Non-stationary analysis of EMG activities prior to a ballistic movement.

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The electromyographic (EMG) signal which is an indication of the electrical activities in contracting muscle is of value in the study of the motor control mechanism. In a ballistic voluntary movement following a slight sustained contraction, the EMG activity abruptly changes from a tonic discharge to a phasic discharge. An electrical silence or decrease appear just before the onset of the phasic activity. The present study placed focus on a myoelectric activity prior to the ballistic voluntary movement. The EMG activity was processed as a non-stationary stochastic process, and the statistical properties, particularly, the probability density function, were analyzed.The EMG process remained stationary and normally distributed up to 100 msec before the initiation of the phasic activity. Subsequently, the probability density changed to indicate non-Gaussian property. Statistical test verified this property was statistically significant from 50 msec prior to the onset of the ballistic discharge. As a result of the orthogonal expansion of the probability density function, coefficients of 4th and 6th orders increased from approx. 60 msec before the phasic EMG. These analytical results suggested that the depression of the EMG before the initiation of the ballistic movement was due to an active physiological mechanism with a special programming it the upper center.
一般社団法人日本生体医工学会の論文