Mathematical model of the summated electromyogram based on the probability characteristics of single motor units.

A probability model for synthesis of the summated electromyogram (EMG) is elaborated on the basis of previous experimental work describing the probability characteristics of the firing of single motor units (MUs) subjected to different external disturbances (e. g. stretch or unloading) and following different instructions for voluntary activation. The possibility is demonstrated some maxima in the summated EMG to be due not to increases excitability of the alpha-motoneurones but to synchronization of the impulses after application of external disturbance, whereby the probability for appearance of impulse in some time intervals will disturbance, whereby the probability for appearance of impulse in some time intervals will increase. The proposed model is used for qualitative studies as a number of factors influencing the value of the signal recorded upon leading off of summated EMG are not taken into account.