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, 15 (12), 1294-1304

Mechanisms of Exercise-Induced Hypoalgesia

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Mechanisms of Exercise-Induced Hypoalgesia

Kelli F Koltyn et al. J Pain.

Abstract

The purpose of this study was to examine opioid and endocannabinoid mechanisms of exercise-induced hypoalgesia (EIH). Fifty-eight men and women (mean age = 21 years) completed 3 sessions. During the first session, participants were familiarized with the temporal summation of heat pain and pressure pain protocols. In the exercise sessions, following double-blind administration of either an opioid antagonist (50 mg naltrexone) or placebo, participants rated the intensity of heat pulses and indicated their pressure pain thresholds and pressure pain ratings before and after 3 minutes of submaximal isometric exercise. Blood was drawn before and after exercise. Results indicated that circulating concentrations of 2 endocannabinoids, N-arachidonylethanolamine and 2-arachidonoylglycerol, as well as related lipids oleoylethanolamide, palmitoylethanolamide, N-docosahexaenoylethanolamine, and 2-oleoylglycerol, increased significantly (P < .05) following exercise. Pressure pain thresholds increased significantly (P < .05), whereas pressure pain ratings decreased significantly (P < .05) following exercise. Also, temporal summation ratings were significantly lower (P < .05) following exercise. These changes in pain responses did not differ between the placebo and naltrexone conditions (P > .05). A significant association was found between EIH and docosahexaenoylethanolamine. These results suggest involvement of a nonopioid mechanism in EIH following isometric exercise.

Perspective: Currently, the mechanisms responsible for EIH are unknown. This study provides support for a potential endocannabinoid mechanism of EIH following isometric exercise.

Conflict of interest statement

Disclosures: There are no conflicts of interest with this study, none of the authors have anything to disclose. All authors participated in the conduct of this study.

Figures

Figure 1
Figure 1
Schematic of the Experimental Procedures, BP = blood pressure; min = minutes
Figure 2
Figure 2
Means and standard errors for pressure pain thresholds pre and post exercise in the placebo and naltrexone conditions; *indicates a significant increase (p < 0.05) post exercise in both conditions. Note: assessments were taken twice before exercise, i.e., baseline and pre-exercise but have been combined in the figure because they were not significantly different.
Figure 3
Figure 3
Means and standard errors for pressure pain ratings pre and post exercise in the placebo and naltrexone conditions; *indicates a significant increase in pain ratings (p < 0.05) over the two minutes; +indicates a significant decrease (p < 0.05) in pain ratings at that time from pre to post exercise. Note: assessments were taken twice before exercise, i.e., baseline and pre-exercise but have been combined in the figure because they were not significantly different.
Figure 4
Figure 4
Means and standard errors for temporal summation ratings pre and post exercise in the placebo and naltrexone conditions; *indicates a significant decrease (p < 0.05) in pain ratings at that pulse post exercise. Note: assessments were taken twice before exercise, i.e., baseline and pre-exercise but have been combined in the figure because they were not significantly different.
Figure 5
Figure 5
Means and standard errors for biogenic lipids at baseline, pre, and post exercise in the placebo condition only; n = 58; *indicates a significant increase (p < 0.05) in concentration from baseline to post exercise

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