Energy Systems

Human beings derive energy from the food they eat and they use that energy for repair, maintenance, growth and basic human function. The production of energy from various nutrients is what we commonly refer to as metabolism. Different chemical pathways are needed to break the food down for use in the cells which rely on the basic energy molecule of the body, ATP(adenosine triphosphate). This molecule consists of adenosine which is linked with 3 phosphate bonds. When the phosphate bonds are broken , a burst of energy is released and the ATP is then broken down into ADP(adenosine diphosphate). This occurs within the mitochondria of the cell. Obviously how energy is supplied in terms of human movement is of utmost importance in training athletes properly. ATP is a by product of the Krebs Cycle which is a complex series of chemical reactions in all cells that use oxygen as part of their respiration process. The Krebs Cycle produces carbon dioxide and ATP which is an energy rich compound. Energy from ATP is usually derived from the break down of glucose but can also be derived from fats and proteins as well. Glucose can pass through cell membranes so it is therefore able to transport energy from one part of the body to another. The Krebs Cycle is part of a metabolic pathway that chemically converts carbohydrates, fats and proteins into carbon dioxide and water to produce a form of usable energy.

There are three basic energy systems that the body uses to meet the demands of cardiovascular, strength, and endurance activities.

• The High Intensity Short Duration System - This produces energy from metabolic processes that rely on the phosphate compounds ATP (adenosine triphosphate) and CP (creatine phosphate). It is also known as the anaerobic energy system or ATP-CP system. This energy system can fuel intense effort for 20-30 seconds.
   
• The Intermediate Energy System - This is referred to as the glycolytic system, it is broken down into the oxygen independent glycolytic system and the oxygen dependent glycolytic system. This process breaks down and coverts glucose into pyruvic acid and ATP. The production of lactic acid also occurs here and serves as an additional source of energy. Once the ATP/CP reserves are exhausted the oxygen independent glycolytic system takes over and provides energy from 30 seconds to about 3 minutes. Glycogen is broken down in the liver and muscle without the use of oxygen. The oxygen dependent glycolytic system takes over after 3 minutes and can last over an hour. This system breaks down muscle and liver glycogen in the presence of oxygen but does not supply energy as quickly as the ATP/CP or the oxygen independent glycolytic systems do. It is also known as the aerobic energy system.
   
• The Long Term Energy System - This system uses carbohydrates that are stored in the muscles, liver and bloodstream and also uses fats and proteins as additional fuel sources. This is accomplished under oxidative conditions. Fat delivers the needed energy for resting muscles and the liver which also has obvious health implications for cleansing the body.

Although one energy system may be dominant in a specific activity, all 3 energy systems are used simultaneously during rigorous activity as these movements involve muscle action that simultaneously stabilize and move the limbs. Therefore the body may rely on the long term energy system for its overall movements and rely on the short term and intermediate systems for highly active muscle groups. The 3 basic energy systems are almost always at work and overlap each other. As the trainer you must know the dominant system that your athlete needs to excel in their respective sport. Fortunately Yuri Verkoshansky adapted it from a 1974 study done by Fox & Matthews and I have listed this synopsis below. The numbers appear as percentages that each system is approximately used each sport.