Fatigue-related firing of distal muscle nociceptors reduces voluntary activation of proximal muscles of the same limb

J Appl Physiol (1985). 2014 Feb 15;116(4):385-94. doi: 10.1152/japplphysiol.01166.2013. Epub 2013 Dec 19.

Abstract

With fatiguing exercise, firing of group III/IV muscle afferents reduces voluntary activation and force of the exercised muscles. These afferents can also act across agonist/antagonist pairs, reducing voluntary activation and force in nonfatigued muscles. We hypothesized that maintained firing of group III/IV muscle afferents after a fatiguing adductor pollicis (AP) contraction would decrease voluntary activation and force of AP and ipsilateral elbow flexors. In two experiments (n = 10) we examined voluntary activation of AP and elbow flexors by measuring changes in superimposed twitches evoked by ulnar nerve stimulation and transcranial magnetic stimulation of the motor cortex, respectively. Inflation of a sphygmomanometer cuff after a 2-min AP maximal voluntary contraction (MVC) blocked circulation of the hand for 2 min and maintained firing of group III/IV muscle afferents. After a 2-min AP MVC, maximal AP voluntary activation was lower with than without ischemia (56.2 ± 17.7% vs. 76.3 ± 14.6%; mean ± SD; P < 0.05) as was force (40.3 ± 12.8% vs. 57.1 ± 13.8% peak MVC; P < 0.05). Likewise, after a 2-min AP MVC, elbow flexion voluntary activation was lower with than without ischemia (88.3 ± 7.5% vs. 93.6 ± 3.9%; P < 0.05) as was torque (80.2 ± 4.6% vs. 86.6 ± 1.0% peak MVC; P < 0.05). Pain during ischemia was reported as Moderate to Very Strong. Postfatigue firing of group III/IV muscle afferents from the hand decreased voluntary drive and force of AP. Moreover, this effect decreased voluntary drive and torque of proximal unfatigued muscles, the elbow flexors. Fatigue-sensitive group III/IV muscle nociceptors act to limit voluntary drive not only to fatigued muscles but also to unfatigued muscles within the same limb.

Keywords: group III and IV muscle afferents; muscle fatigue; superimposed twitch; transcranial magnetic stimulation; voluntary activation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Biomechanical Phenomena
  • Brachial Plexus / physiopathology
  • Electric Stimulation
  • Female
  • Humans
  • Ischemia / metabolism
  • Ischemia / physiopathology*
  • Male
  • Motor Cortex / physiopathology
  • Muscle Contraction*
  • Muscle Fatigue*
  • Muscle Strength
  • Muscle, Skeletal / blood supply
  • Muscle, Skeletal / innervation*
  • Nociceptors / metabolism*
  • Pain / metabolism
  • Pain / physiopathology
  • Regional Blood Flow
  • Time Factors
  • Transcranial Magnetic Stimulation
  • Ulnar Nerve / physiopathology
  • Upper Extremity