Oxygen Transport in Humans: Physiological and Environmental Modulation

This doctoral thesis examined how oxygen transport in humans is modulated by physiological determinants and environmental interventions across multiple domains of exercise physiology. Specifically, it investigated whether intermittent hypoxic training improves maximal oxygen uptake and performance beyond normoxic training, which biological factors determine cycling efficiency at different exercise intensities, whether aging alters the relative contribution of oxygen delivery and extraction to oxygen uptake kinetics during small-muscle-mass exercise, and whether hyperoxic training induces superior aerobic and muscular adaptations. The findings showed that intermittent hypoxic training does not provide clear benefits over normoxic training for maximal oxygen uptake or performance, and that hyperoxic training does not enhance maximal oxygen uptake despite producing locomotor-specific performance gains. In addition, cycling efficiency was associated with skeletal muscle oxidative phosphorylation capacity and fiber cross-sectional area, while aging impaired oxygen uptake kinetics during high-intensity exercise primarily through limitations in oxygen delivery. Overall, the thesis showed that oxygen transport in humans is determined by the interaction between central and peripheral physiological factors, with environmental manipulations exerting context-dependent rather than universally beneficial effects.