What is VO2 MAX and how is a measurement taken? By how much can VO2 MAX be increased in the average person?
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:
For even more detail, including the associated math, see Wikipedia: V02 Max.
One note about VO2 max, is that it is becoming more and more an academic interest number, as studies are increasingly showing that it is a poor predictor of actual performance. The two numbers that are becoming more important/relevant are vVO2max, and tlimvVO2max.
vVO2max is the minimum running/cycling speed at which your VO2 max level is attained, and after a few minutes of which, additional power has to come from anaerobic sources. This number is receiving increased attention (especially in running) as economy of motion is becoming a factor. A more efficient athlete will be traveling faster when they hit VO2max, so their vVO2max is higher than a less efficient athlete. In cycling (especially for TT), aerodynamics and proper fit will increase economy (Getting more speed out of the same effort). In aerodynamics I include losing weight, as a larger person presents a larger wind profile, efficiency would be enhanced through a proper fit, and comfort/familiarity on your bike.
tlimvVO2max is simply the time limiter for VO2 max, or how long you can continue to keep your pace once you've hit your VO2 max. If two cyclists both hit their VO2 max at 26mph, but cyclist A has a tlim of 10 minutes, while cyclist B has a tlim of 15 minutes, cyclist B will win. (Assuming the finish line isn't 10 minutes away :p)
Both tlimv and vVO2 can be increased through greater efficiency and training, while VO2 is a relatively static number, and really only indicates potential, so while VO2max is an interesting number to know, simply knowing it won't really help you change anything in your training.
Vo2 Max is a measure of 2 things:
The combination of the 2 gives you your oxygen consumption rate, which is also known as Vo2 Max.