Simultaneous measurement of muscle conduction velocity and EMG power spectrum changes during fatigue.

Muscle conduction velocity and mean frequency of the electromyogram (EMG) spectrum were measured simultaneously in the biceps brachii muscles of nine healthy subjects during sustained isometric contraction. Recordings were made at 60% and 70% of the maximum voluntary contraction. In all subjects, both conduction velocity and mean frequency decreased during the time period of the fatiguing contractions. Also, the muscle conduction velocity was found to vary linearly with the mean frequency. This demonstrates that the EMG spectral shifts observed during muscle fatigue are due to slowing of the conduction velocity.