Energy Systems - The Principle of Coupled Reactions

The Principle of Coupled Reactions

Since energy is released when ATP is broken down, energy is required to rebuild or resynthesize ATP. The building blocks of ATP synthesis are the by-products of its breakdown; adenosine diphosphate (ADP) and inorganic phosphate (Pi). The energy for ATP resynthesis comes from three different series of chemical reactions that take place within the body. Two of the three depend upon the food we eat, whereas the other depends upon a chemical compound called phosphocreatine. The energy released from any of these three series of reactions is coupled with the energy needs of the reaction that resynthesizes ATP. The separate reactions are functionally linked together in such a way that the energy released by the one is always used by the other.

There are 3 methods to resynthesize ATP:

• ATP-PC system (Phosphogen system) - This system is used only for very short durations of up to 10 seconds. The ATP-PC system neither uses oxygen nor produces lactic acid if oxygen is unavailable and is thus said to be alactic anaerobic. This is the primary system behind very short, powerful movements like a golf swing, a 100 m sprint or powerlifting.

• Anaerobic system (Lactic Acid system) - Predominates in supplying energy for exercises lasting less than 2 minutes. Also known as the Glycolytic System. An example of an activity of the intensity and duration that this system works under would be a 400 m sprint.

• Aerobic system - This is the long duration energy system. By 5 minutes of exercise the O₂ system is clearly the dominant system. In a 1 km run, this system is already providing approximately half the energy; in a marathon run it provides 98% or more.