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This Article Full Text Full Text (PDF) All Versions of this Article: 106/4/1198    most recent 90925.2008v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Raymer, G. H. Articles by Thompson, R. T. Search for Related Content PubMed PubMed Citation Articles by Raymer, G. H. Articles by Thompson, R. T.

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

¹School of Physical and Health Education, Nipissing University, North Bay; and ²Department of Kinesiology, Faculty of Applied Health Science, University of Waterloo, and ³Department of Medical Biophysics, Schulich School of Medicine and Dentistry, University of Western Ontario, ⁴Imaging Division, Lawson Health Research Institute, St. Joseph's Health Care, and ⁵School of Kinesiology, Faculty of Health Sciences, University of Western Ontario, London, Ontario Canada

Submitted 18 July 2008 ; accepted in final form 17 December 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 (³¹P-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 () for [PCr] in WRM [113 s (SD 25)] vs. Con [77 s (SD 23)] and a slower (P = 0.007) 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.

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