Bioenergetics of Exercise and Training

Human activity, in its various forms, requires energy. Exercise involves the use of energy to perform work that propels the body. Training increases the efficiency of this process in various ways. Bioenergetics is the study of the formation, conversion, and use of energy in a biological system. Its application in sports relates to how three energy systems, (1) adenosine triphosphate (ATP)/creatine phosphate (CP), (2) glycolytic/nonoxidative, and (3) oxidative, are used.

Energy is stored in the body as fat, protein (muscle), and glycogen (liver and muscle). It becomes incorporated into the body via ingestion and digestion of food. And when it is metabolized by the three energy systems, the by-products include carbon dioxide and heat.

Different activities use various combinations of these three energy systems. For rapid-power activities (i.e., shot put, weight lifting) that last less than 3 or 4 seconds, the primary energy source is the ATP/CP system. For speed activities that last up to approximately 1 minute or less (e.g., 100-, 400-meter runs), the glycolytic/nonoxidative system uses primarily blood glucose and muscle glycogen. For endurance activities (running a mile or longer), the primary energy system will be oxidative, using muscle and liver glycogen, lipids, and amino acids.

Many activities, of course, use various combinations of the three energy systems, more so than others, responding to the constantly shifting demands of the athlete. A soccer player, for example, will constantly be using the oxidative system to keep running during the game. But sometimes, a sprint may be required to defend or attack, and that effort will tap into the nonoxidative glycolytic system. All three systems are always active, however, with the body constantly replenishing their supply of energy and regulating its use.