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Introduction: Exercise is the most recommended treatment for chronic low back pain (CLBP) and is effective in reducing pain, but the mechanisms underlying its effects remain poorly understood. Exercise‐induced hypoalgesia (EIH) may play a role and is thought to be driven by central pain modulation mechanisms. However, EIH appears to be disrupted in many chronic pain conditions and its presence in people with CLBP remains unclear. As people suffering from chronic pain often exhibit psychological factors and central sensitization symptoms influencing pain perception, EIH might be associated with these factors. Objective: The aim of this study is to compare the level of EIH between participants with and without CLBP following back and wrist exercises and to assess the associations between EIH, psychological factors, and symptoms of central sensitization (using the central sensitization inventory ‐ CSI) in CLBP. Method: Twenty‐eight participants with CLBP and 23 without pain were recruited. Pressure pain thresholds (PPT) were measured at 4 sites (2 bony sites = capitate, S1|2 muscle sites = wrist flexors, lumbar erector spinae) before and after each of two exercises (wrist flexion and lumbar extension). Exercise‐induced hypoalgesia was defined as percent change in PPT from pre‐ to post‐exercise. Participants with CLBP also completed questionnaires to measure psychological factors (e.g., kinesiophobia, catastrophizing, anxiety, and self‐efficacy) and symptoms of central sensitization (CSI), and correlations with EIH were calculated. Results: After wrist exercise, EIH measured at the muscle sites was lower in the CLBP group compared with the pain‐free group (p = 0.047) but no differences were found at bony sites (p = 0.49). No significant differences for EIH were observed following back exercise at muscle sites (p = 0.14) or at bony sites (p = 0.65). Exercise‐induced hypoalgesia was not correlated with any psychological factors or with the CSI score. Conclusion: The lower EIH following wrist exercises may represent an alteration in pain modulation control in CLBP. However, psychological factors and central sensitization symptoms may not explain the differences observed. [ABSTRACT FROM AUTHOR]

Objective: To determine the absolute and relative intra-rater within-session test-retest reliability of pressure pain threshold (PPT) and mechanical temporal summation of pain (TSP) at the low back and the forearm in healthy participants and to test the influence of the number and sequence of measurements on reliability metrics. Methods: In 24 participants, three PPT and TSP measures were assessed at four sites (2 at the low back, 2 at the forearm) in two blocks of measurements separated by 20 minutes. The standard error of measurement, the minimal detectable change (MDC) and the intraclass correlation coefficient (ICC) were investigated for five different sequences of measurements (e.g. measurement 1, 1–2, 1-2-3). Results: The MDC for the group (MDCgr) for PPT ranged from 28.71 to 50.56 kPa across the sites tested, whereas MDCgr for TSP varied from 0.33 to 0.57 out of 10 (numeric scale). Almost all ICC showed an excellent relative reliability (between 0.80 and 0.97), except when only the first measurement was considered (moderate). Although minimal differences in absolute PPT reliability were present between the different sequences, in general, using only the first measurement increase measurement error. Three TSP measures reduced the measurement error. Discussion: We established that two measurements of PPT and three of TSP reduced the measurement error and demonstrated an excellent relative reliability. Our results could be used in future pain research to confirm the presence of true hypo/hyperalgesia for paradigms such as conditioned pain modulation or exercise-induced hypoalgesia, indicated by a change exceeding the measurement variability. [ABSTRACT FROM AUTHOR]

Objectives: Stretching is an intervention often used in various kinds of rehabilitation protocols and the effects on pain sensitivity has sparsely been investigated, especially when addressing potential effects on pain. The objective is to investigate the immediate effects of an axial and peripheral prolonged stretch on pressure pain sensitivity (PPT) and temporal summation (TS) on local and distal sites in healthy subjects. Methods: Twenty-two healthy volunteers were recruited to participate in this pilot study. Two prolonged stretching protocols were performed: low back and wrist extensors stretches. PPT and pinprick TS were measured pre- and post-intervention at local and remote sites. Repeated measures analysis of variance (ANOVA) was used to examine the effects and significance of the interventions. Results: The low back stretch induced an increase in PPT for both local and remote sites, and the wrist stretch produced a PPT increase only at the local site. TS did not change. Conclusions: Low back stretching induced an increase in PPT at both local and remote sites whereas the wrist stretch only increased PPT locally, suggesting hypoalgesia at these sites. Further studies are needed to confirm the effect and mechanisms using randomised, controlled and parallel study design. Considering that pain sensitivity is different than clinical pain, results are difficult to extrapolate to clinical practice. Future studies testing clinical pain are needed to better understand the clinical implication of these results. [ABSTRACT FROM AUTHOR]

Objective: Exercise may reduce pain sensitivity. This phenomenon called exercise-induced hypoalgesia is observed in different types of exercises and involves the activation of endogenous pain modulation systems. Although the effect of limb exercise on pain sensitivity has often been tested, few studies explored the impact of back exercises that are often used to treat low back pain. The main objective is to measure the effect of back-muscle exercise on pain sensitivity and compare it to the effect of a limb-muscle exercise. Methods: Twenty-three participants who were pain-free performed a 4-min wrist flexion isometric contraction followed by a 4-min low back extension, separated by a 20-min break. Pressure pain thresholds were tested at two low back (S1 spinous process, lumbar erector spinae muscle) and two wrist (capitate bone, wrist flexor muscles) sites before and after each exercise. For each exercise, sites were considered as remote or local in relation to the muscles contracted during the exercise. An independent sample of 11 participants was recruited to confirm the influence of low back extension on pain sensitivity. Results: Wrist exercise induced a larger increase in pain sensitivity than back exercise at the remote site. Only wrist exercise induced a hypoalgesia effect at both the local and the remote sites. Back exercise induced a similar effect in the independent sample. Conclusions: This study showed that back and wrist exercises induced a distinct effect on pain sensitivity in participants who were pain-free. The wrist exercise induced a systemic reduction in pain sensitivity (locally and remotely), whereas the back exercise did not. This differential effect may be present because wrist exercise induced most fatigue compared with the back exercise., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Mailloux, Wideman and Massé-Alarie.)