| Summary: | Current knowledge about the relationship between exercise and cardiac remodelling is mostly based on studies of athletes. Little is known about cardiac adaptations to moderate doses of exercise in the general adult and elderly population, and whether exercise-induced cardiac remodelling is a benign physiological adaption of exercise or part of a pathophysiological mechanism. The main objective of this thesis was to study the association between physical activity (PA) and the structure and function of the left side of the heart. Also, we wanted to explore if exercise-related left atrial (LA) remodelling was associated with adverse cardiac alterations and increased risk of incident atrial fibrillation (AF). In paper I, we applied a longitudinal design with repeated measures of self-reported PA and echocardiographic structural and functional data. In paper II, we applied a cross-sectional design to investigate the association between device-based PA and LA size. In paper III, we applied a prospective design to investigate the association between self-reported PA, LA size, and risk of AF. The main findings of this thesis are that exercise-induced cardiac remodelling also occurs with moderate levels of habitual PA, and not only in endurance-trained athletes. Moreover, our results indicate that exercise-induced LA remodelling is a benign physiological adaptation to exercise, without being associated with reduced left ventricular (LV) diastolic function or increased risk of incident AF. Higher levels of PA were associated with increased LA size in general, and increased LV size in females. However, no change in pump function or atrioventricular ratio at rest was observed with higher levels of PA. Moreover, moderate levels of habitual PA were associated with reduced risk of AF, and active individuals with LA enlargement did not have higher risk of AF than either active or inactive with normal LA size. Nåværende kunnskap om sammenhengen mellom trening og hjerteremodellering er for det meste basert på studier av ...
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