COMBINED ELECTROMYOGRAPHY-P-31-MAGNETIC RESONANCE SPECTROSCOPY STUDY OF HUMAN MUSCLE FATIGUE DURING STATIC CONTRACTION

Metabolic changes measured by P-31-magnetic resonance spectroscopy and surface electromyograms were simultaneously recorded during isometric contraction of forearm flexor muscles sustained at 60% of maximal for ce until exhaustion. Throughout the fatigue trial, energy in the low-f requency (L) band continuously increased whereas energy in the high-fr equency (H) band first increased and fell only prior to exhaustion. PC r content decreased linearly. Intracellular pH (pi-ii) transiently inc reased during the first 22 s of trial, The triggering of acidosis was associated with critical PCr values (35-70% of initial content) and de creased electromyogram (EMG) energy in the H band. Linear relationship s were only found between energy in the L band, pHi, and PCr content. The interindividual variability of metabolic and EMG changes was high despite standardized conditions of contraction, Maximal PCr consumptio n was correlated with the maximal pHi decrease measured at the end of the trial. Overall, there was no correlation between H/L EMG ratio and changes in muscle metabolism. (C) 1996 John Wiley & Sons, Inc.