Exercise Physiology (1918–1944)

Abstract

In 1918 little was known about the supply of energy to working muscles and nothing was known about the role of adenosine triphosphate (ATP) in muscle contraction. Neither was it known that the partial breakdown of sugars (glycolysis) can release energy when oxygen is lacking (via the formation of ATP). While studying oxygen uptake during exercise, Krogh and Lindhard came to wonder about the source of energy for muscular work. At the time, there were two schools of thought. In Germany, Nathan Zuntz and his students had found that muscles can utilize and convert into mechanical work a constant fraction of the energy liberated by combustion from any available substance—provided the substance can be oxidized in the body.¹ In contrast, the Cambridge school, represented by Walter M. Fletcher, Frederick G. Hopkins, Archibald V. Hill, and others, suggested that muscular contraction depended on the splitting of a definite molecule (unknown but closely allied to carbohydrate), resulting in the formation of lactic acid.² If the Cambridge school were correct, it seemed inconceivable to Krogh that substances such as fat could be utilized by the muscles without a chemical transformation involving the loss of energy.

The Three Musketeers.