Can intense endurance exercise cause myocardial damage and fibrosis?

There has been long-standing debate as to whether intense endurance exercise provokes acute myocardial damage and whether cardiac remodeling associated with long-standing endurance training is entirely physiological. Despite the lack of concrete evidence on either side, the potential for serious clinical consequences, including life-threatening arrhythmias, elevates the importance of the debate. Studies have taught us that elite athletes enjoy excellent health, and athletic animal models consistently show up-regulation of molecular pathways, which are free of fibrosis and entirely different from those induced through pathological cardiac loading. On the other hand, extreme exercise has been associated with biochemical and functional evidence of acute damage, and some recent imaging techniques raise the possibility of small areas of myocardial scar. Moreover, some arrhythmias appear to be more prevalent amongst endurance athletes. Only large prospective trials will enable us to really assess the health benefits and risks of regular intense endurance sports.