I was a competitive runner and cyclist most of my adult life, and did develop AF near the tail end of a 10km maintenance run eight years ago. In fact, I had two short runs of tachycardia/maybe SVT during cycling years prior to that, each lasting maybe five minutes. However, despite my own history, associated as it is, it was undiagnosed sleep apnea that set me off. Or, so the story goes... I wonder how many athletes actually have undiagnosed sleep apnea.