Atrial fibrillation (AF) is the most frequent sustained arrhythmia and a common cause for stroke and heart failure (21). Increasing physical activity has convincingly shown to reduce the risk of AF in the general population (28). However, a growing body of literature supports a U-shaped relation between lifetime-accumulated high-intensity endurance training and AF in middle-aged men (1). The pathophysiology underlying this relation is incompletely understood with multiple hypothesized mechanisms, which probably in combination create the necessary substrate and trigger for AF onset. Initiating management of AF requires documentation of an AF episode, which can be challenging in athletes as it usually occurs intermittent. New wearable devices hold promise to facilitate early documentation and follow-up, but their reliability still