AJ-5-Physiology-of-the-human-body

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HUMAN ENERGY SYSTEMS

To achieve optimum performance in your workout or sport it is essential that you understand how your body produces the energy that makes you go. When we talk about the body's energy systems we are really talking about the chemical reactions that take place in your body (muscles) involving ATP, or Adenosine Triphosphate. In order for the body to produce energy it must cleave (chemically separate) a phosphate molecule from ATP which causes a release of energy. After the phosphate molecule is cleaved, ATP becomes ADP, or Adenosine Diphosphate, and will need to have another phosphate attached to be able to once again produce energy. The ability of the body to produce energy for activities is, therefore, dependent upon ATP and the replenishing thereof. The human body has three basic energy systems that are responsible for replenishing ATP. Two of these systems are anaerobic, which means without oxygen, and the other is aerobic, which means with oxygen. The ATP-CP system is the first of the anaerobic energy systems. As ATP is used it can quickly be replaced through a chemical reaction with Creatine Phosphate. Figure 1 is the actual chemical reaction where ATP is cleaved to produce energy and is then replenished by a reaction with Creatine Phosphate.

The ATP-CP system is active at the beginning of all forms of activities but is especially important in high intensity exercises. The source of fuel for the ATP-CP system is ATP and CP that is stored in the muscles and since only a small quantity can be stored, this energy source is only effective for activities that last ten seconds or less.

The second anaerobic energy system is called Anaerobic Glycolysis, but is commonly referred to as the lactic acid system because it produces lactic acid as a byproduct. The Anaerobic Glycolysis system is important in moderately high intensity exercises that generally last less than two minutes. Anaerobic Glycolysis works in conjunction with the other two energy systems but can be thought of as picking up where the ATP-PC system leaves off. The source of fuel for Anaerobic Glycolysis is either glucose from the blood or stored glucose and is therefore generally effective for activities lasting two minutes or less.

The third energy system is the Oxidative system, which involves the use of oxygen. This system picks up where the Anaerobic Glycolysis system leaves off and is generally involved after an activity has lasted longer than two minutes. The Oxidative system can use protein, fats, or carbohydrates as the source for energy but carbohydrates are the most efficient source for fuel. The ability of the Oxidative system to be able to use protein, fats, and carbohydrates as fuel is in contrast to the Anaerobic Glycolysis system and the ATP-PC system which can only use Glycogen or stored Creatine Phosphate.

The most important thing to understand about the body's different energy systems is that the intensity of exercise dictates the primary system that is involved. Figure 2 shows the different energy systems and generally when each system is involved based on the intensity of exercise as defined by length of time. It is also important to understand that most activities will involve more than one system but each system has a specific role to fulfill based upon the requirements of the activity.