Effects of refractoriness variation on the interpulse interval statistics at the output of the neuromuscular junction

The variation in refractory period of muscle fibers has not been studied systematically in electromyography (EMG) forward modeling, although changes in cell excitability are observed experimentally in some myopathies. The e. ect of the absolute refractory period variation at the postmembrane of a neuromuscular junction is theoretically analyzed in this work for the input stimulus with exponentially and normally distributed interpulse intervals (IPIs). Mathematical expressions on the probability density function (p.d.f.) of the output IPIs are carried out for both cases. The comparison is made between the theoretical and simulated results of output IPI probabilities and mean firing rate for di. erent values of absolute refractory period. It has been demonstrated that the theoretical results are consistent with simulated ones. The output mean firing rates will be reduced when increasing the value of absolute refractory period at the postmembrane for exponential cases, while for Gaussian cases, it will keep almost unchanged at first, then decrease dramatically with the continuous increasing of the absolute refractory period. The results of this work may provide an aid in understanding clinical surface EMG for certain muscle diseases.