BMJ Group Jun 10 2026 Changes to the heart linked to marathon running vary by age, sex, and training level, finds a synthesis of the available data, published in the open access journal  BMJ Open Sport & Exercise Medicine. But it's not clear if these changes represent normal physiological responses to endurance exercise or whether they are long term (mal)adaptations, the findings indicate. It's known that both low and extremely high levels of exercise may increase the risk of death, note the