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Muscle pain from an intramuscular injection of hypertonic saline increases variability in knee extensor torque reproduction

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journal contribution
posted on 10.11.2020, 14:19 authored by Samuel Andrew Smith, Dominic Micklewright, Sam WinterSam Winter, Alexis R Mauger
Purpose: The intensity of exercise-induced pain (EIP) reflects the metabolic environment in the exercising muscle, so during endurance exercise this may inform the intelligent regulation of work rate. Conversely, the acute debilitating effects of EIP on motor unit recruitment could impair the estimation of force produced by the muscle and impair judgement of current exercise intensity. This study investigated whether muscle pain that feels like EIP, administered via intramuscular injection of hypertonic saline, interferes with the ability to accurately reproduce torque in a muscle group relevant to locomotive exercise. Methods: On separate days, fourteen participants completed an isometric torque reproduction task of the knee extensors. Participants were required to produce torque at 15 and 20% maximal voluntary torque (MVIT), without visual feedback before (Baseline), during (Pain/No Pain), and after (Recovery) an injection of 0.9% isotonic saline (Control) or 5.8% hypertonic saline (Experimental) into the vastus lateralis of the right leg. Results: An elevated reported intensity of pain, and a significantly increased variance in mean contraction torque at both 15% (P=0.049) and 20% (P=0.002) MVIT was observed in the Experimental compared to the Control condition. Both 15 and 20% target torques were performed at a similar pain intensity in the Experimental condition (15% MVIT, 4.2 ± 1.9; 20% MVIT, 4.5 ± 2.2; P>0.05). Conclusion: These findings demonstrate that the increased muscle pain from the injection of hypertonic saline impeded accurate reproduction of knee extensor torque. These findings have implications for the detrimental impact of EIP on exercise regulation and endurance performance.

History

School

  • Sport, Exercise and Health Sciences

Published in

Journal of Applied Physiology

Volume

130

Issue

1

Pages

57-68

Publisher

American Physiological Society

Version

AM (Accepted Manuscript)

Rights holder

© Journal of Applied Physiology

Publisher statement

This paper was accepted for publication in the journal Journal of Applied Physiology and the definitive published version is available at https://doi.org/10.1152/japplphysiol.00139.2020

Acceptance date

30/10/2020

Publication date

2021-01-14

Copyright date

2021

ISSN

8750-7587

eISSN

1522-1601

Language

en

Depositor

Dr Sam Winter Deposit date: 9 November 2020

Article number

japplphysiol.00139.2020