title: Muscle metabolism and acid-base status during exercise in forearm work-related myalgia measured with 31P-MRS.
abstract: In this study, we examined muscle metabolic and acid-base status during incremental wrist extension exercise in the forearm of individuals with work-related myalgia (WRM). Eighteen women employed in full-time occupations involving repetitive forearm labor were recruited in this cross-sectional study. Nine of these women were diagnosed with WRM, while the other nine had no previous WRM history and were used as age-matched controls (Con). Phosphorus-31 magnetic resonance spectroscopy ((31)P-MRS) was used to noninvasively monitor the intracellular concentrations of phosphocreatine ([PCr]) and inorganic phosphate ([P(i)]) as well as intracellular pH (pH(i)) status during exercise in WRM and Con. We observed a 38% decreased work capacity in WRM compared with Con [0.18 W (SD 0.03) vs. 0.28 W (SD 0.10); P = 0.007]. Piecewise linear regression of the incremental exercise data revealed that the onset of a faster decrease in pH(i) (i.e., the pH threshold, pHT) and the onset of a faster increase in log([P(i)]/[PCr]) (i.e., the phosphorylation threshold, PT) occurred at a 14% relatively lower power output in WRM [pHT: 45.2% (SD 5.3) vs. 59.0% (SD 4.6), P < 0.001; PT: 44.8% (SD 4.3) vs. 57.8% (SD 3.1), P < 0.001; % of peak power output, Con vs. WRM, respectively]. Monoexponential modeling of the kinetics of [PCr] and pH(i) recovery following exercise demonstrated a slower (P = 0.005) time constant (tau) for [PCr] in WRM [113 s (SD 25)] vs. Con [77 s (SD 23)] and a slower (P = 0.007) tau for pH(i) in WRM [370 s (SD 178)] vs. Con [179 s (SD 52)]. In conclusion, our results suggest that WRM is associated with an increased reliance on nonoxidative metabolism. Possible mechanisms include a reduction in local muscle blood flow and perfusion, an increased ATP cost of force production, or both.
authors.affiliation: School of Physical and Health Education, Nipissing University, North Bay, ON, Canada. graydonr@nipissingu.ca
authors.forename: Graydon H
authors.initials: GH
authors.lastname: Raymer
authors.forename: Howard J
authors.initials: HJ
authors.lastname: Green
authors.forename: Don A
authors.initials: DA
authors.lastname: Ranney
authors.forename: Greg D
authors.initials: GD
authors.lastname: Marsh
authors.forename: R Terry
authors.initials: RT
authors.lastname: Thompson
mesh_terms: D000136:Acid-Base Equilibrium / Q000502:physiology*; D000328:Adult; D003430:Cross-Sectional Studies; D015444:Exercise / Q000502:physiology*; D017079:Exercise Tolerance / Q000502:physiology; D005260:Female; D005542:Forearm / Q000502:physiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D008875:Middle Aged; D018763:Muscle Fatigue / Q000502:physiology; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000378:metabolism*; D009790:Occupations; D010146:Pain / Q000209:etiology / Q000378:metabolism* / Q000503:physiopathology; D010710:Phosphates / Q000378:metabolism; D010725:Phosphocreatine / Q000378:metabolism; D010766:Phosphorylation
chemical_list: D010710:Phosphates; D010725:Phosphocreatine