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Changes in motor unit behavior following isometric fatigue of the first dorsal interosseous muscle.

Authors: 

Lara McManus, Xiaogang Hu, William Rymer, Madeleine Lowery, Nina Suresh

Publication Type: 
Refereed Original Article
Abstract: 
Changes in motor unit behavior following isometric fatigue of the first dorsal interosseous muscle. J Neurophysiol 113: 3186–3196, 2015. First published March 11, 2015; doi:10.1152/jn.00146.2015.β€”The neuromuscular strategies employed to compensate for fatigue-induced muscle force deficits are not clearly understood. This study utilizes surface electromyography (sEMG) together with recordings of a population of individual motor unit action potentials (MUAPs) to investigate potential compensatory alterations in motor unit (MU) behavior immediately following a sustained fatiguing contraction and after a recovery period. EMG activity was recorded during abduction of the first dorsal interosseous in 12 subjects at 20% maximum voluntary contraction (MVC), before and directly after a 30% MVC fatiguing contraction to task failure, with additional 20% MVC contractions following a 10-min rest. The amplitude, duration and mean firing rate (MFR) of MUAPs extracted with a sEMG decomposition system were analyzed, together with sEMG root-mean-square (RMS) amplitude and median frequency (MPF). MUAP duration and amplitude increased immediately postfatigue and were correlated with changes to sEMG MPF and RMS, respectively. After 10 min, MUAP duration and sEMG MPF recovered to prefatigue values but MUAP amplitude and sEMG RMS remained elevated. MU MFR and recruitment thresholds decreased postfatigue and recovered following rest. The increase in MUAP and sEMG amplitude likely reflects recruitment of larger MUs, while recruitment compression is an additional compensatory strategy directly postfatigue. Recovery of MU MFR in parallel with MUAP duration suggests a possible role for metabolically sensitive afferents in MFR depression postfatigue. This study provides insight into fatigue-induced neuromuscular changes by examining the properties of a large population of concurrently recorded single MUs and outlines possible compensatory strategies involving alterations in MU recruitment and MFR
Digital Object Identifer (DOI): 
10.1152/jn.00146.2015
Publication Status: 
Published
Date Accepted for Publication: 
Friday, 13 February, 2015
Publication Date: 
11/03/2015
Journal: 
J Neurophysiol 113: 3186–3196, 2015.
Volume: 
113
Issue: 
2015
Pages: 
3186–3196
Research Group: 
Institution: 
National University of Ireland, Dublin (UCD)
Project Acknowledges: 
Open access repository: 
No