Does too much exercise damage the heart? A narrative review of the long-term cardiovascular effects of intense training

: Long-term exposure to high-intensity endurance exercise induces significant physiological cardiovascular remodelling. However, recent evidence suggests that prolonged exercise in athletes, particularly those exposed to decades of intensive training, may be associated with features of cardiovascular "wear and tear". These include electrical changes such as an increased risk of sinus node dysfunction and atrial fibrillation as well as structural abnormalities such as focal non-ischemic fibrosis and coronary artery calcification, more frequently observed in middle-aged and older endurance athletes. These observations support that long-term high-intensity exercise may have deleterious cardiovascular effects in susceptible individuals, although the available data are primarily derived from male Caucasian athletes. While the clinical significance of these potentially maladaptive changes at the individual level remains uncertain, at a population level high intensities and volumes of physical activity are consistently associated with reduced cardiovascular and all-cause mortality compared with sedentary behaviour, although the incremental survival benefit may plateau at very high exercise volumes. This review critically appraises the available evidence on chronic adverse cardiovascular adaptations associated with intense endurance exercise, highlighting unresolved controversies, sex- and ethnicity-related knowledge gaps, and the need to balance potential risks against the well-established survival benefits of lifelong physical activity.