Chapter 9 Basic mechanisms of muscle fatigue in humans

Publisher As a first step in the analysis of fatigue, it is both convenient and logical to divide the possible causal mechanisms into two groups. One group consists of those factors that ultimately reduce the discharge of impulses to the muscles, by the motor neurons, and are, therefore, responsible for “central” fatigue. The other influences are those that interfere with the ability of the muscle fibers to respond fully to the motor neuron discharge, and thereby cause “peripheral” fatigue. This chapter discusses the areas that are expected to have special interest for the clinical neurophysiologist. The chapter includes the observations of historical significance as well as the results of contemporary studies. The motor cortex is an obvious candidate, as a site of central fatigue, and this possibility has been tested by magnetic stimulation. Peripheral fatigue occurs because of failure, either of the coupling mechanism between the action potential and the contractile machinery or of the contractile machinery itself. It is possible that there are other points of failure in peripheral fatigue and various studies have suggested that rises in the intracellular concentration of H+, inorganic P, diprotonated phosphate, and Mg2+ may all play a role.