Muscle metabolism and acid-base status during exercise in forearm work-related myalgia measured with ^sup 31^P-MRS

• Published in: Journal of applied physiology (1985) Vol. 106; no. 4; p. 1198
• Main Authors: Raymer, Graydon H, Green, Howard J, Ranney, Don A, Marsh, Greg D, Thompson, R Terry
• Format: Journal Article
• Language: English
• Published: Bethesda American Physiological Society 01.04.2009
• Subjects: Adenosine triphosphatase; Exercise; Metabolism; Muscular system; Phosphorus; Spectrum analysis; Women
• ISSN: 8750-7587; 1522-1601

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 (...-MRS) was used to noninvasively monitor the intracellular concentrations of phosphocreatine ([PCr]) and inorganic phosphate ([P...]) as well as intracellular pH (pH...) 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 pHi (i.e., the pH threshold, pHT) and the onset of a faster increase in log([P...]/[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 pHi recovery following exercise demonstrated a slower (P = 0.005) time constant (...) for [PCr] in WRM [113 s (SD 25)] vs. Con [77 s (SD 23)] and a slower (P = 0.007) ... for pH... 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. (ProQuest: ... denotes formulae/symbols omitted.)