Muscle sounds from evoked twitches in the hand

Skeletal muscle emits acoustic signals during voluntary contraction and during twitches produced by electric stimulation of peripheral nerves. Supramaximal, percutaneous electric stimulation was applied to the median or ulnar nerve, while electric and sound signals were recorded from the abductor pollicis brevis or abductor digiti minimi muscles, respectively, in 27 volunteers without known disease. Reproducible waveforms were obtained with the following means and standard deviations: (1) latency from stimulus to onset of sound, median = 6.9 +/- 0.8msec, ulnar = 6.6 +/- 1.0msec; (2) latency from stimulus to peak of sound, median = 15.1 +/- 1.5msec, ulnar = 13.1 +/- 1.5msec; (3) latency from onset of surface electric to onset of sound, median = 3.6 +/- 1.0msec, ulnar = 3.9 +/- 1.1msec; (4) baseline-to-peak amplitude of sound, median = 860 +/- 270mV, ulnar = 640 +/- 230mV; and (5) baseline-to-peak amplitude of surface electric, median = 11.4 +/- 3.0mV, ulnar = 10.1 +/- 2.4mV. Stimulated muscle sounds are useful when artifacts, such as tremor, interfere with voluntary muscle sound recordings, or when quantitative information is needed to relate electric to contractile muscle activity.