,” especially in men. Lone AF refers to cases without structural heart disease or other obvious cause. The thought is that at extreme levels of exercise, the heart undergoes adaptations such as atrial remodeling (dilation) that potentially offsets benefits from exercise.
A recent editorial in the British Journal of Sports Medicine highlighted this apparent contradiction by noting that the "sweet spot" is moderate exercise in between complete inactivity and overly strenuous physical activity. They described a U-shaped dose response curve (Figure 1) with lowest AF risk at moderate volumes of exercise, and with potential risk increase at very high, long-term endurance doses.
The editorial cited Elosua et al. (2006) who asked whether long-term, high-dose endurance sport is associated with lone AF. These authors ran a case-control comparison of lone AF (LAF) cases versus controls without LAF. A total of 70 patients (51 men) younger than 65 years of age with lone LAF were identified from hospital records of 1160 consecutive patients seen at the outpatient arrhythmia clinic between October 1997 and March 1999. Two age-matched controls for each case were selected from the general population.
The proportion of patients with LAF who reported current sport practice (31%) was higher than that observed in controls (14%). The property of "current sport practice" was assessed based a questionnaire filled out by the subjects. To make this assessment more quantitative, the researchers defined high exercise exposure as >1,500 lifetime hours of sport practice -- a proxy for very high cumulative training load typical of sustained endurance participation. Spread out over say 10 years, >1500 lifetime hours of sport practices amounts to 150 hours per year or about 3 hours per week. This may not seem like intensive training, but the 10 year commitment is a marker for a serious endurance athlete.
Logistic regression controlled for possible confounders and resulted in an odds-ratio (OR) of 2.87 (CI: 1.20-6.91). In other words, people with LAF were roughly three times more likely to have accumulated greater than 1500 h of lifetime sport practice than those without LAF.
These data were consistent with a different study by Molina et al. (2008) that estimated an 8.8-fold higher risk of incident/lone AF in a cohort of marathon runners compared to sedentary peers. Interestingly, a larger left-atrial size was also found in the runners.
In terms of mechanism, structural remodeling of the atria is one possible pathway by which intensive chronic endurance training may increase the likelihood LAF. For example, excessive load on the heart may cause atrial dilation, fibrosis (excess extracellular matrix), repetitive atrial strain, and micro-injury.
On the other hand, more moderate exercise has demonstrated salutory effects on reducing AF risk. For example, a prospective cohort analysis of older adults (≥65 years) evaluated whether habitual physical activity predicts future AF. Participants achieving ~600 kcal/week of leisure-time activity showed a ~44% lower AF incidence versus less active peers. The ~600 kcal/week threshold corresponds to modest weekly exercise volumes (e.g., regular walking), and is somewhat less than the 150 minutes/week of moderate aerobic activity recommended by the CDC.
Interestingly, when the researchers examined exercise intensity (not volume as in previous paragraph), compared to no regular exercise, individuals with moderate-intensity exercise had 28% lower risk of AF than those with no regular exercise, but individuals with high-intensity exercise did not have significantly lower risk (13% lower) than the no regular exercise control. This resulted in a U-shaped dose-response curve once again supporting the notion that high intensity exercise is not as good for AF as moderate exercise in this broader subject population that was not athlete-focused.
Overall the clinical implications are that moderate, sustainable activity confers meaningful AF protection in older adults. Furthermore, adverse events during moderate, supervised programs are rare. One key is personalization that takes into account age, comorbidities, and exercise habits. From an AF perspective, one wants to adjust intensity and volume to stay within the moderate range. For high exercise dose athletes, it is important to discuss lifetime load, incorporate down-weeks, monitor symptoms such as atrial size, and evaluate palpitations promptly.
In summary, AF risk versus exercise follows a U-shaped pattern (Figure 1): lowest risk at moderate volumes, with potential risk increase at very high, long-term endurance doses. Moderate activity is linked to lower AF incidence and prevalence, while extreme endurance exposure (e.g. >1,500 lifetime hours) is associated with higher AF prevalence, especially in men.
Figure 1. The somewhat surprising U-shaped curve of AF to exercise dose. The dose-response curve is a schematic diagram but reflects data from studies including those described in the main text. Too little exercise carries risk from well-characterized factors such as hypertension, obesity, and diabetes. Too much strenuous (endurance) exercise may result in elevated risk for lone AF (LAF) especially in men. The sweet spot seems to be moderate exercise (reproduced from Marwaha and Sharma, British Journal of Sports Medicine, 2025).
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