The oxygen uptake (VO2) of an athlete is the amount of oxygen which the body uses in a minute. It should not be confused with the ventilation rate, which is the total amount of air per minute passing in and out of the lungs. Oxygen uptake is believed to be one of the best indicators of an athlete's overall fitness. Most training works to improve the athlete's ability to move oxygen into the cells and improve the ability of the cells to use the oxygen.
The most significant improvements in response to aerobic training are in oxygen uptake (VO2). The body consumes only small amounts of oxygen at rest. However, as we begin to exercise, the mitochondria in the cells use more oxygen in the provision of energy. Maximal oxygen uptake, or VO2 max, is regarded as the best indicator of cardiorespiratory endurance because it indicates the maximal amount of oxygen that muscles can absorb and use at that level of work.
Maximal oxygen uptake is relatively easy to estimate using tests such as bicycle ergometry in the laboratory, or field tests such as the 12-minute run or the multistage fitness test. A high VO2 max indicates a superior oxygen
delivery system and contributes to outstanding endurance performance. Most tests that measure VO2 max are able to take account of individual differences. Measurements are expressed in millilitres of oxygen per kilogram of body weight per minute (mL/kg/min). Average VO2 max values are about 45 mL/kg/min for 17-year-old boys and 40 mL/kg/min for girls. The lower value for girls reflects the fact that females have less muscle tissue as a percentage of total body weight (less lean body mass) than males and less oxygen-carrying capacity due to lower
haemoglobin levels. Oxygen uptake decreases at the rate of about one per cent per year after the age of 25, but is influenced greatly by aerobic training. Training appreciably increases VO2 max even in an eight- to 12-week period. A 15–20 per cent increase is typical for the average inactive person who applies the FITT formula for a six-month period. This reflects an improvement of 35 to 42 mL/kg/min. The highest recorded value for a female, world-class, endurance athlete is 75 mL/ kg/min and the highest for a male athlete is 94 mL/kg/min.