The Journal of Physiology - 2022 - Mesquita - Effects of reciprocal inhibition and whole‐body relaxation on persistent.pdf (2.57 MB)
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Effects of reciprocal inhibition and whole‐body relaxation on persistent inward currents estimated by two different methods

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journal contribution
posted on 21.04.2022, 10:29 authored by Ricardo NO Mesquita, Janet L Taylor, Gabriel S Trajano, Jakob SkarabotJakob Skarabot, Aleš Holobar, Basílio AM Gonçalves, Anthony J Blazevich

Persistent inward currents (PICs) are crucial for initiation, acceleration, and maintenance of motoneuron firing. As PICs are highly sensitive to synaptic inhibition and facilitated by serotonin and noradrenaline, we hypothesised that both reciprocal inhibition (RI) induced by antagonist nerve stimulation and whole-body relaxation (WBR) would reduce PICs in humans. To test this, we estimated PICs using the well-established paired motor unit (MU) technique. High-density surface electromyograms were recorded from gastrocnemius medialis during voluntary, isometric 20-s ramp, plantarflexor contractions and decomposed into MU discharges to calculate delta frequency (ΔF). Moreover, another technique (VibStim), which evokes involuntary contractions proposed to result from PIC activation, was used. Plantarflexion torque and soleus activity were recorded during 33-s Achilles tendon vibration and simultaneous 20-Hz bouts of neuromuscular electrical stimulation (NMES) of triceps surae. ΔF was decreased by RI (n = 15, 5 females) and WBR (n = 15, 7 females). In VibStim, torque during vibration at the end of NMES and sustained post-vibration torque were reduced by WBR (n = 19, 10 females), while other variables remained unchanged. All VibStim variables remained unaltered in RI (n = 20, 10 females). Analysis of multiple human MUs in this study demonstrates the ability of local, focused inhibition to attenuate the effects of PICs on motoneuron output during voluntary motor control. Moreover, it shows the potential to reduce PICs through non-pharmacological, neuromodulatory interventions such as WBR. The absence of a consistent effect in VibStim might be explained by a floor effect resulting from low-magnitude involuntary torque combined with the negative effects of the interventions.

Funding

Versus Arthritis Foundation Fellowship (ref: 4422569)

Slovenian Research Agency (project J2-1731 and Programme funding P2-0041)

History

School

  • Sport, Exercise and Health Sciences

Published in

The Journal of Physiology

Volume

600

Issue

11

Pages

2765 - 2787

Publisher

Wiley

Version

VoR (Version of Record)

Rights holder

© The Authors

Publisher statement

This is an Open Access Article. It is published by Wiley under the Creative Commons Attribution 4.0 International Licence (CC BY). Full details of this licence are available at: https://creativecommons.org/licenses/by/4.0/

Acceptance date

13/04/2022

Publication date

2022-05-19

Copyright date

2022

ISSN

0022-3751

eISSN

1469-7793

Language

en

Depositor

Dr Jakob Skarabot. Deposit date: 19 April 2022