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

作者：Raymer Graydon H^*; Green Howard J; Ranney Don A; Marsh Greg D; Thompson R Terry

来源：Journal of Applied Physiology, 2009, 106(4): 1198-1206.

DOI：10.1152/japplphysiol.90925.2008

• phosphorus magnetic resonance spectroscopy
• extensor carpi radialis brevis
• wrist extension
• intracellular pH
• phosphocreatine
• intracellular threshold
• recovery
• repetitive strain injury

Raymer GH, Green HJ, Ranney DA, Marsh GD, Thompson RT. Muscle metabolism and acid-base status during exercise in forearm work-related myalgia measured with P-31-MRS. J Appl Physiol 106: 1198-1206, 2009. First published December 26, 2008; doi:10.1152/japplphysiol.90925.2008.-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 (P-31-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.

• 出版日期2009-4