Physical Activity and Chronic Pain: From Cells to Systems and Beyond
This workshop concentrated on the role of physical activity and exercise in the prevention and treatment of chronic pain, presented by Dr Sluka, Dr Bement and Dr Rovner. The audience was taken on a journey from basic science studies and predictive behavioral factors to translational application in the form of recommendations for exercise prescription in specific populations.
In her talk, ‘PHYSICAL ACTIVITY PREVENTS CHRONIC PAIN: UNDERLYING MECHANISMS’, Dr Sluka (from the University of Iowa) presented her animal research that focused on the role of exercise in the transition from acute to chronic pain, emphasising neuroplastic changes in the peripheral and central nervous systems [1]. This research tested the hypothesis that exercise activates central inhibitory pathways that produce an opioid-mediated analgesia. Different forms of pain were induced, including: (1) chronic muscle pain, induced by repeated intramuscular injection of pH 4.0 saline, and (2) acute muscle inflammation, induced by carrageenan injection. Prior to the pain induction, mice were allowed access to exercise wheels for 5 days or 8 weeks and compared with sedentary mice without running wheels in their cages. In the chronic muscle pain model, mice that exercised for 8 weeks did not develop hyperalgesia compared with the mice in the short-term exercise (5 days) or sedentary groups. The protective effect of exercise was temporary; hyperalgesia returned 13 days after removal of the running wheel. Eight weeks of exercise did not prevent hyperalgesia in the acute pain model. Protective pain still occurs in response to an acute injury. Immunohistochemical analyses demonstrated that regular physical activity prevented increased NMDA receptor activity in the rostral ventromedial medulla (RVM), indicating a decrease in neuronal excitability which normally occurs in sedentary animals in response to induction of chronic muscle pain. Dr Sluka concluded that these data suggest that regular exercise reduces pain by activation of opioid receptors in descending inhibitory pathways in the central nervous system. She further proposed that regular exercise could prevent the transition from acute to chronic pain through the release of regulatory macrophages and increased levels of IL-10, an anti-inflammatory cytokine which can reduce nociceptor sensitisation [2].
Dr Rovner continued with her presentation, ‘BEYOND: BEHAVIORAL CHANGES: ASSESSMENT, PREDICTION AND REHABILITATION PROGRAMS’ on how different assessment strategies can be used to predict outcomes in rehabilitation programmes. Dr Rovner proposed that might be possible to identify which patients can benefit from programmes such as Acceptance and Commitment Therapy (ACT) by identifying clinically relevant subgroups. ACT promotes the acceptance of pain rather than focusing on symptoms. ACT consists of awareness and non-judgmental acceptance of all experiences (positive and negative), identification of life values and appropriate action to support those values [3]. It warrants assessment procedures that can predict behavioural changes and improve the selection of patients for appropriate rehabilitation programmes. Dr Rovner emphasised that, among all instruments included in the Swedish National Registry for Pain Rehabilitation, pain acceptance emerged as the most useful indicator for rehabilitation. Pain acceptance could also distinguish differences between male and female participants before rehabilitation, suggesting that it could have clinical utility for treatment matching and development of sex-specific treatment approaches. Acceptance may be a useful assessment in the triage of patients into ACT-based rehabilitation programmes [4]. The short form Chronic Pain Acceptance Questionnaire is suitable for this purpose as it shows good psychometric properties and sensitivity to rehabilitation changes within those programmes [5].
Dr Bement closed off the session with her presentation, ‘ROLE OF EXERCISE IN THE MANAGEMENT OF PAIN ACROSS THE LIFESPAN’. Evidence suggests that isometric, aerobic and dynamic resistance training may have acute hypoalgesic effects in healthy people, but effect sizes vary greatly, not the least due to differences in exercise intensities. Studies on dose effects of isometric contractions showed that effects are greatest after a low-intensity submaximal contraction sustained to failure [6]. Decreases in pain with isometric contractions were not localised to the working muscle and were considered to be systemic. Studies on people with chronic pain have also yielded inconsistent findings in terms of magnitude and direction of effect sizes, which might be related to different conditions and exercise intensities or may suggest that exercise does not have a reliable effect [7]. In women with fibromyalgia, isometric contractions can lead to a variable pain response (increase, decrease, no change in pain). Significant predictors of the experimental pain response after the isometric contractions included age, baseline experimental pain and change in fibromyalgia pain intensity [8]. Lemley et al. (2014) showed that conditioned pain modulation (the inhibition of pain by pain), was attenuated in older adults, and that adults with greater conditioned pain modulation were more likely to report greater exercise-induced analgesia. However, the optimal dose of exercise for producing hypoalgesia in specific populations and conditions has yet to be determined.
