抄録
We measured and analyzed a mechanomyogram (a record of muscle sound, MMG) of a human's biceps brachii when it is electrically stimulated. The biceps brachii was stimulated by electrical pulses with an EMS machine. The frequency and the amplitude of the pulses were 5 Hz and 11 V, respectively. The MMG was measured with a wideband acoustic emission (AE) sensor attached between the two electrode pads of the EMS machine. The MMG and the EMS pulses were measured simultaneously to investigate the muscle response to a single EMS pulse. It was confirmed that the MMG induced by the EMS appears soon after the EMS pulse and disappears in about 30 ms. The latent time, contraction time, relaxation time of the MMG were about 7 ms, 12 ms, and13 ms, respectively and the waveform of the MMG is similar to that of muscle force when a muscle twitches by low frequency EMS pulses. This suggests that the MMG and the muscle force during the twitch have the same kind of information. A scalogram was calculated by continuous wavelet transform and it was demonstrated that the MMG induced by the EMS exists in a frequency range of 10-100 Hz. This indicates that the muscle fibers vibrate concurrently with the dimensional changes and the gross lateral movement of the muscle.
