Veteran male athletes who have spent years training at high intensity may be at greater risk of serious heart problems while exercising, new University of Leeds research shows. The study shows that male endurance athletes aged over 50 may be more likely to experience abnormal heart rhythms during training if they already have scarring in their heart. The team says their research shows that exercise itself is not dangerous - but the findings suggest that the presence of scar tissue in the heart increases the risk of potentially dangerous heart problems during physical activity.