VO2max is the total amount of oxygen your body can consume in a minute. It can be expressed either as a total volume per minute (i.e. "absolute VO2max", typically 3 to 5 litres/min, but in some cases up to as much as 7.5 litres/min in the case of elite rowers), or as a volume per minute per kilogram of body weight ("relative VO2max", typically 35 to 50ml/min/kg, although the highest recorded figure in a human is just over 90ml/min/kg).
Before we get too impressed with ourselves as a species, it is worth noting that it has been reported that race horses can achieve 180ml/min/kg, huskies can clock in at 240ml/kg and apparently one prong-horned antelope managed 300ml/kg (we can't quite work out how they got it on the erg, but obviously someone managed it).
Runners always seem to be talking about their relative VO2max figures, whereas rowers prefer to talk about their absolute figures. Is this just habit or trend, or is there a reason for this?
As it happens, there is a reason. The amount of oxygen it takes to move a runner at a given speed is directly proportional to the weight of the runner (on the flat). Double the weight of the runner and you double the oxygen bill. For that reason, the relevant VO2max figure for the runner is per kilogram of body weight, i.e. relative VO2max.
So why don't rowers do the same thing? One has to start out on the water - the short answer is because we float. If you double the weight of the rower sitting in his boat, you do not
need to double the power output to go at the same speed, you need to increase it by 2 to the power of 2/9 (depending fractionally on boat class). If you increase the weight of the rower by 8%, then the power needed would be 1.08 to the power of 2/9.
On this basis the rower ought to be interested in hybrid of relative and absolute VO2max figures, namely VO2/(weight ^ 2/9)... but apparently that is considered excessively complicated. Absolute is close than relative for the water rower, so absolute it is.
Since we are on the topic, there are two interesting additional facts which are worth throwing into the article: VO2 scaling, and the size of rowers compared to runners.