What Is Aerobic & Anaerobic Metabolism?

Your ability to work and live depends on your metabolism, or the ability of your cells to convert proteins, carbohydrates and fats into energy. Whereas aerobic metabolism requires oxygen, anaerobic metabolism takes place without oxygen. These dual processes are not isolated but typically work in concurrence. When you describe certain exercises as aerobic or anaerobic, you’re referring to the type of metabolism that predominates.

How Metabolism Works

The energy currency in your body is a compound called adenosine triphosphate, or ATP. This compound stores chemical energy from nutrients, such as your breakfast toast, in the bonds between the phosphates making up its structure. When ATP releases the energy from these bonds, your body can produce heat to meet various needs, such as muscle movement, digestion, respiration and circulation. The sum of all of your body’s energy processes is your metabolism, which is subdivided into aerobic and anaerobic processes.

Aerobic Versus Aerobic Metabolism

As your body breaks down glucose, a simple sugar molecule, in the first dozen steps, it produces a compound called pyruvate. When this compound enters the mitochondria, or powerhouse, of the cell, aerobic metabolism occurs in which this compound is oxidized and turned into carbon dioxide and water. In the case of anaerobic metabolism, pyruvate enters the fluid, or cytoplasm, of the cell and is turned into lactic acid via a process called glycolysis. While aerobic metabolism uses fat, protein and carbohydrates and can continue indefinitely, anaerobic metabolism uses only carbohydrates and doesn’t last long.

Difference in Efficiency

The amount of energy generated by anaerobic metabolism is less than one-tenth of what is produced by aerobic metabolism. When one glucose molecule is converted into lactic acid in anaerobic metabolism, three ATP molecules are generated. When a glucose molecule is converted into carbon dioxide and water via aerobic metabolism, it produces 39 molecules of ATP. However, glycolysis requires powerful enzymes that compensate for the lower energy efficiency of anaerobic metabolism. What limits the anaerobic process is the byproduct, or lactic acid. The accumulation of lactic acid in the muscles causes a burning sensation, pain and fatigue, slowing down athletes who perform anaerobic activities.

Aerobic Versus Anaerobic Activities

When you perform short and intense activities that require maximal energy, you rely on your anaerobic metabolism. For example, the energy used to run a 100-meter sprint is about 100 percent anaerobic. The primary nutrient for this type of exercise is carbohydrates. If you’re performing a low-intensity physical activity over a long period of time, such as running a marathon, you’ll draw the majority of ATP from aerobic metabolism. For these types of activities, fat becomes the chief fuel source. Some activities require the use of both types of metabolism. For example, if you’re cycling in a long distance race, your body will draw on your anaerobic metabolism for a short-term energy boost to climb a hill.