On the Cellular Basis of Aerobic Fitness: Intensity-Dependence and Time-Course of Cardiomyocyte and Endothelial Adaptations to Exercise Training

Abstract

Beneficial effects of exercise are closely associated with fitness and maximal oxygen uptake (VO2max). Capacity for oxygen transport increases mainly by improved cardiac function, including larger chamber volumes, myocardial hypertrophy, and enhanced diastolic and systolic function. Higher arterial conductance, capillarity, and oxygen utilization in skeletal muscle also contribute. The present thesis investigates the cellular basis for cardiac and arterial effects; how they correlate with changes in VO2max during exercise training at high or moderate intensity, and during detraining.

The studies show that:

1. Regular aerobic exercise training increases running performance and VO2max, induces cardiac hypertrophy, and improves cardiomyocyte contractility and arterial endothelial function.

2. High intensity exercise is more effective than moderate intensity exercise to increase aerobic fitness.

3. VO2max correlates closely with cardiomyocytes size, contractility, and calcium handling during adaptation in the first weeks of exercise, during detraining, and with different training intensities.

We conclude that:

1. Aerobic fitness is intimately related to cardiomyocyte size and function.

2. The magnitude of adaptation to training depends on exercise intensity.

3. Intensity emerges as an important determinant for beneficial effects of exercise training.