Frequency dependent modelling of single motor unit surface potentials

The modelling of surface electromyographic (SEMG) signals is important for the development of non-invasive diagnostic techniques. Although it is generally accepted that a quasi-static formulation of the volume conductor problem is valid, this has not been demonstrated in the context of the very detailed analyses currently being carried out on SEMG waveforms. Here we outline a novel technique for applying travelling action potential loads to a finite element model with frequency dependent tissue characteristics. The method is based upon a Fourier decomposition of the action potential at each node along the path of the moving source within the model. The results of the analysis show that, over a range of conductivities quoted in the literature, the quasi-static formulation is valid. The frequency dependent terms cause only a slight change in action potential shape at the surface.