The Fuel of Muscular Exercise

There are three major types of foodstuffs which can be oxidized in the body, namely: carbohydrates, fats, and proteins. Our problem is to determine the relative importance of each of these as a source of energy for muscular work of varying degrees of intensity and duration. This problem is complicated by the fact that a considerable amount of interconversion of the major foodstuffs occurs in the body. A common example of this process is the conversion of carbohydrate into fat in the commercial "fattening" of livestock. It is now believed that carbohydrates and fats are mutually interconvertible in the body and that the amino acids which make up the protein molecule are likewise capable, after certain metabolic modifications, of being converted to carbohydrate.

This makes it difficult to draw conclusions about oxidative sources of energy from a simple analysis of the constituents of the diet and necessitates the use of indirect methods of study.

A knowledge of the types of foodstuffs undergoing oxidation during muscular exertion is not only important from a nutritional standpoint, but is essential to a clear understanding of the chemical basis of muscle contraction anti of the resulting energy liberation. The experimental investigation of this fundamental problem is still far from complete and quite divergent results have been obtained by different workers.