The role of motor unit rate modulation versus recruitment in repeated submaximal voluntary contractions performed by control and spinal cord injured subjects

Journal of Electromyography and Kinesiology : Official Journal of the International Society of Electrophysiological Kinesiology
Christine K Thomas, Alejandro Del Valle

Abstract

The relative roles of motor unit firing rate modulation and recruitment were evaluated when individuals with cervical spinal cord injury (SCI) and able-bodied controls performed a brief (6 s), 50% maximal voluntary contraction (50% MVC; target contraction) of triceps brachii every 10 s until it required maximal effort to achieve the target force. Mean (+/-SD) endurance times for SCI and control subjects were 34+/-26 and 15+/-5 min, respectively, at which point significant reductions in maximal triceps force had occurred. Twitch occlusion analysis in controls indicated that force declines resulted largely from peripheral contractile failure. In SCI subjects, triceps surface EMG and motor unit potential amplitude declined in parallel suggesting failure at axon branch points and/or alterations in muscle membrane properties. The force of low threshold units, measured by spike-triggered averaging, declined in SCI but not control subjects, suggesting that higher threshold units fatigued in controls. Central fatigue was also obvious after SCI. Mean (+/-SD) MVC motor unit firing rates declined significantly with fatigue for control (24.6+/-7.1 to 17.3+/-5.1Hz), but not SCI subjects (25.9+/-12.7 to 20.1+/-9.7Hz). Unit firing rates were ...Continue Reading

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Citations

Jan 11, 2001·Muscle & Nerve·R M Enoka, A J Fuglevand
Jul 20, 2005·Experimental Brain Research·Gail F KoshlandBecky Farley
Dec 21, 2011·Journal of Neural Engineering·C J De Luca, J C Kline
Jul 1, 2006·Journal of Applied Physiology·Richard K ShieldsKeith R Cole
May 26, 2011·The Journal of Physiology·Christopher K ThompsonT George Hornby
Jul 31, 2013·Muscle & Nerve·Jason M DefreitasMatt S Stock
Aug 2, 2013·Acta Physiologica·C K ThomasI Zijdewind
Sep 17, 2014·Experimental Brain Research·Nina L SureshW Z Rymer
Nov 4, 2004·Canadian Journal of Physiology and Pharmacology·Alejandro Del Valle, Christine K Thomas
Apr 25, 2006·Muscle & Nerve·Richard K ShieldsCheng-Hsiang Lin
Dec 30, 2006·Muscle & Nerve·Michael A NordstromDouglas G Stuart
Aug 29, 2007·Muscle & Nerve·Maritha Indurthy, Lisa Griffin
Aug 5, 2008·Journal of Clinical Neurophysiology : Official Publication of the American Electroencephalographic Society·Brigitte WirthArmin Curt
Jun 24, 2005·Muscle & Nerve·Alejandro Del Valle, Christine K Thomas
Jul 19, 2005·Muscle & Nerve·Christine K Thomas, Inge Zijdewind
Nov 4, 2005·Journal of Neurophysiology·C K ThomasB Bigland-Ritchie
Mar 4, 2003·Journal of Neurophysiology·Inge Zijdewind, Christine K Thomas
Jul 15, 2006·American Journal of Physiology. Regulatory, Integrative and Comparative Physiology·Matthew W BundlePeter G Weyand
Jun 11, 2016·Journal of Applied Physiology·Brianna L CowlingCharles L Rice
Oct 23, 2002·Journal of Applied Physiology·Sandra K Hunter, Roger M Enoka
Nov 23, 2007·Journal of Applied Physiology·Janet L Taylor, Simon C Gandevia
Dec 14, 2012·Journal of Neurophysiology·Paola Contessa, Carlo J De Luca

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