VO2 max is considered to be the industry standard for measuring aerobic fitness.

V02 max is essentially your body's ability to extract oxygen from the blood and transport it to other tissues, namely the muscles. Utilisation of the new found oxygen is another factor in VO2 max.

Measured in millilitres of oxygen per kilogram of your weight per minute of aerobic exercise, abbreviated to ml/kg/min.

In general having a high VO2 max level will increase your performance at endurance events. Having an average VO2 Max level, however, does not mean you are unfit. Jonah Lomu of the New Zealand All Blacks has a relatively low VO2 Max level but he can run the 100m sprint in near record time. This is why Jonah is a world famous rugby player, not a cross-country skier.

On the note of cross-country skiing, the highest ever VO2 max level was that of a Scandinavian Cross-country skier with a level of 93 ml/kg/min. In contrast, the average American has a VO2 Max of 35 ml/kg/min. An elite marathon runner would normally have a VO2 Max of 70 ml/kg/min.

Your VO2 max can be measured in many different ways. The easiest method is to attempt the "bleep test" and calculate your level off of that. The most accurate method however, is to use a treadmill and several medical monitoring devices.

All VO2 Max figures from www.coolrunning.com