A comparison of central aspects of fatigue in submaximal and maximal voluntary contractions

Abstract

Magnetic and electrical stimulation at different levels of the neuraxis show that supraspinal and spinal factors limit force production in maximal isometric efforts ("central fatigue"). In sustained maximal contractions, motoneurons become less responsive to synaptic input and descending drive becomes suboptimal. Exercise-induced activity in group III and IV muscle afferents acts supraspinally to limit motor cortical output but does not alter motor cortical responses to transcranial magnetic stimulation. "Central" and "peripheral" fatigue develop more slowly during submaximal exercise. In sustained submaximal contractions, central fatigue occurs in brief maximal efforts even with a weak ongoing contraction (<15% maximum). The presence of central fatigue when much of the available motor pathway is not engaged suggests that afferent inputs contribute to reduce voluntary activation. Small-diameter muscle afferents are likely to be activated by local activity even in sustained weak contractions. During such contractions, it is difficult to measure central fatigue, which is best demonstrated in maximal efforts. To show central fatigue in submaximal contractions, changes in motor unit firing and force output need to be characterized simultaneously. Increasing central drive recruits new motor units, but the way this occurs is likely to depend on properties of the motoneurons and the inputs they receive in the task. It is unclear whether such factors impair force production for a set level of descending drive and thus represent central fatigue. The best indication that central fatigue is important during submaximal tasks is the disproportionate increase in subjects' perceived effort when maintaining a low target force.

Distinct profiles of neuromuscular fatigue during muscle contractions below and above the critical torque in humans

“…Central fatigue was present in trials performed both below and above the CT (measured as a reduction in voluntary activation and maximal AREMG), which suggests that, as a result of repetitive contractions, the subjects were unable to voluntarily drive the knee extensors to the same extent at the end of the trials as they were at the beginning (50). The present data cannot identify the location(s) of this impairment within the CNS, but a number of spinal and supraspinal mechanisms have been suggested (for review, see Ref.…”

“…Fatigue can be attributed to a variety of processes along the motor pathway, and these are typically defined as being of central or peripheral origin. Peripheral fatigue refers to processes that occur at or distal to the neuromuscular junction (i.e., within the contracting muscle), whereas central fatigue refers to processes occurring proximal to the neuromuscular junction [i.e., residing within the central nervous system (CNS) (50)]. Both can be quantified using electrical stimulation of the muscle group(s) of interest using the interpolated twitch technique during a maximal voluntary contraction (MVC) (8,24).…”

“…A reduction in torque in response to stimulation at rest following a MVC is representative of peripheral fatigue (10,13). Central fatigue is commonly quantified as a reduction in voluntary activation (24,25,50). The interpolated twitch technique has some important limitations (see Refs.…”

Parallels between astronauts and terrestrial patients – Taking physiotherapy rehabilitation “To infinity and beyond”

“…A common way of describing types of fatigue use the following categories: physiological (peripheral) and central fatigue (Taylor & Gandevia, 2008) though experienced fatigue has also been described in relation to people with NMDs . Fatigue in NMDs and other neurological conditions is known to be multi-factorial Kalkman et al, 2007) and may be of more concern for astronauts in long duration missions than current ISS missions.…”

Fadiga muscular entre séries de exercícios isocinéticos em mulheres jovens

“…A fadiga muscular pode ser definida como uma queda na capacidade de um músculo ou grupo muscular em gerar força (TAYLOR; GANDEVIA, 2008). Vários fatores como a massa muscular, o tipo de fibra muscular e a ativação muscular específica podem influenciar a fadiga (KENT-BRAUN et al, 2002).…”