The project is an epidemiological PhD study based on data from the HUNT study, the Tromsø study, and the Birkebeiner study. The purpose of the study is to investigate the relationships between atrial fibrillation and physical activity, as well as the effects of physical activity on stroke and mortality in individuals with atrial fibrillation. This study is part of the Norwegian Exercise and Atrial Fibrillation Initiative (NEXAF), which aims to increase knowledge about atrial fibrillation and exercise.