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ABSTRACT A distributed random electrical neuromuscular stimulation (ENMS) of ten ventral root channels was used in this study to stimulate cat soleus muscle. The influence of varying inter-stimulus intervals (ISI) and the interaction of the ISI statistics with the compound motor unit EMG power action potential (CMUAP) on spectra were assessed theoretically using a mathematical model and experimentally using the data obtained from cat soleus muscle. Theoretical and experimental results suggest that (1) the interaction of the ISI statistics with the shape of the CMUAP significantly influence the EMG spectrum; and (2) that the EMG spectrum of electrical random stimulation of muscle shows peaks at the mean rate of stimulation and multiples of it when the ISI variation coefficient is small, and that these peaks decrease in magnitude with increasing frequency and increasing values of the coefficient of variation of ISI. I. INTRODUCTION For ENMS to work satisfactorily in a given situation, it is necessary to select proper stimulation parameters and employ stimulation strategies in accordance with findings from research in electrophysiology. A literature review of electrophysiological studies of muscle identifies the following important points [1, 2, 4, 5, 8]: 1) voluntary contraction of skeletal muscle is controlled by the number of motor units, which are progressively recruited according to the size principle, and the rate of firing of each unit; 2) Signals from active motor units are uncorrelated during low and medium voluntary efforts, and become synchronized at high efforts; and 3) Firing of alpha motor neurons is a random process, ie, the time interval between …