Aerobic metabolism is the mainstay of energy provision in endurance exercise. Training adaptations are induced in the muscles actively used in the exercise; these adaptations are sustained by continued activity and lost following inactivity. In this article, the mechanisms of the muscle adaptations to the aerobic metabolism during the endurance exercise are analyzed through the muscle fiber type, the mitochondrial content, the capillarity density and the blood flow capacity, also the outside influences on the physiological process from the training intensity and duration are described.