EMG spectral shift- and 31P-NMR-determined intracellular pH in fatigued human biceps brachii muscle.

We have simultaneously recorded human biceps brachii intracellular pH, estimated by 31P-NMR, and EMG spectral shift, during isometric contraction and recovery in six subjects. This method allows us to concurrently study several components of muscle fatigue. The results show a clear dissociation between the recovery of intracellular pH, force-generating capacity, and the shift to low frequency of the EMG power spectrum induced by fatiguing exercise.