Your body is in constant need of energy, because without it, your body wouldn't be able to perform physiological tasks it is required to do to survive. The ACE Group Fitness Instructor Manual states that energy, in the form of adenosine triphosphate, or ATP, is necessary for muscle activity, nerve conduction and all the chemical processes that make up your metabolism. Proper exercise depends on a sufficient source of energy, and understanding how the body produces energy will allow you to optimize your workouts.
The Phosphagen System
The phosphagen system consists of ATP and creatine phosphate, or CP. This system produces ATP through the breakdown of CP and is actually the quickest method of producing energy. Because energy production through the phosphagen system is quick, it is ideal for strenuous "all-out" activity. But because there is only a limited supply in your muscles, it can only create energy for roughly 10 seconds.
The Anaerobic System
The anaerobic system is the second quickest way your body synthesizes energy. By breaking down glucose from carbohydrates through a system called glycolysis, your body produces ATP. Like the phosphagen system, this system also produces ATP quickly but has access to a larger energy source through carbohydrates, allowing you to perform high-intensity activities for a longer duration. A downside is that the anaerobic system also creates a byproduct called lactate, which can cause muscle fatigue when levels get too high. Therefore, according to the NASM Essentials of Personal Fitness Training, this system is limited to roughly 30 to 50 seconds of activity.
The Aerobic System
Aerobic simply means "with oxygen," and as the name implies, this system uses oxygen in the formation of ATP. The process breaks down both carbohydrates and fat to create a large amount of ATP but is limited to how much oxygen is supplied to the cells. The aerobic system provides a lot of ATP over a longer period of time, making it the main source of energy for lengthy endurance exercises such as jogging.
Energy from Protein
In addition to creatine phosphate, carbohydrates and fat, your body can also utilize protein as an energy source. Protein provides just as much energy as carbohydrates but is utilized only when there are no more carbohydrates or fat. Your body would rather use protein for developing muscles and various body parts, activating enzymes and for carrying and delivering molecular compounds throughout the body. For this reason your body will only use protein as a source of energy when facing severe conditions such as starvation.
References
- "NASM Essentials of Personal Fitness Training"; National Academy of Sports Medicine; April 2007
- "ACE Group Fitness Instructor Manual"; American Council on Exercise; March 2007
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