Simple plain English explanation of VO2 MAX
VO2 Max refers to the maximum volume of oxygen that an individual can use at maximum levels of intense aerobic exercise. It is usually reported as as milliliters of oxygen used in one minute per kilogram of body weight, though sometimes you see liters of oxygen per minute with no adjustment for body weight. The former measurement is more useful in exercise and sports science since it allows the measurement to be compared among athletes of widely different weights.

It is usually measured in a fitness lab setting using either an exercise bike or a treadmill. The test subject wears a mask and heart rate monitor. The mask is connected to a device that collects and measures of the volume and oxygen concentration of inhaled and exhaled air.

At some point below maximum effort the body switches from aerobic to anerobic processes to generate energy. Exercise intensity is increased gradually until the subject is at a maximum aerobic effort - beyond which there is not or only negligible increase in oxygen uptake. That is the VO2 Max point.

I don't know how much it can be increased in any individual, and there are both genetic and exercise components. This page lists that:


  The average for a sedentary individual is close to 35 ml/kg/min. Elite endurance athletes often average 70 ml/kg/min. One of the highest recorded VO2 max results (90 ml/kg/min) was that of a cross country skier. Cyclist Lance Armstrong's VO2 max was reported at 85 ml/kg/min.


For even more detail, including the associated math, see Wikipedia: V02 Max.