Associations Between Activity And Exercise-Induced Changes In Endocannabinoids In Adults With Chronic Low Back Pain

Exercise-induced hypoalgesia (EIH) is a decrease in pain post-exercise, which can be moderated by activity level and may be related to changes in endocannabinoids (eCBs). Individuals with chronic low back pain (CLBP) may not experience EIH. PURPOSE The purpose of this study was to explore associations between objective assessments of activity (i.e., sedentary time, steps, and moderate-to-vigorous physical activity [MVPA]) and changes in eCBs (i.e., 2AG and AEA) and pain in individuals with CLBP. METHODS 40 participants with CLBP and 20 age/sex matched-pain free adults (PF) wore an activPAL3 accelerometer for 7 days. Participants then completed the McGill Pain Questionnaire (MPQ) and had their blood drawn prior to and following a 30-minute moderate intensity exercise session on a cycle ergometer. From the activPAL, objective assessments of activity were obtained. Levels of circulating eCBs were quantified in serum. Total scores from the MPQ were used to assess perceived pain. To assess exercise response, change scores for AEA, 2AG, and pain were used. Pearson correlations explored associations between sitting time, steps, and MVPA, with changes in AEA, 2AG, and MPQ for both PF and CLBP. RESULTS Correlations between activity level and MPQ scores were non-significant for CLBP (r = -0.07 to 0.02, p > 0.05) and PF (r = -0.07 to 0.13, p > 0.05). Correlations between activity level and eCB exercise response were non-significant for those with CBLP (r = -0.17 to 0.14, p > 0.05). In PF, there were strong and moderate positive correlations between MVPA and changes in 2AG (r = 0.66) and AEA (r = 0.31), respectively, a moderate positive correlation between steps and changes in 2AG (r = 0.44), and a strong negative correlation between sitting time and changes in 2AG (r = -0.56). CONCLUSION Activity levels of those with CLBP did not appear related to eCB changes with exercise. For PF individuals, higher activity levels and lower sitting time were significantly correlated with the exercise-induced changes of eCBs (2AG and AEA). This shows that eCB release in response to exercise may be influenced by physical activity and sitting time in the general population (PF individuals), but not in those with CLBP. Further understanding of how pain may interfere with natural eCB activity in response to exercise in chronic pain populations appears warranted.