The idea that muscle function and, in fact, the function of all living tissues may be described by physical laws appeared in the second half of the 19th century. During this period, Helmoltz (Uber die Erhaltung der Kraft, 1847) showed that the principle of energy conservation may be applied to living systems. In the field of exercise physiology, this idea has been subsequently developed by Rodolfo Margaria's (1901-1983) School and the mathematical formalization of the theory has succeeded in the bioenergetic model. During the last 20 years methodical and critical study of the bioenergetic model has been carried out by Paolo Cerretelli, one of the most important heirs of Rodolfo Margaria's School. Original results and technological developments have been generated by his activity and many young scientists have been educated in this approach. The present paper wants to present the modern history of the bioenergetic model and is dedicated to Paolo Cerretelli on the occasion of his seventieth birthday.