Energy Systems of the Human Body

There are several energy systems in the human body that produce energy for working muscles. If you are an athlete, or are training athletes, knowing about these systems, how they work, and how to develop them is vital for success. By energy systems we are referring to how the body produces energy for physical activity.

This information is important because which system is involved will depend on the intensity and duration of the activity. Therefore, training needs to involve the development of these systems based on what is required in competition.

In addition, everyone will have a dominant energy producing system. Therefore, it would be absolutely ridiculous to take a long distance runner and try and make them into a sprinter.

The first system is the Adenosine Triphosphate (ATP) is the immediate source for energy that is stored in muscle cells. As the phosphate is broken down (there are 3 of them for each molecule of ATP) energy is released. This system is only good for very quick and powerful movements. Then, ATP runs out and much be re-synthesized so the process can be repeated. Oxygen is not required for this to work, there are no waste products, but it is extremely short in duration. This system will last for about 0.5 minutes. Sprinters have a very well developed ATP system.

The second system is the PC (PC is phosphocreatine) is a molecule found in muscles cells. Once ATP is broken down it will become Adenosine Diphosphate (ADP). At this point the PC will be broken down so the individual phosphates from the PC will join with the ADP to form ATP again. This is the re-synthesizing process of used up ATP. This system also requires no oxygen, and there are no waste products produced. But, it is very short in duration. This system lasts for about 0.5 to 1.5 minutes.

The third system is called the Anaerobic Glycolysis (lactic acid) System. This energy is obtained by breaking down glucose (either stored in muscles or from the blood stream). Through this process lactic acid (which causes the burning sensation) is produced. If the activity is too intense, and there is no time for the body to clear out the lactic acid, then the activity can not be maintained. This system lasts for about 1.5 to 3 minutes. Sports, such as gymnastics where routines last for about 2-4 minutes have well developed anaerobic glycolytic systems.

The fourth system is the Aerobic Glycolytic System, also called the Oxygen System. The main source of energy for this system is carbohydrates (from stores in muscles or from the blood stream) and fats (from stores). In order for this system to work there needs to be oxygen present, as it is part of the cycle. If oxygen is not present then this system simply will not work. The waste products are carbon dioxide (which we exhale) and water. This system, if the activity is not too intense, can continue indefinitely (assuming the body has glucose, fat, and oxygen. However, if the acuity is too intense then glucose may run out, and the body will produce lactic acid. This is referred to as oxygen deficit. Marathon runners have well developed aerobic systems. Sprinters usually don't, but they don't need to.

Systems which have short duration can be activated almost instantaneously and are very powerful. Where as the systems which last longer take more time to be activated and have less power.

Knowing what your athletes come with (usually because of genetics) will help guide them into the right activities. Although you can develop the ATP system in a long distance runner it will never be as good as someone who is a natural sprinter.

Also, no single system works by itself. All systems are in play all the time no matter what you are doing. The duration and intensity of the activity will determine which system is the one used primarily, but they are all used to some extent.