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Harris S.1, Sterling M.2, Farrell S.3, Pedler A.3, Smith A.3
1Griffith University, Allied Health Sciences, Gold Coast, Australia, 2Griffith University, NHMRC Centre for Research Excellence in Recovery Following Road Traffic Injuries, Menzies Health Insitutue; RECOVER Injury Research Centre, Gold Coast, Australia, 3Griffith University, RECOVER Injury Research Centre, Gold Coast, Australia
Background: Endogenous analgesia is often explored through the phenomena of exercise induced hypoalgesia (EIH) and offset analgesia (OffA). Dysfunctional endogenous analgesia has been demonstrated in various chronic pain conditions. Although previous research has indicated the possibility of shared underlying mechanisms underpinning these two phenomena, they have never previously been compared.
Purpose: This study aimed to compare whether the magnitude of percentage change in EIH (at tibialis anterior or the cervical spine) correlated with the magnitude of percentage change in OffA. Additionally, the study aimed to explore whether exercise modulated the effects of OffA.
Methods: EIH and OffA were assessed both before and after a 5 minute isometric quadriceps extension exercise (at 20-25% maximum voluntary contraction), and then once again after a 15 minute rest period. EIH was evaluated using pressure pain thresholds (PPTs) at a local site to exercise (tibialis anterior) and a distal site (cervical spine); these were assessed together with pain ratings of suprathreshold pressure stimuli. The OffA paradigm involved a three-step process (1°C increase in temperature from an individualized baseline = 50%pain rating (T1) to test temperature (T2), and subsequent 1°C decrease (T3)). OffA effect was determined by subtracting the change in respective pain intensity percentages for T1-T2 from those demonstrated between T2-T3. One-way repeated measures analysis of variance was used to evaluate the effect of OffA on PPTs and pain ratings to suprathreshold stimuli.
Results: The study included 36 healthy participants (17 females) with a mean age of 23.6 years (+/- 6.6). There was no correlation demonstrated between EIH (at tibialis anterior or the cervical spine) and OffA (P > .11 for both). OffA was induced (average magnitude of 18%) and was not significantly modulated by exercise (P = .473). EIH effects were only demonstrated locally over tibialis anterior (P = .021), immediately following exercise and at a lower magnitude than expected (11% increase in PPT). These effects were maintained following the 15 minute rest period. Pain ratings to suprathreshold stimuli did not significantly improve with exercise.
Conclusion(s): OffA was robust over time, with exercise failing to modulate its effects, despite demonstration of EIH. Thus, it appears that different mechanisms underlie these phenomena.
Implications: We demonstrated that five minutes of low-intensity isometric exercise can provide non-pharmacological pain modulation in healthy, young adults. This effect did not modulate OffA. Thus, further research is required to understand what modulates OffA, as dysfunction of this phenomena underpins chronicity of various chronic pain disorders.
Funding acknowledgements: Motor Accident Insurance Commission, Australia
National Health and Medical Research Centre, Australia
National Health and Medical Research Centre, Australia
Topic: Pain & pain management
Ethics approval: Griffith University Institutional Human Research Ethics Committee
All authors, affiliations and abstracts have been published as submitted.
