The importance of oxygen extraction and blood volume for maximal oxygen uptake

During whole body exercise, the metabolic capacity of the exercising muscles is in excess of oxygen delivery. Despite this, endurance training by use of cycling and running increases the mitochondrial volume and capillary density in the activated muscles. These adaptations have been suggested to be important for the endurance more than VO2max However, the metabolic capacity of the muscles can be fully exhausted during maximal exercise with a smaller muscle mass, for instance in one-legged knee-extension. Moreover, it has also been shown that the ratio between one-legged knee-extension VO2max and whole body VO2max is the same in endurance trained and untrained individuals. Despite extensive research during the last decades, we do not fully understand the significance of the large metabolic reserve in the muscles.