Neural control in human muscle fatigue: changes in muscle afferents, moto neurones and moto cortical drive

To understand the neural factors which contribute to fatigue, it is not satisfactory to regard fatigue as occurring only when a task can no longer be performed. Changes in muscle afferent feedback, mote neuronal discharge, mote cortical output, and perceived effort develop well before an endurance limit in limb muscles. During sustained maximal contractions the discharge of mote neurones declines, commonly to below the level required to produce maximal force from the muscle whose contractile speed is usually slowed. Thus, some 'central' fatigue develops. Recent findings using transcranial stimulation have revealed that the mote cortex is one site at which suboptimal output develops during human muscle fatigue. There is a need to study the reflex effects on mote neurones and the excitability of the mote cortex in experimental animals, as well as to apply rigorous methods to assess these processes in voluntary exercise in human subjects.