Articles in PresS. J Appl Physiol (December 19, 2013). doi:10.1152/japplphysiol.01166.2013
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Fatigue-related firing of distal muscle nociceptors reduces voluntary
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activation of proximal muscles of the same limb
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David S Kennedy 1,2, Chris J McNeil 1,3, Simon C Gandevia 1,2, Janet L Taylor 1,2
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South Wales, Kensington, NSW, Australia; 3 School of Health & Exercise Sciences,
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University of British Columbia, Kelowna, BC, Canada
Neuroscience Research Australia, Randwick, NSW, Australia; 2 The University of New
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Running head:
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Distal muscle afferents reduce drive to proximal muscles
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Corresponding author: Associate Professor Janet Taylor Neuroscience Research Australia PO Box 1165 Randwick NSW 2031 Australia
[email protected] Copyright © 2013 by the American Physiological Society.
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ABSTRACT
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With fatiguing exercise, firing of group III/IV muscle afferents reduces voluntary activation and
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force of the exercised muscles. These afferents can also act across agonist/antagonist pairs,
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reducing voluntary activation and force in non-fatigued muscles. We hypothesized that
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maintained firing of group III/IV muscle afferents after a fatiguing adductor pollicis (AP)
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contraction would decrease voluntary activation and force of AP and ipsilateral elbow flexors. In
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two experiments (n=10), we examined voluntary activation of AP and elbow flexors by
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measuring changes in superimposed twitches evoked by ulnar nerve stimulation and transcranial
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magnetic stimulation of the motor cortex, respectively. Inflation of a sphygmomanometer cuff
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after a 2-min AP maximal voluntary contraction (MVC) blocked circulation of the hand for 2
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min and maintained firing of group III/IV muscle afferents. After a 2-min AP MVC, maximal
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AP voluntary activation was lower with than without ischemia (56.2±17.7% versus 76.3±14.6%;
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mean±SD; P