Atrial fibrillation is primarily a problem of older age and the risk factors for atrial fibrillation in older age are well described: older age, male sex, valve disease, heart failure, systolic blood pressure and Body Mass Index.1 But a significant minority of atrial fibrillation presents in younger patients without obvious morbidities or risk factors: lone atrial fibrillation. This may have a more benign prognosis to atrial fibrillation in older adults.2

A persistent puzzle about the causes of lone atrial fibrillation has been the relationship between physical activity and the onset of lone atrial fibrillation. Could being more physically active also have adverse consequences?

Plausible mechanisms have been advanced for an increased risk of atrial fibrillation in endurance athletes: increased left …