Inventory of personal factors influencing conditioned pain modulation in healthy people: a systematic literature review

Background: Conditioned pain modulation (CPM) is believed to play an important role in the development and exacerbation of chronic pain, because dysfunction of CPM is associated with a shift in balance between pain facilitation and pain inhibition. In many patients with central sensitization, CPM is less efficacious. Besides that, efficacy of CPM is highly variable in healthy people. Consequently, it seems that several individual variables may influence CPM. A systematic review examining personal factors influencing CPM was conducted. Methods: This systematic review follows the PRISMA guidelines. Pubmed and Web of Science were searched using different synonyms of CPM. Full-text clinical reports addressing the influence of personal factors on CPM in healthy adults were included. Checklists for RCTs and case-control studies provided by the Dutch Institute for Healthcare Improvement (CBO) and the Dutch Cochrane Centre were utilized to assess methodological quality. Levels of evidence and strength of conclusion were assigned using the CBO guidelines. Results: Forty-six articles were identified that reported the influence of personal factors on CPM. Quality assessment revealed 10 studies with a methodological quality less than 50% wherefore they were excluded (21.8%), resulting in a general total methodological quality score of 72.5%. Overall younger adult age, male gender, ovulatory phase, positive expectations, attention to the conditioning stimulus, and carrier of the 5-HTTLPR long allele result in better CPM. Conclusion: It is advised for future studies to take these factors into account. Further research regarding the influence of oral contraceptives, catastrophizing, information about conditioning stimulation, distraction, physical activity, and genetics on CPM magnitude is required

An overview of offset analgesia and the comparison with conditioned pain modulation : a systematic literature review

Background: Offset analgesia (OA) is an increasingly described phenomenon to measure endogenous pain inhibition, in which a greater decrease in pain intensity is experienced than would be predicted by the decrease in painful stimulation. The temporal filtering in this OA phenomenon differs from the spatial filtering in the commonly described conditioned pain modulation (CPM). Yet, the knowledge on the efficacy of OA in chronic pain patients is scarce, compared to CPM efficacy. Objective: This systematic review has been conducted to provide an overview of the current knowledge regarding OA, and to compare it to CPM. Study Design: A systematic review of research studies that investigated the application or mechanisms of OA. Setting: The present study took place at Ghent University and the University of Antwerp. Methods: This systematic review follows the PRISMA guidelines. The electronic databases Pubmed and Web of Science were searched in January 2015. Full text clinical reports addressing OA were included. The checklists for randomized controlled trials, case-control studies, and cohort-studies provided by the Dutch Institute for Healthcare Improvement and the Dutch Cochrane Centre were used to assess methodological quality. The articles received a level of evidence A1, A2, B, C, or D, based on study design and risk of bias. These levels were used to determine the strength of conclusion (level 1 to 4). Results: Seventeen articles met the inclusion criteria. Sixteen studies used quantitative sensory testing to provoke OA; however, differences in protocols are present. OA can function as a non-opioid mediated assessment tool for endogenous pain inhibition, and activates brain regions such as periaqueductal gray (PAG), dorsolateral prefontral cortex, insula, medulla, pons and cerebellum, indicating strong brain derived pain modulation. The primary somatosensory cortex is, conversely, less activated during OA. OA is decreased in neuropathic patients. Nonetheless, evidence for the influence of individual factors on OA is limited. OA and CPM seem to rely on different mechanisms. Limitations: Search strategy was taken wide, wherefore a large variety of research perspectives were included. Conclusions: This systematic review displays OA as a temporal filtering mechanisms that is more brain-derived compared to the spatial assessment method CPM. There is strong evidence for reduced OA in neuropathic patients, however, evidence regarding OA in (sub) acute and central sensitization patients, and the influence of personal factors on OA is currently scarce and needs further investigation

Foci of segmentally contracted sarcomeres in trapezius muscle biopsy specimens in myalgic and nonmyalgic human subjects : preliminary results

