VO2 max

VO2 max is a measure of the greatest amount of oxygen a person consumes when exercising at a high rate of intensity. Testing a person's VO₂ max level is considered the best way to measure the health and exercise capacity of the person's cardiovascular system. The test is sometimes called a cardiorespiratory fitness (CRF) test. It is also a good way to measure a person's ability to do aerobic exercise. The test is accomplished with special equipment that captures and measures how much air the person breathes in and out during exercise.

Background

Measuring the maximum volume of oxygen (VO2 max) that a person uses when exercising as hard as possible is important as a measure of fitness. It also measures cardiovascular health. During exercise, the cardiovascular system—the heart and the arteries, veins, and other vessels that circulate blood into the lungs and throughout the body—are put to the test.

Aerobic exercises such as walking and running require oxygen to help the body burn the fuel needed to generate movement. This requires the heart to pump more blood through the lungs and into the blood vessels to be carried throughout the body. The oxygen helps the body generate energy to power the muscles. The harder a person exercises, for example, sprinting or bicycling at a high speed, the more energy is needed and the more oxygen the person uses to make that energy.

The health and condition of the systems of the human body, including the cardiovascular and respiratory systems, can be affected by a number of elements. The body's overall health and the amount and intensity of the exercise a person gets are key factors. In general, the more a person exercises at a higher intensity, the more efficiently that person's cardiovascular and respiratory systems will function. Therefore, VO₂ max is an important measure of a person's overall health.

Overview

The person completing a VO₂ max test will generally use a treadmill to exercise while he or she is attached to monitoring equipment. The equipment includes a specially designed mask that delivers specific amounts of air, and captures and measures the air the person breathes out. The mask makes it possible for testers to tell exactly what gases are in the air the person inhales and exhales. As a result, the testers know exactly how much oxygen the person is using. This result—the VO₂ max—is reported as milliliters of oxygen used per minute per kilogram of body weight. The testers will generally also be able to determine the person's resting heart rate and the heart rate during exercise.

After being fitted to the mask, the person will usually step onto a treadmill and begin exercising. The intensity of the exercise will be amplified every few minutes by increasing the treadmill's speed and incline. Careful readings will be made of the person's oxygen usage as the test continues.

The intensity and length of the test depend on what the testers are attempting to determine. For a non-athlete where a baseline of the health of the cardiovascular system and overall fitness are desired, the person may not exercise or use the breathing apparatus. The testers will use heart rate and the person's own estimation of the amount and intensity of their exercise to help determine the VO₂ rate. In other cases, the person will exercise lightly, walking for the equivalent of about a mile on the treadmill. The person's heart rate and how well his or her system responded to the exercise will be used to estimate a VO₂ level. A person may also use the treadmill and exercise to exhaustion; the testers will use the highest speed and the distance and time he or she was able to exercise to determine the VO₂ level. Finally, the person can use the full breathing apparatus and treadmill, and exercise to exhaustion to determine the amount of oxygen used. This is the most accurate way to determine a VO₂ level and is usually used with athletes who want to measure and/or improve their cardiorespiratory fitness.

This is the primary way to measure VO₂ max levels. For many years, it was mostly athletes who were interested in knowing how efficiently their bodies used oxygen; exercising to exhaustion on the treadmill while measuring how much oxygen was used provided the most definitive answer to this. Additional ways came into use as physicians began to see the value of knowing a patient's VO₂ level in determining cardiorespiratory health in casual athletes and non-athletes.

It is believed that heredity is responsible for about 50 percent of a person's VO₂ max level. The remainder is determined by individual factors such as the type and amount of exercise a person gets. However, it is possible to improve a VO₂ level by improving the quality of exercise one does.

While VO₂ testing has long been used by athletes, it could become more commonplace. In 2016, the American Heart Association (AHA) issued a scientific statement that said VO₂ max levels should be considered as important as pulse, blood pressure, and other vital signs in determining a person's health. The AHA report indicated that VO₂ max levels were more accurate at predicting a person's likelihood of dying of certain diseases than high blood pressure or the amount of risk factors the person had. The AHA statement said that low VO₂ levels are associated with many potentially fatal conditions, including type 2 diabetes, dementia, Alzheimer's disease, depression, and heart disease.

The statement emphasized that exercise for exercise's sake is not necessarily enough. The exercise has to be the right type and intensity to improve the VO₂ level if it is truly to have an impact on a person's health. The highest mortality rates are seen in people whose levels are below eighteen milliliters of oxygen per kilogram per minute. Optimal rates are at thirty-five milliliters of oxygen per kilogram per minute. A physician can help determine a person's VO₂ max level or direct a patient for testing.

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