title: Algogenic substances and metabolic status in work-related Trapezius Myalgia: a multivariate explorative study.
abstract: BACKGROUND
  This study compares the levels of algesic substances between subjects with trapezius myalgia (TM) and healthy controls (CON) and explores the multivariate correlation pattern between these substances, pain, and metabolic status together with relative blood flow changes reported in our previous paper (Eur J Appl Physiol 108:657-669, 2010).
  
  
  METHODS
  43 female workers with (TM) and 19 females without (CON) trapezius myalgia were - using microdialysis - compared for differences in interstitial concentrations of interleukin-6 (IL-6), bradykinin (BKN), serotonin (5-HT), lactate dehydrogenas (LDH), substance P, and N-terminal propeptide of procollagen type I (PINP) in the trapezius muscle at rest and during repetitive/stressful work. These data were also used in multivariate analyses together with previously presented data (Eur J Appl Physiol 108:657-669, 2010): trapezius muscle blood flow, metabolite accumulation, oxygenation, and pain development and sensitivity.
  
  
  RESULTS
  Substance P was significantly elevated in TM (p=0.0068). No significant differences were found in the classical algesic substances (p: 0.432-0.926). The multivariate analysis showed that blood flow related variables, interstitial concentrations of metabolic (pyruvate), and algesic (BKN and K+) substances were important for the discrimination of the subjects to one of the two groups (R2: 0.19-0.31, p<0.05). Pain intensity was positively associated with levels of 5-HT and K+ and negatively associated with oxygenation indicators and IL-6 in TM (R2: 0.24, p<0.05). A negative correlation existed in TM between mechanical pain sensitivity of trapezius and BKN and IL-6 (R2: 0.26-0.39, p<0.05).
  
  
  CONCLUSIONS
  The present study increased understanding alterations in the myalgic muscle. When considering the system-wide aspects, increased concentrations of lactate, pyruvate and K+ and decreased oxygenation characterized TM compared to CON. There are three major possible explanations for this finding: the workers with pain had relatively low severity of myalgia, metabolic alterations preceded detectable alterations in levels of algesics, or peripheral sensitization and other muscle alterations existed in TM. Only SP of the investigated algesic substances was elevated in TM. Several of the algesics were of importance for the levels of pain intensity and mechanical pain sensitivity in TM. These results indicate peripheral contribution to maintenance of central nociceptive and pain mechanisms and may be important to consider when designing treatments.
authors.affiliation: Department of Pain and Rehabilitation Center and Department of Medical and Health Sciences, Linköping University, SE-581 85 Linköping, Sweden. bjorn.gerdle@liu.se.
authors.forename: Björn
authors.initials: B
authors.lastname: Gerdle
authors.forename: Jesper
authors.initials: J
authors.lastname: Kristiansen
authors.forename: Britt
authors.initials: B
authors.lastname: Larsson
authors.forename: Bengt
authors.initials: B
authors.lastname: Saltin
authors.forename: Karen
authors.initials: K
authors.lastname: Søgaard
authors.forename: Gisela
authors.initials: G
authors.lastname: Sjøgaard
mesh_terms: D000328:Adult; D001920:Bradykinin / Q000378:metabolism; D016022:Case-Control Studies; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D017551:Microdialysis; D015999:Multivariate Analysis; D063806:Myalgia / Q000188:drug therapy* / Q000378:metabolism*; D017288:Pain Threshold; D010446:Peptide Fragments / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D011347:Procollagen / Q000378:metabolism; D019289:Pyruvic Acid / Q000378:metabolism; D012039:Regional Blood Flow; D012701:Serotonin / Q000378:metabolism; D013373:Substance P / Q000378:metabolism; D064171:Superficial Back Muscles / Q000098:blood supply / Q000378:metabolism*
chemical_list: D015850:Interleukin-6; D010446:Peptide Fragments; D011347:Procollagen; C047202:procollagen Type I N-terminal peptide; D012701:Serotonin; D013373:Substance P; D018698:Glutamic Acid; D019289:Pyruvic Acid; D007770:L-Lactate Dehydrogenase; D011188:Potassium; D001920:Bradykinin