Design and performance of muscular systems: An overview

Abstract

For a general physiologist, A.V. Hill's definition that 'muscle is a machine that converts chemical to mechanical energy at constant temperature' is still a valid concept. But it is clearly not sufficient to tell us how muscles are used to perform a variety of different functions, such as locomotion, pumping blood through the circulation or air into the lung, or even catching prey and ingesting food. Muscles must be organized in a proper way, they must be operated in a well controlled fashion, and they need fuel which must be supplied according to needs. The 'muscular system' can thus be defined as the concerted action of molecular events permitting the generation of mechanical force, with the biochemical and physiological functions of energy supply under the control of the nervous systems. Because of the dependence of all parts of the system on all others, any part can in principle limit the performance of the entire system. One important question is therefore to see how the various parts react when the demands on the system are altered, in other words, to see how malleable the system is.