Purpose: There is some evidence that physical training, especially endurance training, increases the risk of atrial fibrillation. But results are conflicting and studies have used widely different assessments of physical activity. We performed a systematic review aiming to investigate the association of exercise with risk of atrial fibrillation, taking into account the intensity and duration of training. Methods: We performed a systematic review of all studies investigating associations of exercise with risk of atrial fibrillation, using a predefined protocol. Because studies of total physical activity were scarce, we limited the analysis to studies reporting leisure-time activity. We quantified the exercise in the included studies as metabolic equivalent hours/week (METh/w). We thereafter used a network metaanalysis technique to summarize multivariable-adjusted risk estimates of atrial fibrillation across the different studies. Results: Ten (eight cohort and two case-control) studies including a total of 111,282 persons and 4,633 atrial fibrillation cases fulfilled our inclusion criteria and were used for all analyses. There was a trend towards higher risk of atrial fibrillation with higher weekly amount of exercise (p=0.04). Compared to persons who exercised 0-5 METh/w, those who exercised more than 100 METh/w had a more than five-fold higher risk of atrial fibrillation, with statistically non-significant risk elevations in intermediate exercise groups (Fig. 1). Conclusions: Higher weekly exercise amount was on average associated with higher risk of atrial fibrillation, across a variety of study samples and types. The risk increase was most notable for those with a very high exercise level. (Figure Presented).