System identification of mechanomyogram in voluntary contraction of abductor digiti minimi muscle

The purpose of this study is to establish a method for identifying the transfer function between the electromyogram (EMG) and mechanomyogram (MMG) in voluntary contraction of the abductor digiti minimi muscle using a system identification method. An MMG and EMG in twitch-like contraction were measured. The measurements were repeated ten times. The EMG was full-wave rectified and then smoothed with a low-pass filter (fc=100 Hz). The smoothed EMG and the MMG were regarded as an input and an output of the system, respectively. The transfer function was identified with the subspace state space system identification method. The transfer function could be approximated with a third-order model for all subjects in five measurements or more. It was suggested that the MMG system was identified in voluntary contraction.