A simple explanation: Muscle tissue needs oxygen to function. The more the muscle is stressed, the more oxygen it needs. The maximum ability of muscle to 'consume' oxygen is called Vo2 Max. In other words, the more oxygen your muscle can consume, the harder it can and will work
Guys in the gym boast about the size of their 'dumb-bells', us cyclists boast about the size of our Vo2 max. ;D
Skinfold measurements are used to calculate your estimated body fat
Where a-v02 is the difference in oxygen concentration of blood leaving the heart (arterial) and returning to the heart (venous). This represents the volume of oxygen removed from the blood by the muscles during aerobic metabolism.
Q represents the cardiac output, or the amount of blood that that the heart can expell.
Both values are normaly measured per minute. VO2 is normaly measured indirectly at the mouth and here it is calculated using the difference in concentration of oxygen of inhaled and exhaled air x by the volume of exhaled air.
VO2 represents the rate of aerobic metabolism, during maximal exercise a plateux is acheived in VO2 and this maximum value is termed VO2 max. VO2 max therefore represents the maximal rate of aerobic metabolism and maximum capacity for aerobic work during exercise. As a result VO2 max is an important physiological measure for endurance performance.
Training for endurance cycling events should contain some training that directly stresses factors that affect Q and a-v02 difference. By overloading these factors you will cause adaptation and as long as all other factors remain consistant your VO2 max will increase.
You really need a coach if you wish to train for any cycling event as training needs to be individual (i.e. no programes from books), specific to the event, periodized, etc. The undertaking to plan this kind of appropriate training is often too much for a rider alone; lack of knowledge on training can result in gaps in performance, inability to listen to your own feedback often results in over/under training, every athlete needs to be geered up every now and again, etc.