http://www.bodybuilding.com/fun/vo2max.htm
This is a calculator for establishing your VO2 Max based upon the distance that can be run in 12 minutes.
This makes it an ideal test to perform regularly in a Gym on a treadmill.
VO2 Max is related to the amount of oxygen that your body can process during aerobic exercise. The higher the value the fitter you are.
Developer Rants 