Metabolic Transitions and Muscle Metabolic Stability: Effects of Exercise Training

In this chapter we present the mechanisms underlying oxygen uptake kinetics in humans. We provide evidence that the time constant of the primary component of the VYO2 on-kinetics and the magnitude of the slow component can be considered as indirect markers of the muscle metabolic stability during exercise. Good muscle metabolic stability means small decreases in muscle PCr concentration and ΔGATP, and minimal increases in muscle ADPfree, Pi, H+, IMP, AMP, and NH3 concentrations during exercise of a given power output (~ATP turnover). Furthermore, we propose mechanisms by which physical training: (1) enhances muscle metabolic stability; (2) accelerates the primary VYO2 on-kinetics; and (3) attenuates the slow component of VYO2 on-kinetics. Finally, we discuss the importance of the training-induced enhancement of muscle metabolic stability for improvement of muscle mechanical efficiency and exercise tolerance.