Dr Rovner summed up the session with,
“We don’t know which exercise programmes are best, but almost everything we try is getting them moving. It is important that the programmes contain education to reconceptualise pain as protective, and that the participants have a strong message that they are not broken.”
About Markus Hübscher
Markus Hübscher is a research officer at Neuroscience Research Australia and a member of the pain research group headed by Lorimer Moseley. Before coming to Australia in 2011 to do his postdoc in the Faculty of Health Sciences, Sydney University, he worked for several years as a lecturer and researcher in the Department of Sports Medicine, University of Frankfurt, Germany, where he received his Master’s and Ph.D. degrees in Sports Science.
The overarching focus of his research is the prevention and management of musculoskeletal conditions such as spinal pain and sports injuries. He is especially interested in the relationship between pain, biomechanics and sensory-motor control. The role of physical activity and exercise to enhance, maintain or restore performance and musculoskeletal health is another important area of his research.
About Sandy Hilton
Sandy is a physical therapist with a private practice in Lincoln Park – Chicago, USA. She is incurably curious about how much of the latest pain research can be applied in the clinical treatment of people suffering from persistent pelvic pain. In her spare time she hits the stand-up comedy open mics in Chicago, surprising audiences with tidbits about sex, pain and pelvic health.
References
[1] Sluka KA, O’Donnell JM, Danielson J, & Rasmussen LA (2013). Regular physical activity prevents development of chronic pain and activation of central neurons. J Appl Physiol, 114 (6), 725-33 PMID: 23271699
[2] Leung, A., Kolker, S., Gregory, N., Allen, L., & Sluka, K. (2013). Regular physical activity results in a phenotypic switch in resident macrophages in muscle and prevents development of chronic pain through release of IL-10 Pain, 14 (4) DOI: 10.1016/j.jpain.2013.01.496
[3] Hayes S, Hogan M, Dowd H, Doherty E, O’Higgins S, Nic Gabhainn S, MacNeela P, Murphy AW, Kropmans T, O’Neill C, Newell J, & McGuire BE (2014). Comparing the clinical-effectiveness and cost-effectiveness of an internet-delivered Acceptance and Commitment Therapy (ACT) intervention with a waiting list control among adults with chronic pain: study protocol for a randomised controlled trial. BMJ open, 4 (7) PMID: 24993763
[4] Rovner G. Indicators for Behavioral Pain Rehabilitation Impact and predictive value on assessment, patient-selection, treatment and outcome. PhD thesis, University of Gothenburg, Sweden, 2014.
[5] Rovner, G., Ãrestedt, K., Gerdle, B., Börsbo, B., & McCracken, L. (2014). Psychometric properties of the 8-item Chronic Pain Acceptance Questionnaire (CPAQ-8) in a Swedish Chronic pain cohort J Rehabil Med., 46 (1), 73-80 DOI: 10.2340/16501977-1227
[6] Hoeger Bement MK, Dicapo J, Rasiarmos R, & Hunter SK (2008). Dose response of isometric contractions on pain perception in healthy adults. Med Sci Sports Exerc., 40 (11), 1880-9 PMID: 18845975
[7] Naugle KM, Fillingim RB, & Riley JL 3rd (2012). A meta-analytic review of the hypoalgesic effects of exercise. J Pain, 13 (12), 1139-50 PMID: 23141188
[8] Hoeger Bement MK, Weyer A, Hartley S, Drewek B, Harkins AL, & Hunter SK (2011). Pain perception after isometric exercise in women with fibromyalgia. Arch Phys Med Rehabil., 92 (1), 89-95 PMID: 21187210
[9] Lemley KJ, Hunter SK, & Hoeger Bement MK (2014). Conditioned Pain Modulation Predicts Exercise-Induced Hypoalgesia in Healthy Adults. Med Sci Sports Exerc. PMID: 24870571 [Epub ahead of print]