Firing patterns of low-threshold trapezius motor units in feedback-controlled contractions and vocational motor activities

Experimental Brain Research
C WestadR H Westgaard

Abstract

The study aimed to examine firing patterns of low-threshold trapezius motor units, with attention given to motor unit recruitment threshold. Different motor tasks were explored: shoulder elevation, arm movement in typing, and the motor response to mental stress. Contraction amplitudes in the range from 1 to 10% of the surface electromyographic (SEMG) signal at maximal voluntary contraction (1-10% EMGmax) were studied, representing the range of trapezius muscle activity commonly observed in daily living. Single motor unit activity was recorded by a quadrifilar fine-wire electrode. A surface electrode simultaneously recorded the SEMG signal. Low-threshold motor units showed a small increase in mean firing rate, from 10.5 to 12.5 pulses per second ( p<0.01), in constant-amplitude contractions when SEMG amplitude increased from <2% to >4% EMGmax. After the first few minutes, firing rates were similar for all motor units in a contraction, despite different recruitment thresholds. Firing rates of motor units with threshold <2% EMGmax were the same in constant-amplitude contractions, contractions with vocational arm movement, and contractions with imposed stress for SEMG amplitude at the same level. High-frequency firing patterns were...Continue Reading

Citations

Jul 28, 2006·Experimental Brain Research·Rolf H WestgaardChristian Westad
Jul 27, 2007·European Journal of Applied Physiology·Paul Jarle Mork, Rolf H Westgaard
Dec 21, 2011·Journal of Neural Engineering·C J De Luca, J C Kline
Jan 21, 2010·Journal of Clinical Neurophysiology : Official Publication of the American Electroencephalographic Society·Jennifer L Stephenson, Katrina S Maluf
Mar 5, 2010·The Journal of Orthopaedic and Sports Physical Therapy·Joy L LongJames E Carpenter
Jun 15, 2012·Pain Medicine : the Official Journal of the American Academy of Pain Medicine·Hong-You GePascal Madeleine
Nov 20, 2012·Human Movement Science·Laurent BensoussanChristiane Rossi-Durand
Jul 14, 2010·Journal of Electromyography and Kinesiology : Official Journal of the International Society of Electrophysiological Kinesiology·Pernille VedstedGisela Sjøgaard
Dec 4, 2010·European Journal of Pain : EJP·Ellen WakefieldPaul J Mork
Jul 13, 2014·Experimental Physiology·Michael A PascoeRoger M Enoka
Nov 19, 2014·Frontiers in Human Neuroscience·Karen SøgaardGisela Sjøgaard

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