These substances leave the fiber by the same path as the oxygen enters. This excess energy is released as heat. This helps the body maintain its optimum operating temperature of 98.6 F. When available, the aerobic pathway always uses fatty acids. The muscles save glucose for the nervous system as often as possible. During rest, the aerobic pathway supplies the minimum need of limited muscle motion.
Strenuous exercise starts the two anaerobic pathways going.
Creatine phosphate and ATP are on opposite ends of a chemical spectrum. ATP releases energy and creatine phosphate gains it. This action takes place whether the cell has oxygen or not, because the reaction does not occur in the mitochondria. It happens within the muscle's protein filaments. During the short bursts of intensity demanded by power-strength creatine phosphate is both the first source of energy summoned and the first depleted.