Hypoalgesia after exercises with painful vs. non-painful muscles in healthy subjects - a randomized cross-over study

Simon Hansen; Kristian Kjær Petersen; Emilie Sloth; Line Appelon Manum; Anita Kjær McDonald; Per Grünwald Andersen; Henrik Bjarke Vaegter

doi:10.1515/sjpain-2021-0161

Hypoalgesia after exercises with painful vs. non-painful muscles in healthy subjects - a randomized cross-over study

Scand J Pain. 2021 Dec 27;22(3):614-621. doi: 10.1515/sjpain-2021-0161. Print 2022 Jul 26.

Authors

Simon Hansen¹, Kristian Kjær Petersen^{1

2}, Emilie Sloth³, Line Appelon Manum³, Anita Kjær McDonald³, Per Grünwald Andersen⁴, Henrik Bjarke Vaegter^{4

5}

Affiliations

¹ Department of Health Science and Technology, SMI, Faculty of Medicine, Aalborg University, Aalborg, Denmark.
² Department of Health Science and Technology, Center for Neuroplasticity and Pain, Faculty of Medicine, Aalborg University, Aalborg, Denmark.
³ School of Physiotherapy, University College Lillebaelt, Odense, Denmark.
⁴ Pain Research Group, Pain Center, Odense University Hospital, Odense, Denmark.
⁵ Department of Clinical Research, Faculty of Health Sciences, University of Southern Denmark, Odense, Denmark.

PMID: 34958721
DOI: 10.1515/sjpain-2021-0161

Abstract

Objectives: Exercise-induced hypoalgesia (EIH) is a decrease in the pain sensitivity after exercise. Individuals with chronic pain show less EIH after one exercise session compared with pain-free individuals possibly due to pain in exercising muscles. The primary aim of this randomized controlled cross-over study was to compare the EIH response at the exercising thigh muscle following exercises performed with painful vs. non-painful muscles. Secondary aims were to explore if a reduced EIH response was confined to the painful muscle, and whether the muscle pain intensity and the EIH responses were negatively associated.

Methods: In two sessions, 34 pain-free participants received a painful (hypertonic saline, 5.8%) injection and a control (isotonic saline, 0.9%) injection in the right thigh muscle before performing a 3 min isometric wall squat exercise. Pressure pain thresholds (PPTs) were assessed at both thighs and the left neck/shoulder at baseline, after injections and after exercise. Pain intensities in the thighs were rated on numerical rating scales (NRS: 0-10).

Results: Hypertonic saline induced moderate thigh pain at rest (NRS: 4.6 ± 2.1) compared to the control injection (NRS: 0.3 ± 0.4; p<0.001). EIH at the thighs and neck/shoulder were not different between sessions (Injected thigh: 0 kPa; 95% CI: -51 to 52; Contralateral thigh: -6 kPa; 95% CI: -42 to 30; neck/shoulder: 19 kPa; 95% CI: -6 to 44). No significant associations between pain intensity ratings immediately after the Painful injection and EIH responses at any assessment sites were found (right thigh: β=0.08, 95% CI: -12.95 to 20.64, p=0.64, left thigh: β=-0.33, 95% CI: -27.86 to 0.44, p=0.06; neck/shoulder: β=-0.18, 95% CI: -15.11 to 4.96, p=0.31).

Conclusions: Pain in the area of an exercising muscle did not reduce local or systemic EIH responses.

Trial registration number: NCT04354948.

Keywords: exercise; exercise-induced hypoalgesia; experimental pain; isometric exercise; pain modulation; saline injection.

Publication types

Randomized Controlled Trial
Research Support, Non-U.S. Gov't

MeSH terms

Cross-Over Studies
Healthy Volunteers
Humans
Hypesthesia*
Isometric Contraction* / physiology
Muscle, Skeletal
Myalgia

Associated data

ClinicalTrials.gov/NCT04354948