PMID- 34473572
OWN - NLM
STAT- MEDLINE
DCOM- 20211029
LR  - 20211102
IS  - 1522-1601 (Electronic)
IS  - 0161-7567 (Linking)
VI  - 131
IP  - 4
DP  - 2021 Oct 1
TI  - Pain-induced changes in motor unit discharge depend on recruitment threshold and 
      contraction speed.
PG  - 1260-1271
LID - 10.1152/japplphysiol.01011.2020 [doi]
AB  - At high forces, the discharge rates of lower- and higher-threshold motor units 
      (MU) are influenced in a different way by muscle pain. These differential effects 
      may be particularly important for performing contractions at different speeds 
      since the proportion of lower- and higher-threshold MUs recruited varies with 
      contraction velocity. We investigated whether MU discharge and recruitment 
      strategies are differentially affected by pain depending on their recruitment 
      threshold (RT), across a range of contraction speeds. Participants performed 
      ankle dorsiflexion sinusoidal-isometric contractions at two frequencies (0.25 and 
      1 Hz) and two modulation amplitudes [5% and 10% of the maximum voluntary 
      contraction (MVC)] with a mean target torque of 20%MVC. High-density surface 
      electromyography recordings from the tibialis anterior muscle were decomposed and 
      the same MUs were tracked across painful (hypertonic saline injection) and 
      nonpainful conditions. Torque variability, mean discharge rate (MDR), DR 
      variability (DRvar), RT, and the delay between the cumulative spike train and the 
      resultant torque output (neuromechanical delay, NMD) were assessed. The average 
      RT was greater at faster contraction velocities (P = 0.01) but was not affected 
      by pain. At the fastest contraction speed, torque variability and DRvar were 
      reduced (P < 0.05) and MDR was maintained. Conversely, MDR decreased and DRvar 
      and NMD increased significantly during pain at slow contraction speeds (P < 
      0.05). These results show that reductions in contraction amplitude and increased 
      recruitment of higher-threshold MUs at fast contraction speeds appear to 
      compensate for the inhibitory effect of nociceptive inputs on lower-threshold 
      MUs, allowing the exertion of fast submaximal contractions during pain.NEW & 
      NOTEWORTHY Pain induces changes in motor performance, motor unit recruitment, and 
      rate coding behavior that varies across different contraction speeds. Here we 
      show that that pain reduces motor unit discharge rate and prolongs the 
      neuromechanical delay at slow contraction speeds only. This new evidence suggests 
      that there are differential nociceptive inhibitory effects across the motor unit 
      pool, which allows fast submaximal contractions to be exerted despite the 
      presence of pain.
FAU - Martinez-Valdes, Eduardo
AU  - Martinez-Valdes E
AUID- ORCID: 0000-0002-5790-7514
AD  - Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), School of Sport, 
      Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, 
      University of Birmingham, Birmingham, UK.
FAU - Negro, Francesco
AU  - Negro F
AUID- ORCID: 0000-0002-9094-8932
AD  - Department of Clinical and Experimental Sciences, Universita degli Studi di 
      Brescia, Brescia, Italy.
FAU - Arvanitidis, Michail
AU  - Arvanitidis M
AD  - Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), School of Sport, 
      Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, 
      University of Birmingham, Birmingham, UK.
FAU - Farina, Dario
AU  - Farina D
AUID- ORCID: 0000-0002-7883-2697
AD  - Department of Bioengineering, Imperial College London, London, United Kingdom.
FAU - Falla, Deborah
AU  - Falla D
AUID- ORCID: 0000-0003-1689-6190
AD  - Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), School of Sport, 
      Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, 
      University of Birmingham, Birmingham, UK.
LA  - eng
PT  - Journal Article
DEP - 20210902
PL  - United States
TA  - J Appl Physiol (1985)
JT  - Journal of applied physiology (Bethesda, Md. : 1985)
JID - 8502536
SB  - IM
MH  - Electromyography
MH  - Humans
MH  - Isometric Contraction
MH  - *Motor Neurons
MH  - Muscle Contraction
MH  - Muscle, Skeletal
MH  - Myalgia
MH  - *Patient Discharge
MH  - Recruitment, Neurophysiological
OTO - NOTNLM
OT  - discharge rate
OT  - hypertonic saline
OT  - motor unit
OT  - neuromechanical delay
OT  - pain
OT  - recruitment
EDAT- 2021/09/03 06:00
MHDA- 2021/10/30 06:00
CRDT- 2021/09/02 17:21
PHST- 2021/09/03 06:00 [pubmed]
PHST- 2021/10/30 06:00 [medline]
PHST- 2021/09/02 17:21 [entrez]
AID - 10.1152/japplphysiol.01011.2020 [doi]
PST - ppublish
SO  - J Appl Physiol (1985). 2021 Oct 1;131(4):1260-1271. doi: 
      10.1152/japplphysiol.01011.2020. Epub 2021 Sep 2.