There is a selection problem isn't there? It all comes from the term "participating". Of course, those who do not participate will have a higher risk of cardiac arrest. Those capable of participating would have a lower risk. And, those who do not participate in marathons do many forms of exercise, including couch surfing. I see no point to the study. Why read a study that is flawed from the beginning.
But, the long-training marathoners will have a higher risk of damage in other tissues and in the ventricles of the heart. Moreover, the hardest trainers have shorter telomeres.
