ABSTRACT

The immediate source of energy for muscle activity within each cell is adenosine triphosphate (ATP). Muscle action is an organized composite of the action of individual cells. ATP is an intracellular substance which contains three phosphate molecules, and it is through the breakdown of the terminal phosphate that energy is produced. The amount of ATP available in each cell is very small, and only provides sufficient energy to last less than 1-2 seconds in an exhaustive sprint-like exercise. However, the cell attempts to maintain a fairly constant level of ATP, especially during moderate activities. The protein which helps to provide an immediate source of ATP is the molecule phosphocreatine phosphate (PCr). PCr phosphorylates (i.e., adds one phosphate) adenosine diphosphate (ADP) to form ATP. The amount of ATP and PCr combined however, lasts less than about 10 seconds in an exhaustive exercise. The long range source of energy for the cell comes from two main processes that involve utilizing the energy stored in foodstuffs. These two processes are:

(1) Glycolysis. ATP is produced anaerobically (without oxygen) from sugar derived from stored muscle glycogen. Glycogen is a polysaccharide (i.e., it consists of many sugars) molecule consisting of hundreds to thousands of glucose molecules linked together. Anaerobic exercise produces lactic acid which can accumulate and have adverse effects on performance. However, the anaerobic process does provide ATP when the body needs it as a quick source of energy (i.e., for sprint-like exercise).