VO2 max (also known as aerobic capacity) is the maximal amount of oxygen the body can consume during exercise. This is critical for endurance athletes because of the role oxygen plays in energy development. Specifically, the body uses oxygen to convert food into adenosine triphosphate (ATP), the human ‘gasoline’ needed to facilitate all muscular contraction and bodily processes. A central aspect of cycling performance is the ability to produce enough energy to complete workouts and competitive events at the highest level possible. More oxygen equates to greater ATP production, which means greater endurance on the bike. That’s why a high VO2 max is great for cyclists and other competitive endurance athletes. While it is not a very good predictor of cycling performance (lactate threshold is a better predictor, which is why we develop training zones based on LT instead of VO2 max), it is a very good predictor of endurance sports potential.
Aerobic capacity can only be measured in a lab setting using a cycling ergometer and a metabolic cart, which consists of several instruments that measure the volume of air the cyclist breathes, the amount of oxygen extracted from this air and amount of carbon dioxide produced. The test consists of pedaling at progressively higher workloads (typically increased every one to three minutes until the cyclist reaches his/her limit) while expired air is collected through a mouthpiece for analysis by the metabolic cart. A computer then calculates VO2 max, which can be articulated in both absolute and relative measures. The absolute measure is liters of oxygen utilized per minute (L/min). The relative measure, which is the more common usage, is milliliters of oxygen utilized per kilogram of body weight per minute (ml/kg/min). The average untrained person has a VO2 max of about 40 ml/kg/min, while well-trained cyclists typically have aerobic capacities in the range of 55 to 65 ml/kg/min. Of course, some élite athletes have much higher aerobic capacities. For example, Lance Armstrong’s VO2 max has been measured as high as 83 ml/kg/min.
If you want to have your aerobic capacity measured, you will need to find a local sports performance lab that provides metabolic testing. The number of labs is increasing and in some cases, it can be as simple as going to a local bike shop or university. Cyclists can often have lactate threshold and aerobic capacity measured at the same time. Just keep in mind that the tests can be a bit costly ($100 to $200 in many cases). Since lactate threshold is the more important measure for the development of training zones, and you can determine lactate threshold heart rate with a reasonable degree of accuracy in the field, you may justifiably decide to bypass aerobic capacity testing. However, if you decide to have it done, remember that aerobic capacity is not a great predictor of cycling performance, only potential. If your VO2 max is high, that does not guarantee you will be a great cyclist, although you are off to a nice start. On the other hand, if your aerobic capacity is relatively low, don’t be discouraged. With proper training and nutrition, you will still find great success in cycling!