Dynamics of exercise training and detraining induced cardiac adaptations

The effect of regular physical activity has been provided by numerous investigations in cardiology: both its role in primary and secondary cardiovascular prevention, as well as exercise-induced cardiac hypertrophy in athletes have already been well characterized. In this short review, we would summarize the rate of development and regression of the cardiac adaptations induced by long-term, regular training and its cessation. While most of the cross-sectional studies in sports cardiology compared athletes to healthy controls, we investigated longitudinal follow-up studies, those also have baseline data before regular exercise and/or detraining period. Intense exercise training induces significant improvement in functional characteristics after approximately two weeks, while the first marked alterations in sinus bradycardia and left ventricular (LV) hypertrophy have been observed after two months of regular physical activity. Similar tendency with some earlier reports of morphological alterations has been observed in small animal studies. Both human and experimental data imply rapid morphological, functional, and electrical regression after cessation of exercise stimulus. These information suggest that exercise-associated cardiac functional improvements (early diastolic filling, maximal oxygen uptake) of the heart manifests earlier than the morphological and electrical alterations. The increased functional properties might be the primer alteration while the morphological and electrical adaptation might be a secondary consequence of the regular hemodynamic overload of the heart and systemic circulation. The regression of exercise-induced alterations seems to be an accelerated process compared to its development.