The purpose of the VO2 Test is to gather physiological performance data during a graded exercise test. During this test, the body is subjected to gradually increasing exercise levels. The testing equipment measures the heart rate, pulmonary ventilation and gas exchange at each of the exercise levels. VO2 stands for volume of oxygen consumed; Values of Vo2 are reported in milliliters per minute. These values are often normalized to the weight of the person being measured. The VO2 is the then reported in milliliters per minute per kilogram of body weight. The maximum amount of oxygen than an individual can consume is referred to as their "VO2 max" and is the ultimate measure of their level of fitness. Factors that affect a person's VO2 max include level of cardiac and pulmonary fitness, muscle mass, muscle perfusion, etc. Exercise levels for a given individual are often determined as a percent of their maximum VO2. Another valuable piece of information that can be obtained from a VO2 test is the anaerobic or ventilatory threshold. The anaerobic threshold is the level of exercise beyond which lactic acid begins to accumulate in the muscles. As a person exercises, the muscles consume oxygen and produce carbon dioxide and lactic acid. As long as the heart and lungs provide enough blood flow and enough oxygen to the muscles, the muscles can operate "aerobically" (aerobic- meaning "with oxygen") in a relatively pain-free state for long periods of time. As the level of exertion increases, the muscles require more oxygen than the body can provide and the metabolism becomes "anaerobic" (anaerobic- meaning "without oxygen"). In anaerobic metabolism, lactic acid accumulates in the muscles and the muscles become fatigued. The anaerobic metabolism relies heavily on the glucose (sugar) as an energy source. Therefore, the ideal exertion level at which fat metabolism is maximized and fatigued and muscle soreness is minimized is a level just below the anaerobic threshold. The Metabolic Assessment also measures the heart rate observed during the exercise test. Heart rate is used then to give the user metabolic reference points that indicate their level of exertion. For example, if the Metabolic Assessment determines that an individual anaerobic threshold occurs at 22 milliliters of oxygen per kilogram per minute, and that the heart rate at that exertion level was 134 beats per minute, then that individual need only monitor the heart rate in the future to know when his or her exertion level had become anaerobic. Heart rate monitoring during a metabolic test defines the unique relationship between heart rate and calorie consumption for the tested individual. Using the Fitness Report that you receive, a tested individual will know how many calories are consumed for every exercise heart rate level.