Objective The myofascial trigger point hypothesis postulates that there are small foci of contracted sarcomeres in resting skeletal muscle. Only one example, in canine muscle, has been published previously. This study evaluated human muscle biopsies for foci of contracted sarcomeres. Setting The Departments of Rehabilitation Sciences and Physiotherapy at Ghent University, Ghent, Belgium. Subjects Biopsies from 28 women with or without trapezius myalgia were evaluated, 14 in each group. Methods Muscle biopsies were obtained from regions of taut bands in the trapezius muscle and processed for light and electron microscopy and for histochemical analysis. Examination of the biopsies was blinded as to group. Results A small number of foci of segmentally contracted sarcomeres were identified. One fusiform segmental locus involved the entire muscle fiber in tissue from a myalgic subject. Several transition zones from normal to contracted sarcomeres were found in both myalgic and nonmyalgic subjects. The distance between Z-lines in contracted sarcomeres was about 25–45% of the same distance in normal sarcomeres. Z-lines were disrupted and smeared in the contracted sarcomeres. Conclusions A small number of foci of segmentally contracted sarcomeres were found in relaxed trapezius muscle in human subjects, a confirmation of the only other example of spontaneous segmental contraction of sarcomeres (in a canine muscle specimen), consistent with the hypothesis of trigger point formation and with the presence of trigger point end plate noise

Association between insulin resistance, lean mass and muscle torque/force in proximal versus distal body parts in healthy young men

Objectives:The purpose of this study was to investigate whether there is already an association of insulin resistance (IR) with muscle mass and –force/torque in an adult population and whether this relationship is the same in distal and proximal body parts. Methods: 358 Healthy young men were divided into a more insulin sensitive (MIS) (n=89) and a less insulin sensitive (LIS) group (n=89), respectively using lower and upper quartiles of HOMA-IR index (Homeostasis Model Assessment of IR). Muscle force/torque and lean mass, were compared between the two groups. Results: LIS subjects had higher absolute thigh lean mass, but not higher thigh muscle torque, resulting in a lower torque per kg muscle. In upper arm, lean mass was higher in LIS subjects, but also absolute muscle torque resulted higher. For handgrip force, the LIS and MIS group had similar results, despite a trend towards higher forearm lean mass in LIS subjects. Lean mass % of total lean mass is lower in LIS subjects in more distal body parts. Conclusions:Already in a young healthy population, IR seems to be associated with lower force/torque per muscle mass and lower lean mass % of total lean mass predominantly in more distal body parts

Impact of exercise-nutritional state interactions in patients with type 2 diabetes

Introduction This study examines the role of nutritional status during exercise training in patients with type 2 diabetes mellitus by investigating the effect of endurance-type exercise training in the fasted versus the fed state on clinical outcome measures, glycemic control, and skeletal muscle characteristics in male type 2 diabetes patients. Methods Twenty-five male patients (glycated hemoglobin (HbA1c), 57 ± 3 mmol·mol−1 (7.4% ± 0.3%)) participated in a randomized 12-wk supervised endurance-type exercise intervention, with exercise being performed in an overnight-fasted state (n = 13) or after consuming breakfast (n = 12). Patients were evaluated for glycemic control, blood lipid profiles, body composition and physical fitness, and skeletal muscle gene expression. Results Exercise training was well tolerated without any incident of hypoglycemia. Exercise training significantly decreased whole-body fat mass (−1.6 kg) and increased high-density lipoprotein concentrations (+2 mg·dL−1), physical fitness (+1.7 mL·min−1·kg−1), and fat oxidation during exercise in both groups (PTIME 0.05). HbA1c concentrations significantly decreased after exercise training (PTIME < 0.001), with a significant greater reduction after consuming breakfast (−0.30% ± 0.06%) compared with fasted state (−0.08% ± 0.06%; mean difference, 0.21%; PTIME × GROUP = 0.016). No interaction effects were observed for skeletal muscle genes related to lipid metabolism or oxidative capacity. Conclusions Endurance-type exercise training in the fasted or fed state do not differ in their efficacy to reduce fat mass, increase fat oxidation capacity, and increase cardiorespiratory fitness and high-density lipoprotein concentrations or their risk of hypoglycemia in male patients with type 2 diabetes. HbA1c seems to be improved more with exercise performed in the postprandial compared with the postabsorptive state