A Brief History of Exercise Metabolism

Abstract

The source of energy utilized during physical activity has been of intense scientific interest for at least two centuries. This chapter briefly describes how (and why) each of the three major macronutrients—i.e., protein, carbohydrate, and fat—has alternately had their moments in the sun. Specifically, although until the 1860s protein was considered to be the only fuel used during exercise, first carbohydrate, then fat, and then again carbohydrate held sway from the 1860s until World War II, from World War II until the late 1960s, and from the late 1960s to ca. 1990, respectively. It is now widely recognized, however, that contracting muscle relies upon a mixture of carbohydrate, fat, and even a small amount of protein to provide its energy needs, with the relative importance of each varying with the exercise intensity and duration, the characteristics (e.g., nutritional state, physical fitness) of the individual, etc. Thus, although substrate metabolism during exercise is now understood in greater detail than ever before, the overall picture has come full circle to that described by Zuntz at the start of the twentieth century.