Two dimensional propagation of displacement mechanomyographic signal

Skeletal muscle consists of large numbers of motor units, each of which fires independently during voluntary contraction. The myoelectric signal which is recorded on the skin surface, namely a surface electromyogram (sEMG), is a time-related and spatial aggregate of the action potentials of these motor units. The sEMG indicates the input information for muscle contraction when the skeletal muscle is regarded as a system function. On the other hand, Mechanomyographic signal (MMG) is a skin surface vibration caused by muscle contraction and recorded by an accelerometer, a microphone, a displacement transducer, and other devices. The MMG directly reflects the activity of muscle contraction. But MMG's two-dimensional generation mechanism is still not clarified in detail, because the simultaneous multipoint measurement procedure and analytic technology of mechanomyographic signal have been insufficient. In this study, the displacement MMGs were recorded at 21 measuring points within 2x6 cm by using the displacement transducer, and MMG maps were described, while the motor points of the biceps brachii were electrically stimulated. The spatial propagation of twitch waveform of d-MMG was also discussed. As a result, it was clarified that the waveform amplitude decreased with propagation along the longitudinal axis of muscle fiber and it was estimated that the propagation velocity was 5-8m/s. But the positional relation of the axis of muscle fibers and measuring points affected the amplitude of propagation velocity.