Impulse conduction velocities in human biceps brachii muscles.

Measurements of impulse conduction velocity were made in biceps brachii muscle fibers of male or female controls and of male body-builders. The technique involved exciting bundles of fibers with stimulating electrodes applied over the surface of the muscle, and recording compound action potentials with three small surface electrodes spaced 3 cm apart. By measuring latencies to the onsets and to the peaks of the negative deflections, it was possible to estimate conduction velocities in the fastest-conducting (FC) and intermediate-conducting (IC) fibers; the observed values ranged from 2.8 to 5.5 m X s-1 in normal men and women. The mean conduction velocity for FC fibers was significantly higher in body-builders than in normal men and women; the mean IC value was significantly lower in women. In all three groups of subjects a decrease in conduction velocity could be demonstrated for FC fibers at the end of 1 min of maximal isometric contraction. In the body-builders, and probably in the other two groups of subjects, the FC fibers are considered to correspond to type II muscle fibers.