Expansion
Cardiac output is the main limiting factor, not the lungs
Expansion
VO2 max = maximal cardiac output x maximal arteriovenous oxygen difference
Typical values: about 35 to 45 ml/kg/min in untrained adults, over 80 in elite endurance athletes.
Limiting factors, in order of importance:
- Cardiac output, specifically maximal stroke volume: the principal limit in healthy people
- Oxygen carrying capacity (haemoglobin), which is why altitude training and, illicitly, blood doping raise it
- Muscle oxidative capacity and capillary density
- Pulmonary function, which is not limiting in most healthy people, since arterial saturation is maintained and substantial breathing reserve remains. Elite athletes are the exception, some developing exercise-induced arterial hypoxaemia
For performance, the lactate (anaerobic) threshold matters more than VO2 max itself, since it determines the fraction of maximum that can be sustained. Two athletes with the same VO2 max can differ greatly in endurance performance.
A plateau in oxygen uptake despite increasing workload is the defining criterion of a true maximal test.