The body is dependent upon two processes to create energy at rest and during exercise, aerobic and anaerobic metabolism. Simplified, the aerobic metabolic system uses oxygen, while the anaerobic system does not; however, oxygen plays a vital role in allowing the body to function under both systems.
Both the aerobic and anaerobic systems occur simultaneously; there is no switching from one to the other. Whether the aerobic or the anaerobic system is dominant depends on the amount of muscle oxygen available.
Muscle Oxygen
Muscle oxygen means the balance between how much oxygen is available and how much the muscle needs. For instance, if the supply is less than the demand, oxygen levels drop, and the muscle relies on anaerobic metabolism for energy. On the other hand, when the supply is greater than the demand, oxygen levels are high, allowing the muscle to use aerobic metabolism for energy.
Aerobic Metabolism
Aerobic metabolism fuels most of the energy needed for long duration activity. The aerobic metabolic system functions using the Krebs Cycle, a complex series of chemical reactions that use oxygen to convert nutrients (carbohydrates, fats, and protein) to carbon dioxide and adenosine triphosphate (ATP), an energy-rich compound.
Aerobic metabolism relies on the circulatory system to transport oxygen to the working muscles before it creates ATP. Aerobic metabolism is used primarily during endurance exercises which are typically less intense and can therefore continue for longer periods of time.
Anaerobic Metabolism
Anaerobic metabolism happens during short, intense exercise when the oxygen needs of muscles are greater than what the blood can supply, leading to oxygen debt. If this debt gets too high, the muscle can’t work properly. The only way to help the muscle recover is by supplying it with oxygen-rich blood to clear out the extra lactic acid. This usually occurs during the recovery phase of a workout.
Many people confuse the concepts of blood lactate and lactic acid. Lactate is produced as a byproduct of the energy system but is completely harmless; in fact, it is actually used as fuel by the heart and muscles. Even at rest, the body produces lactate, though quantities increase with exercise. Lactic acid, however, is a byproduct of lactate buildup and causes acidosis to increase in the system.
The Bottom Line
Oxygen plays a vital role in both the aerobic and anaerobic metabolic systems. While oxygen is required as a direct energy source in the aerobic system, it is also essential in clearing the blood of excess lactic acid buildup in the anaerobic system.
Image courtesy of Robert Tisserand
