Muscle fiber conduction velocity and contractile properties estimated from surface electrode arrays

Using an array of surface electrodes set 5 mm apart, we estimated the conduction velocities of muscle fibers during submaximal voluntary isometric contraction of human first dorsal interosseous muscle. The conduction velocity obtained by the averaging method ranged from 3.2 to 5.0 m/sec with a mean of 4.2 m/sec. Twitch tensions in the muscle detected during voluntary isometric contractions ranged from 0.31 to 5.97 g with a mean of 2.75 g based on an averaging method triggered by surface myoelectric signals. Thresholds forces of the motor units varied from 120 to 930 g. The rise time of the force developed by isometric adduction ranged from 36.0 to 75.4 msec, with a mean of 55.4 msec. The conduction velocity of the muscle fiber showed a high correlation with the twitch (r = 0.71, n = 50; P < 0.001) and threshold (r = 0.52, n = 50; P < 0.001) forces, but a low one with rise time (r = -0.32, n = 50; P < 0.05). The use of the averaging method with surface electrode arrays, especially for voluntary isometric contractions, shows that motor unit conduction velocity and contractile properties are functionally correlated.