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The human body stores and converts our food into usable energy. Adenosine triphosphate (ATP) is a molecule that stores energy throughout the body for later use. Without ATP, muscle use and growth are not possible. The body utilizes one of three energy systems to convert our body’s ATP storage into usable energy. These three systems are the Phosphagen System, Glycolytic System, and Oxidative System.

The Phosphagen System is the primary source of ATP during exercises that are high intensity, explosive in nature, require maximal effort, and last a short period of time (up to 10 seconds). The Phosphagen Sytem is active in the first 10 seconds of all exercises. This system is anaerobic (it works in the absence of oxygen). Sprints, power-lifting, and Plyometrics (jumping) are examples of exercises that would force the body to utilize the Phosphagen System.

The Glycolytic System breaks down carbohydrates in the form of glucose to produce ATP during exercises that are sustained and intense, but not requiring maximal effort. Like the Phosphagen System, Glycolysis is also anaerobic . This system takes over 5-10 seconds after initiation of an activity (after the Phosphagen System) and stays active for up to three minutes. Wrestling is an example of an exercise that would force the body to utilize the Glycolytic System.

The Oxidative System is the primary source of ATP at rest and during long distance or low intensity activities. This system uses carbohydrates and fats as energy.

Unlike the two systems listed above, the Oxidative System is arobic (it requires oxygen). The Oxidative system usually takes over 3 minutes after the initiation of exercise. Marathon running and cross-country skiing are both examples of exercises that would force the body to utilize the Oxidative System.