Sustained Isometric Wrist Flexion and Extension Maximal Voluntary Contractions on Corticospinal Excitability to Forearm Muscles during Low-Intensity Hand-Gripping.

Davis A Forman,Garrick N Forman,Bernadette A Murphy,Michael W R Holmes

doi:10.3390/brainsci10070445

Davis A Forman, Garrick N Forman + Show 2 more

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https://doi.org/10.3390/brainsci10070445

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Abstract

The wrist extensors demonstrate an earlier fatigue onset than the wrist flexors. However, it is currently unclear whether fatigue induces unique changes in muscle activity or corticospinal excitability between these muscle groups. The purpose of this study was to examine how sustained isometric wrist extension/flexion maximal voluntary contractions (MVCs) influence muscle activity and corticospinal excitability of the forearm. Corticospinal excitability to three wrist flexors and three wrist extensors were measured using motor evoked potentials (MEPs) elicited via transcranial magnetic stimulation. Responses were elicited while participants exerted 10% of their maximal handgrip force, before and after a sustained wrist flexion or extension MVC (performed on separate sessions). Post-fatigue measures were collected up to 10-min post-fatigue. Immediately post-fatigue, extensor muscle activity was significantly greater following the wrist flexion fatigue session, although corticospinal excitability (normalized to muscle activity) was greater on the wrist extension day. Responses were largely unchanged in the wrist flexors. However, for the flexor carpi ulnaris, normalized MEP amplitudes were significantly larger following wrist extension fatigue. These findings demonstrate that sustained isometric flexion/extension MVCs result in a complex reorganization of forearm muscle recruitment strategies during hand-gripping. Based on these findings, previously observed corticospinal behaviour following fatigue may not apply when the fatiguing task and measurement task are different.

Highlights

Traditionally defined as a reduced capacity to generate muscle force, fatigue is understood to be a symptom in which both physical and cognitive functions may be limited [1,2]. These limitations arise through interactions of perceived fatigability and performance fatigability; perceived fatigability refers to the subjective state of the individual, while performance fatigability is measured through objective laboratory-based assessments characterizing the functional decline of performance [3]
While results demonstrated that performance fatigability changed muscle activity in all forearm muscles the results demonstrated that performance fatigability changed muscle activity in all forearm musclesto some extent, these adaptations were more complex
The purpose of this study was accomplished by examining the influence of sustained isometric wrist flexion and extension maximal voluntary contractions (MVCs) on forearm muscle activity and corticospinal excitability during a separate motor task

Summary

Introduction

Traditionally defined as a reduced capacity to generate muscle force, fatigue is understood to be a symptom in which both physical and cognitive functions may be limited [1,2] These limitations arise through interactions of perceived fatigability and performance fatigability; perceived fatigability refers to the subjective state of the individual (and involves subjective measures), while performance fatigability is measured through objective laboratory-based assessments characterizing the functional decline of performance [3]. The findings of these studies apply well to sports and workplaces, where the same motor task is often performed long after it has induced performance impairments. It is less clear how the effects of performance fatigability induced in one motor task can manifest in another which shares similar muscle actions

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