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Lookup NU author(s): Dr Callum BrownsteinORCiD
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
The physiological mechanisms determining the progressive decline in the maximal muscle torque production capacity during isometric contractions to task failure are known to depend on task demands. Task-specificity of the associated adjustments in motor unit discharge rate (MUDR), however, remains unclear. This study examined MUDR adjustments during different submaximal isometric knee extension tasks to failure. Participants performed a sustained and an intermittent task at 20% and 50% of maximal voluntary torque (MVT), respectively (Experiment 1). High-density surface EMG signals were recorded from vastus lateralis (VL) and medialis (VM) and decomposed into individual MU discharge timings, with the identified MUs tracked from recruitment to task failure. MUDR was quantified and normalised to intervals of 10% of contraction time (CT). MUDR of both muscles exhibited distinct modulation patterns in each task. During the 20% MVT sustained task, MUDR decreased until ∼50% CT, after which it gradually returned to baseline. Conversely, during the 50% MVT intermittent task, MUDR remained stable until ∼40–50% CT, after which it started to continually increase until task failure. To explore the effect of contraction intensity on the observed patterns, VL and VM MUDR was quantified during sustained contractions at 30% and 50% MVT (Experiment 2). During the 30% MVT sustained task, MUDR remained stable until ∼80–90% CT in both muscles, after which it continually increased until task failure. During the 50% MVT sustained task the increase in MUDR occurred earlier, after ∼70–80% CT. Our results suggest that adjustments in MUDR during submaximal isometric contractions to failure are contraction modality- and intensity-dependent.
Author(s): Valenčič T, Ansdell P, Brownstein CG, Spillane PM, Holobar A, Škarabot S
Publication type: Article
Publication status: Published
Journal: The Journal of Physiology
Year: 2024
Pages: epub ahead of print
Online publication date: 15/04/2024
Acceptance date: 25/03/2024
Date deposited: 01/05/2024
ISSN (print): 0022-3751
ISSN (electronic): 1469-7793
Publisher: Wiley-Blackwell Publishing Ltd.
URL: https://doi.org/10.1113/JP286143
DOI: 10.1113/JP286143
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