Influence of the motor unit action potential morphology (MUAP) on the EMG signal: theoretical and experimental study

The aim of this work is the study of the influence of the MUAP morphology on the compound EMG signal by means of a simulation model. The simulated EMG is obtained as the sum of a number of MUS chosen on the basis of considerations concerning the muscle fiber dimension, the concentric needle electrode uptake area and the conduction volume. Myopathic and neurogenic conditions have been simulated together with the normal case, adopting typical MUAPs. The interspike interval (ISI) has been simulated by means of a stochastic variable. Both time and frequence domain analysis have been performed in the simulated EMG. The parameters obtained have been compared with those obtained from the experimental EMG in corresponding groups of pathologies. The model has provided clarifying data concerning the influence of the morphology of the MUAP, confirmed by the experimental findings. Simulation of abnormalities in the firing pattern as well as in the recruitment, seems to be necessary in order to improve the prediction capabilities of the model.