Exercise is good for you in all kinds of ways, there is no medicine like it to prevent a whole range of illnesses. But for some endurance athletes, exercise also comes with increased risk of a heart condition called atrial fibrillation. We look for the right way to think about the risks around exercise. Reporter: Paul Connolly Series Producer: Tom Colls Sound Engineer: Graham Puddifoot Editor: Richard Vadon (Picture: A cyclist training in the mountains Credit: anton5146/Getty Creative)