Marius Myrstad, MD, PhD, FESC, is senior consultant and researcher at Baerum Hospital, Norway. Leader of the Norwegian Exercise and Atrial Fibrillation Initative NEXAF and principal investigator (PI) of the international randomized controlled trial (RCT) Effects of Detraining in Endurance Athletes with Atrial Fibrillation (NEXAF Detraining). Local PI of The Norwegian Exercise and Atrial Fibrillation Trial, a RCT on exercise in patients with atrial fibrillation. He is part of the Norwegian Atrial Fibrillation Research Network afib.no. Has published several papers based on clinical and epidemiological studies on atrial fibrillation in endurance athletes and in relation to exercise. Myrstad is a specialist in Geriatric Medicine and has been involved in the Birkebeiner Studies on aged athletes for more than a decade. Myrstad is also involved in research projects on frailty and delirium in geriatric patients with and without cardiovascular diseases. Passionate XC-skier and runner.