For years scientists, coaches, and athletes have believed there were only three variables that can be improved to increase fitness. They are:
Lactate threshold (LT): A scientist would say something such as, This is the onset of blood lactate accumulation, or the intensity of exercise at which the production of lactate equals its clearance. Most riders say they are just starting to 'redline' when they pass through this high level of intensity. On a 1 to 10 scale of exertion, LT is about 7 or 8.
Economy: This is generally determined as the percentage of the VO2max sustained at a particular submaximal intensity. For example, in riding, economy could be defined as the quantity of oxygen consumed per minute and per kg of body weight at a given sub maximal velocity. It's just like a fuel rating for your car - how much oxygen does it take you to go one mile.
VO2max: Also known as 'aerobic capacity,' this is the maximum amount of oxygen, in milliliters, one can use in one minute of all-out exercise per kilogram of body weight. VO2max is largely determined by genetics.
But now Veronique Billat's research shows that there are two, unique aspects of VO2max that have been overlooked and are just as important as the above. They are:
vVO2max is the velocity, or power output on a bike, which produces VO2max, in other words, causes your body to utilize oxygen at its highest possible rate.
tlimVO2max is the amount of time you can exercise at vVO2max before you fatigue and have to slow down.