VO2 Max (Peak Aerobic Capacity) Testing

What is VO2 Max?

Your VO2 can be defined as the amount of oxygen your body utilizes to produce energy at a given intensity. It is another way to express “energy cost.” While your body has multiple energy sources to support exercise, using oxygen (aerobic respiration) is the largest contributor. Anaerobic respiration is also always contributing, but is only dominant in the short bursts of peak effort. The end result of these two processes is the production of Adenosine Triphospate, or ATP (the fundamental currency of energy in the body). Aerobic (with oxygen) respiration begins anaerobically as glucose is broken down into pyruvate which then goes into an aerobic metabolic pathway inside the mitochondria (powerhouse organelle of the cell). This is a very efficient process that produces large amounts of ATP. During exercise your body’s rates of aerobic and anaerobic respiration increase. This continues until the oxygen available is insufficient for aerobic respiration to continue to dominate. When this happens there is a backup of pyruvate as the mitochondria can’t allow any more in because oxygen (the key component in the cycle) is unavailable. The pyruvate is instead converted to lactate. Lactate buffers the acidity of the environment by accepting the free hydrogen ions produced in the process of using the remaining ATP in the cell. If the exercise continues, lactate can be shifted back to aerobic type 1 muscle fibers to produce more energy aerobically. However, if the workload continues to increase the free hydrogen ions exceed the ability of lactate to buffer and the lactate production exceeds removal, rendering the environment increasingly acidic. This leads to acidosis, muscles burn, increased breathing and impending fatigue.

The byproduct aerobic respiration is water (H2O) and carbon dioxide (CO2). However, the byproduct of the anaerobic respiration is lactate. While the formation of lactate is helpful in keeping pH stable, it is removed to create another source of ATP production in type I endurance muscles or glucose production in the liver. But as you see, when exercise reaches sustained high-intensity the demand outperforms both energy pathways and acidosis results. We call the point at which the anaerobic system’s contribution increases and lactate production begins to climb over baseline the Aerobic Threshold. The point when the lactate production exceeds removal is called the Anaerobic Threshold. At this level the anaerobic system dominates, lactate is still being converted into more ATP aerobically, but the climbing acidity is driving you to your peak, forcing you to eventually stop. The amount of oxygen your body was using (measured in ml of O2 per kg of bodyweight per minute) is your VO2 Max. This is your maximum or peak aerobic performance.

When you train to increase VO2 Max you also train to increase the aerobic and anaerobic thresholds. This increase in aerobic efficiency not only delays fatigue, but has huge impacts on your longevity. While VO2 Max declines with age in adults, you can train to improve it by identifying these key thresholds and developing the right program. The results of the test will be printed out in a report that will provide these thresholds, the corresponding heartrates for plotting out training intensities and the corresponding calories burned per hour for planning nutrition.

Energy production in the cell when adequate oxygen is present:

Energy production in the cell when oxygen supply is inadequate: