The estimation of conduction velocity in human skeletal muscle in situ with surface electrodes.

In the present study new methods were developed for estimation of conduction velocity using surface electrodes. The subjects were 4 healthy male volunteers, aged 23-29 years. EMGs were recorded from m. biceps brachii by several surface electrodes and a fine-wire bipolar electrode during weak isometric contraction with the elbow positioned at 90 degrees. Surface electrodes, 8 mm in diameter, were spaced along the course of muscle fibers at 20 mm intervals, while the bipolar fine-wire electrode was inserted in the middle of the muscle. The EMGs recorded on the magnetic tape were analyzed through a mini-computer system (ATAC-2300). Triggering a signal averager by spike potentials of single motor unit recorded by the inserted electrode, the average contribution of the single motor unit to the surface EMG could be extracted. The conduction velocity in m. biceps brachii determined from the averaged waves of each surface electrode was 4.6 +/- 0.5 m/sec (mean +/- S.D.). The conduction velocity estimated from the cross-correlation analysis between the EMGs of two different surface electrodes agreed well with the value obtained by the averaging technique mentioned above.