What is VO2max
Filed under: Exercise Science
Maximum aerobic capacity, maximum oxygen consumption, or VO2Max, is a measure of the maximum volume of oxygen your body can process. It also provides a quantitative measure of a person's capacity for ATP (energy) resynthesis. VO2max is expressed in milliliters of oxygen per kilogram of body weight per minute or ml/kg/min.
VO2Max is primarily determined by genetics and is also connected to other physiologic factors such as heart size, stroke volume, blood hemoglobin levels, oxidative enzymes levels, mitochondria and capillary density, and muscle fiber type. Most of these factors are trainable to a certain degree.
These physiological factors that affect aerobic capacity are categorized into two areas: central and peripheral. The function of central factors is to deliver oxygen from the heart via the bloodstream to the working muscles. The main factor affecting delivery is cardiac output, or the amount of blood the heart can eject per minute. Cardiac output can be improved by progressive aerobic training, mainly by increasing the stroke volume, or the volume of blood the heart ejects per beat.
The main function of the peripheral factors is oxygen extraction from the blood as it reaches the working muscle. The most important peripheral factor is the arteriovenous oxygen difference (a-v O2 difference). This is the difference between the arterial oxygen content as it reaches the working muscle and the venous oxygen content as it leaves the working muscle. This difference in oxygen content provides us with an accurate account of oxygen extraction occurring in the working cells. Improvement in a-v O2 difference through aerobic training results because of increases in mitochondria and capillary density, increases in myoglobin and oxidative enzymes levels, and an increase in Type I slow twitch muscle fibers.
World-class male cyclists usually produce VO2Max numbers in the 70-80 ml/kg/min range and by comparison, normal, active male college students test in the 40-50 ml/kg/min range. Women usually test 10% lower in all categories. VO2Max will decline 1% per year after the age of 25. However, maintaining high intensity training will delay this decline until ages 35 or 40 and the reduction in VO2Max will be much slower than their sedentary counterpart.
VO2Max values can improve as much as 15%-20% in untrained individuals. Highly trained athletes can only expect to see a 3%-5% increase with specific, high intensity training. One of the best ways to increase your VO2Max is to train at, or near, your aerobic maximum. This high-intensity, interval type training is ideal for the strength and speed portion of your periodization schedule prior to the competitive stage. Intervals from 3-10 minutes at 106%-120% of 40K TT average power or 106% of 40K TT average HR repeated 4 to 6 times once or twice a week maximum.
TESTING
VO2Max testing can be measured in a lab directly or indirectly using field testing and estimating approximate values.
Direct measurement of VO2Max is determined by using an open circuit spirometer. In this method, the subject breathes through a special mask that collects and measures inspired and expired gases (O2 and CO2). The combined concentrations of these gases together with lung volume information are used to calculate VO2Max. To achieve these values, the subject performs continuous, progressive exercise on a treadmill or cycle ergometer until certain endpoint criteria are met.
Data from sub-maximal and/or indirect exercise tests can be used to predict VO2Max results. This is possible because heart rate and VO2 values are linear and follow the same progression. These indirect, sub-maximal tests can be done as field tests by using a simple 12-minute or 1.5 mile run. These tests are inexpensive and easy to perform, however, a certain amount of error is expected due to subject variability, and may vary from 10%-20%.