Simulation of macro EMG motor unit potentials.

Macro EMG motor unit potentials (MUPs) have been simulated. The effects on MUP parameters of number of fibres, fibre diameter, end-plate scatter, nerve branch delay, motor unit territory and electrode position have been studied. The MUP shape is sensitive to electrode position in the vicinity of the end-plates. It is mainly reflecting the end-plate scatter and the nerve delays. Away from the end-plates the wave shape is principally determined by the fibre diameter distribution. Total number of muscle fibres and their mean diameter act as gain factors at all recording positions. In the simulations the area of the signal appears to be a better measure of the strength of the motor unit than the amplitude. Macro EMG offers a much less selective recording than conventional EMG and single fibre EMG and therefore new aspects of the motor unit can be quantified. Preliminary results from simulations of neuromuscular disorders are consistent with actual findings.