I often receive telephone calls from runners wanting to know if it would be possible to measure their VO2 max. My standard answer is something along the lines that it is, indeed, possible. However, I then go on to ask why they want to have their VO2 max measured? There is usually one of two replies. Firstly, I am told, by knowing his or her VO2 max the runner will know that esoteric time that he or she is ultimately capable of running for some particular race distance, and therefore their ultimate potential as a runner. Secondly, once their VO2 max is known it will be possible to prescribe the ultimate personalised training schedule. My response to both is that knowing the VO2 max of a runner does not answer either question.
It is widely believed that the VO2 max is genetically determined and unchanging and that an individual is born with either a high or low "max". Someone with a high value has muscles that are capable of utilising large amounts of oxygen and a cardiovascular system capable of delivering this volume of oxygen. The athlete is able to run at a maximum aerobic speed that this oxygen supply can sustain. In this paradigm it does not appear to matter whether the runner is unfit or superbly fit, the outcome of a VO2 max test remains the same. However, it is intuitively obvious that when fit the athlete can run much faster on the treadmill than when unfit. Thus, since VO2 max is genetically determined and does not change (in this model), VO2 max would be reached at a relatively slow running speed when a runner is unfit compared to when very fit, when a much higher speed can be reached on the treadmill. This means that in a totally unfit world-class runner we would measure a high VO2 max (say 75 ml/kg/min or higher) at a speed of maybe 17 km/hr on the treadmill. When very fit the same athlete will reach the same VO2 max at a speed of about 24 km/hr. The problem is that such a high VO2 max is never measured at a speed of just 17 km/hr. This would be almost impossibly inefficient. The theory of a genetically set and unchanging VO2 max therefore begins to appear a little shaky.
