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Lookup NU author(s): Dr Callum BrownsteinORCiD
This is the authors' accepted manuscript of an article that has been published in its final definitive form by American Physiological Society, 2021.
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Cervicomedullary stimulation provides a means of assessing motoneuron excitability. Previous studies demonstrated that during low-intensity sustained contractions, small cervicomedullary evoked potentials (CMEPs) conditioned using transcranial magnetic stimulation (TMS-CMEPs) are reduced, whereas large TMS-CMEPs are less affected. As small TMS-CMEPs recruit motoneurons most active during low-intensity contractions whereas large TMS-CMEPs recruit a high proportion of motoneurons inactive during the task, these results suggest that reductions in motoneuron excitability could be dependent on repetitive activation. To further test this hypothesis, this study assessed changes in small and large TMS-CMEPs across low- and high-intensity contractions. Twelve participants performed a sustained isometric contraction of the elbow flexor for 4.5 min at the electromyography (EMG) level associated with 20% maximal voluntary contraction force (MVC; low intensity) and 70% MVC (high intensity). Small and large TMS-CMEPs with amplitudes of ∼15% and ∼50% Mmax at baseline, respectively, were delivered every minute throughout the tasks. Recovery measures were taken at 1-, 2.5- and 4-min postexercise. During the low-intensity trial, small TMS-CMEPs were reduced at 2-4 min (P ≤ 0.049) by up to -10% Mmax, whereas large TMS-CMEPs remained unchanged (P ≥ 0.16). During the high-intensity trial, small and large TMS-CMEPs were reduced at all time points (P < 0.01) by up to -14% and -33% Mmax, respectively, and remained below baseline during all recovery measures (P ≤ 0.02). TMS-CMEPs were unchanged relative to baseline during recovery following the low-intensity trial (P ≥ 0.24). These results provide novel insight into motoneuron excitability during and following sustained contractions at different intensities and suggest that contraction-induced reductions in motoneuron excitability depend on repetitive activation.
Author(s): Brownstein CG, Espeit L, Royer N, Ansdell P, Skarabot J, Souron R, Lapole T, Millet GY
Publication type: Article
Publication status: Published
Journal: Journal of Neurophysiology
Year: 2021
Volume: 125
Issue: 5
Pages: 1636-1646
Print publication date: 01/05/2021
Online publication date: 30/04/2021
Acceptance date: 25/03/2021
Date deposited: 08/05/2024
ISSN (print): 0022-3077
ISSN (electronic): 1522-1598
Publisher: American Physiological Society
URL: https://doi.org/10.1152/jn.00070.2021
DOI: 10.1152/jn.00070.2021
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