The effect of hypertonic saline evoked muscle pain on neurophysiological changes and exercise performance in the contralateral limb

Ryan Norbury,Samuel A Smith,Megan Judge,Mark Burnley,Alexis R Mauger

doi:10.1007/s00221-022-06342-6

Ryan Norbury, Samuel A Smith + Show 3 more

Open Access

https://doi.org/10.1007/s00221-022-06342-6

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Journal: Experimental Brain Research	Publication Date: Mar 14, 2022
Citations: 4	License type: open-access

Affiliation: University of Kent

Abstract

Non-local muscle pain may impair endurance performance through neurophysiological mechanisms, but these are relatively unknown. This study examined the effects of muscle pain on neuromuscular and neurophysiological responses in the contralateral limb. On separate visits, nine participants completed an isometric time to task failure (TTF) using the right knee extensors after intramuscular injection of isotonic saline (CTRL) or hypertonic saline (HYP) into the left vastus lateralis. Measures of neuromuscular fatigue were taken before, during and after the TTF using transcranial magnetic stimulation (TMS) and peripheral nerve stimulation. Mean pain intensity was greater in the left leg in HYP (3.3 ± 1.9) compared to CTRL (0.4 ± 0.7; P < 0.001) which was combined with a reduced TTF by 9.8% in HYP (4.54 ± 0.56 min) compared to CTRL (5.07 ± 0.77 min; P = 0.005). Maximum voluntary force was not different between conditions (all P > 0.05). Voluntary activation was lower in HYP compared to CTRL (P = 0.022). No difference was identified between conditions for doublet amplitude (P > 0.05). Furthermore, no difference in MEP·Mmax−1 or the TMS silent period between conditions was observed (all P > 0.05). Non-local pain impairs endurance performance of the contralateral limb. This impairment in performance is likely due to the faster attainment of the sensory tolerance limit from a greater amount of sensory feedback originating from the non-exercising, but painful, left leg.

Highlights

Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage (Raja et al 2020)
Support for this notion comes from previous work which has found that muscle pain reduces the maximal force generating capacity of the painful muscle (Graven-Nielsen et al 1997, 2002; Khan et al 2011; Norbury et al 2022) and impairs endurance performance (Ciubotariu et al 2004; Smith et al 2020)
Left leg pain did not change over time in CTRL, whereas in hypertonic saline (HYP), pain intensity was increased and greater than CTRL

Summary

Introduction

Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage (Raja et al 2020). The two may be interrelated and exercise-induced pain may at least in part be responsible for the development of fatigue (Mauger 2013) and be determinantal to endurance performance (Mauger et al 2010; Astokorki and Mauger 2017; Stevens et al 2018) Support for this notion comes from previous work which has found that muscle pain reduces the maximal force generating capacity of the painful muscle (Graven-Nielsen et al 1997, 2002; Khan et al 2011; Norbury et al 2022) and impairs endurance performance (Ciubotariu et al 2004; Smith et al 2020).

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