Neurobiology of muscle fatigue

Abstract

Muscle fatigue encompasses a class of acute effects that impair motor performance. The mechanisms that can produce fatigue involve all elements of the motor system, from a failure of the formulation of the descending drive provided by suprasegmental centers to a reduction in the activity of the contractile proteins. We propose four themes that provide a basis for the systematic evaluation of the neural and neuromuscular fatigue mechanisms: 1) task dependency to identify the conditions that activate the various mechanisms; 2) force-fatigability relationship to explore the interaction between the mechanisms that results in a hyperbolic relationship between force and endurance time; 3) muscle wisdom to examine the association among a concurrent decline in force, relaxation rate, and motor neuron discharge that results in an optimization of force; and 4) sense of effort to determine the role of effort in the impairment of performance. On the basis of this perspective with an emphasis on neural mechanisms, we suggest a number of experiments to advance our understanding of the neurobiology of muscle fatigue.

Fatores clínicos, funcionais e inflamatórios associados à fadiga muscular e à fadiga autopercebida em idosas da comunidade

“…Muscle fatigue can be defined as the reduction, induced by the capacity of the neuromuscular system to generate strength, work or power 1,3,4 . Its setup may be related to neurological, metabolic, electrophysiological, mechanical, subjective among others, which interfere in the synchronous functioning between the central nervous system (CNS) and the peripheral paths 5,6 .…”

Shifting of activation center in the brain during muscle fatigue: An explanation of minimal central fatigue?

“…Muscle fatigue can be categorized as being of central or peripheral origin, with a majority of cases involving both (Gandevia, 2001). Although mechanisms that contribute to muscle fatigue have been studied extensively (review: Enoka and Stuart, 1992;Fitts, 1994), the role of cortical centers in contributing to fatigue during voluntary motor tasks (e.g., whether the brain is able to generate constant descending commands) or in modulating muscle fatigue is still largely unknown.…”

Changes in oxygen uptake, shoulder muscles activity, and propulsion cycle timing during strenuous wheelchair exercise

“…This adaptation has been proposed by previous authors during fatiguing exercises and is referred to as muscle wisdom. 33,34 Heavy exercise Several changes were observed during the heavy exercise bout, which may be attributed to fatigue.…”

“…The increase of the relaxation half-time previously observed during fatiguing exercise may have caused the increased activation time during the wheelchair exercise. 33,58,59 A reduction of calcium pump activity of the sarcoplasmic reticulum 59,60 resulting from an accumulation of inorganic phosphate 61 or changes in the action potential shape 62 are the most plausible explanations for the decline of the relaxation half-time. These two alterations also contribute to an increase in RMS and a decrease in MPF, electromyographical changes observed in our study.…”