Train to the VO2 max

The V stands for 'volume' while O2 is the chemical notation for oxygen. VO2 max, also known as 'maximal oxygen uptake' can be expressed in many ways (from liters of oxygen per minute or the more normalized milliliters of oxygen per kilogram of bodyweight per minute). It is a way to not only compare the performance of endurance athletes, but is also a relative indicator of overall fitness.

Oxygen consumption has a direct link to energy expenditure. Therefore, maximum oxygen uptake is a direct measurement of aerobic capacity. It can not only help determine just how much exercise you can perform in a given amount of time, but also predict the number of calories you will burn. Understanding of VO2 max really begins within the muscle. At rest, muscles expend relatively little energy. When contracting, muscles create a high demand for energy. The body processes oxygen and releases carbon dioxide (CO2) as the result. Measuring the amount of carbon dioxide exhaled is one way to infer VO2 max.

The process of using oxygen for energy requires two key components: delivery and utilization. Delivery is achieved through breathing (the respiratory system) and circulation (the cardiovascular system). This is one reason why exercising improves cardiovascular health: in order to become more efficient at exercise, the body must become more effective at delivering oxygen. This is achieved through improvements to the cardiovascular system. Training improves your stroke volume, or the amount of blood your heart can pump in one contraction. Increasing stroke volume improves delivery and therefore will increase your VO2 max.

Stroke volume, however, is not the only factor. The other component is utilization. The muscle must effectively process the oxygen for energy. This is related to mitochondria and myoglobin in the muscles. Mitochondria is known as the 'cellular power plant' and generates the ATP molecule that is the 'chemical fuel' for cells. Myoglobin carries oxygen within the muscle. It uses an iron atom that bonds to the oxygen atom. This bond creates the pigment that causes meat to turn red or pink (heating breaks this bond, which is why 'well done' or cooked meat turns brown). Both mitochondria and myoglobin work together to improve the ability of the muscle to utilize oxygen for energy.

Studies show that while exercise can increase the muscle's ability to utilize oxygen several times over, it only has a minor (10 - 20 percent) impact on cardiovascular output. Therefore, the delivery system is the limiting factor in increasing your VO2 max. Your heart simply cannot keep up with your muscle's demands and becomes the bottleneck for delivering oxygen to the cells that need it.

VO2 max is measured several ways. The most common is the treadmill test. Usually, the treadmill is started with no incline and a slow speed. Then, after a predetermined interval of a few seconds to several minutes, either the incline, the speed, or both are slowly increased. This continues until you can no longer maintain the pace. Your time on the treadmill can be used to calculate your VO2 max. You may also be hooked up a respirator that measures oxygen and carbon dioxide intake and exhalation. Because of the way VO2max is related to training and energy expenditure, you can also estimate it based on simple training runs.

The formula to compute your VO2max from a race is:

(-4.60 + 0.182258 * velocity in meters per minute + 0.000104 * velocity in meters per minute squared) /
(0.8 + 0.1894393 * e ^ (-0.012778 * time in minutes) + 0.2989558 * e ^ (-0.1932605 * time in minutes))

A poor VO2 max for females is typically anything less than 20 while for males is anything less than 30 (ml/kg/min). Superior VO2max scores are anything over 40 (females) and over 50 (males). To compare this with elite athletes, top cyclist Lance Armstrong was computed to have a VO2 max of 84, while marathon-running legend Frank Shorter is believed to have a VO2 max of 71.

VO2 max can be used to estimate the calories you burn during an activity. The first step is to estimate your maximum heart rate (MHR). The simplest method is to take 220 - your age in years. Therefore, a 35-year-old would have an MHR of 185. During exercise, your percentage of MHR determines both the percentage of VO2 max you are training at as well as average calories burned per minute:



As you can see, more intense exercise will burn more calories per minute. Doubling the effort (based on your heart rate) more than quadruples the energy output.

There is no single measure of overall fitness. The VO2 max, however, can give you a good idea of your relative level of cardiovascular fitness and how well you have improved with time. By learning your VO2 max, you can plot your progress and better understand your body's response to training. Improving this key parameter will also enable you perform cardio more intensely and for longer periods of time. If you are looking to burn calories, understanding your VO2 max can help you maximize calorie burn during your training sessions. The next time you perform an endurance event or training session, be sure to take your workout to the VO2 max.