Modulation Differences of Exercise-Induced Hypoalgesia in Subgroups of Healthy Subjects Following an Exercise Intervention

Modulation Differences of Exercise-Induced Hypoalgesia in Subgroups of Healthy Subjects Following an Exercise Intervention Poster topic: Assessment, Diagnosis and Measurement in Pain Simon Hansen1; Rasmus Christiansen Dalgaard1; Pernille Schlosser Mikkelsen1; Mathias Brandhøj Sørensen1; Kristian Kjær Petersen1,2 1SMI, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark. 2Center for Neuroplasticity and Pain, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark. Background and aims: Physical activity (exercise) is recommended to promote and maintain health and as treatment for more than 25 diseases and pain conditions (1). Exercise-induced hypoalgesia (EIH), a measure of descending pain inhibitory control, has been found lower in physically inactive individuals compared to physically active people (2,3) indicating EIH subgroup differences and that exercise or an active lifestyle (enhanced physical capacity) may improve EIH. However, the impact of extensive exercise on EIH has not been investigated in healthy subjects. The aims of this study was to investigate 1) the modulation of EIH following basis military training (MT) and 2) the association between change in physical capacity assessed using the Endurance 20-m Shuttle Run Fitness Test (20MSR) and change in EIH. Methods: In 38 healthy new recruits (mean ± SEM, age 20.5 ± 0.3 years, body mass index 22.5 ± 0.3 kg/m2, 63.2% males), EIH was assessed as absolute change in pressure pain threshold (PPT) at the dominant m. quadriceps femoris (local EIH) and the contralateral m. deltoideus (remote EIH) after 3-minute isometric wall squat within the first week and after the seventh week of MT. Furthermore, temporal summation of pain (TSP) and Knee injury and Osteoarthritis Outcome Score (KOOS) were assessed. A hypoalgesic (EIH>0.0 kPa) and a hyperalgesic (EIH≤0.0 kPa) subgroup was defined based on baseline local EIH. The study was approved by the local ethical committee (N-20170070). All subjects gave oral and written informed consent prior to the experiments. Clinicaltrials.gov registration number: NCT03718663. Results: Following MT, increased remote EIH (P=0.008), PPTs (P<0.003) and 20MSR (P<0.001) were found, with no changes in TSP and KOOS (P>0.05). Ten subjects (26%) had a hyperalgesic local EIH-response at baseline. In the subgroup analysis, the hyperalgesic subgroup showed signs of hypoalgesic local and remote EIH-responses to the wall squat test following MT (P=0.010), while the hypoalgesic subgroup EIH-responses was unchanged comparing baseline to follow-up (P>0.05). Finally, in the pooled data, an association between change in 20MRS and change in remote EIH was found (r=0.369; P=0.023). Conclusions: MT increased EIH, especially in subjects who demonstrated a baseline hyperalgesic response. Improvement in physical capacity was associated with a hypoalgesic response to the wall squat test, indicating that improvement in physical performance may improve central pain mechanisms. Conflicts of interest: none Financial support: Kristian Kjær Petersen is supported by The Aalborg University Talent Management Program (j.no. 771126). Center for Neuroplasticity and Pain (CNAP) is supported by the Danish National Research Foundation (DNRF121). 1. Pedersen BK, Saltin B. Exercise as medicine - evidence for prescribing exercise as therapy in 26 different chronic diseases. Scand J Med Sci Sports [Internet]. 2015 Dec;25 Suppl 3:1–72. Available from: http://www.ncbi.nlm.nih.gov/pubmed/26606383 2. Umeda M, Kempka LE, Greenlee BT, Weatherby AC. A smaller magnitude of exercise-induced hypoalgesia in African Americans compared to non-Hispanic Whites: A potential influence of physical activity. Biol Psychol [Internet]. 2016 Jan;113:46–51. Available from: http://www.ncbi.nlm.nih.gov/pubmed/26607443 3. Ohlman T, Miller L, Naugle KE, Naugle KM. Physical Activity Levels Predict Exercise-induced Hypoalgesia in Older Adults. Med Sci Sports Exerc [Internet]. 2018 Oct;50(10):2101–9. Available from: http://www.ncbi.nlm.nih.gov/pubmed/29757826