ATP production, including factors that maximize this production process, has been the guiding theory in the study of endurance in the cellular level. Pioneers (Davies, 1981; Holloszy, 1967) have explored the biochemical effects of exercise to muscles and mitochondria, including the activity of respiratory enzymes during endurance training. It is directly presented how in these studies endurance training and mitochondrial development of an organism are related. Oxidative capacity was also found to be correlated with this endurance capability.