بررسی اثر آموزش آرام سازی پیشرونده عضلانی بر آستانه رفلکس فلکسیون درد در بزرگسالان جوان و سالم: یک کارآزمایی تصادفی

Although prior studies have demonstrated effects of progressive muscle relaxation (PMR) in reducing self-reported pain, no laboratory studies have examined the effects of PMR on objective indicators of descending modulation of nociception. This randomized controlled study utilized the nociceptive flexion reflex (NFR) to evaluate nociceptive responding among 55 college-age men and women (mean age = 19.4 ± 1.2 years). Participants completed laboratory assessments of NFR threshold and questionnaires evaluating pain and stress. Participants were then randomly assigned to either a 25-min PMR condition or a no-treatment control condition. Following the brief intervention, participants completed a second NFR procedure and self-report questionnaires. Results indicated a significant time by condition interaction for NFR, with participants in the PMR condition experiencing a significant increase in NFR threshold while participants in the no-treatment condition experienced no change in NFR. Ratings of pain did not change during the study, but PMR participants reported decreased stress following the PMR intervention. This is the first study with a randomized no-treatment control group demonstrating the effect of a brief PMR protocol on descending inhibition of nociception. Results support the efficacy of PMR in reducing nociceptive response and provide further evidence of the utility of behavioral pain management strategies.

Prior research has demonstrated beneficial effects of progressive muscle relaxation (PMR) in reducing osteoarthritis pain [10], chronic headache pain [2], and cancer-related pain [22]. The analgesic effect of PMR is thought to result when decreased afferent neural impulses from the skeletal musculature contribute to reduced sympathetic activity [1] and to reduced activity of neuromuscular circuits associated with the experience of pain [15]. PMR also relieves tension in accessory muscles that may contribute to the experience of pain. However, studies have not further evaluated the mechanism by which PMR influences pain, and prior studies have relied primarily on subjective ratings of pain. No studies have evaluated the effect of PMR on an objective indicator of nociceptive responding such as the nociceptive flexion reflex (NFR). The NFR is a polysynaptic spinal reflex used in prior studies examining pain processing [4], [7] and [21]. When elicited by electrical stimulation applied to the foot, the NFR can be recorded via electromyography (EMG) of the hamstring muscles of the upper leg. Stimulation intensities sufficient to activate small diameter (i.e., A-delta) fibers can evoke change in EMG activity corresponding to a nociceptive withdrawal response. The NFR is relatively stable across assessments, with test-retest measurements ranging from 0.55 to 0.81 when recorded up to 24 h apart [9] and [19]. However, thresholds have been found to increase in response to pain medication, TENS, acupuncture, and hypnosis [21]. Further, in a recent study, brief cognitive coping skills training (CST) was associated with significant acute increases in NFR threshold among older adults with osteoarthritis [6]. Because PMR training was a central component of the CST intervention, and because of the efficacy of PMR in reducing subjective pain ratings in prior studies, it was of interest to evaluate the extent to which PMR alone might influence central nociceptive responding. The purpose of the present study was to evaluate the influence of PMR on NFR in a non-clinical population. There were several reasons for pursuing this line of investigation. First, PMR is a shorter intervention than CST and generally less complicated both for instructors to teach and for patients to learn. Second, the prior study of osteoarthritis patients was conducted to evaluate sex differences and did not include a randomized no-treatment control group [6]. To clarify the efficacy of behavioral interventions for influencing central nociceptive responding, it was important to replicate the previous study using a randomized no-treatment control group. This laboratory-based study recruited healthy college-age adults with no history of chronic pain disorder to determine the effect of relaxation training on nociception without introducing the increased variability of pain response that would be likely in a clinical sample. The study evaluated the effect of a single-session relaxation training intervention on NFR threshold, pain ratings, and stress. The single-session format was utilized to facilitate evaluation of acute changes in NFR following the intervention. Based on results of the prior study of patients with OA [6], it was hypothesized that PMR would be associated with increased NFR threshold and reductions in ratings of pain and stress.