PHONOMYOGRAM FROM SINGLE MOTOR UNITS DURING VOLUNTARY ISOMETRIC CONTRACTION

The purpose of this study was to determine the characteristics of the specific phonomyogram (PMG) of active motor units activated during vol untary isometric contractions. The electromyogram (EMG) and PMG were r ecorded from 87 anconeus motor units in 14 subjects. The elementary PM G from single motor units was analysed with a spike-triggered averagin g technique. The electro-acoustical delay was 3.5 (SD 1.1) ms, which i s within the range of values reported in the literature for PMC evoked by motor nerve stimulation. All motor units demonstrated a pattern of impulsive sounds with a duration of 87.2 (SD 10.7) ms. These results would imply that PMG is linked to the contractile activity of the moto r units. These results also would suggest that PMG recorded from a con tracting muscle in situ reflects the summation of elementary PMG durin g voluntary contraction more than the overall mechanical properties of the muscle.