Aerobic capacity' (VO2 max)' describes the functional status of the cardiorespiratory system, (the heart, lungs and blood vessels). Aerobic capacity is defined as the maximum volume of oxygen that can be consumed by one's muscles during exercise. It is a function both of one's cardiorespiratory performance and of the ability of the muscles to extract the oxygen and fuel delivered to them. To measure maximal aerobic capacity, an exercise physiologist or physician typically directs a subject to exercise on a treadmill, first by walking at an easy pace and then, at set time intervals during graded exercise tests, gradually increasing the workload. The higher a cardiorespiratory endurance level, the more oxygen transported to exercising muscles and the longer exercise can be maintained without exhaustion. The higher aerobic capacity, the higher the level of aerobic fitness.
Right off of wikepedia, seems as though it's not that complicated, it involves both capacities.
