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Motor unit contributions to the surface-EMG. II. Theoretical basis

In the analysis of surface EMG signals, one of the most important issues to address is the question which motor units are investigated: where are the contributing units located and to what extent is "looking into the muscle" possible. The answer to these questions strongly depends on the behavior of signal amplitude with source depth. In the present paper, this behavior is investigated with the aid of an analytical volume conductor model. For natural values of volume conductor and source parameters, good agreement is obtained between model and experimental results. Changes in these parameters are shown to have major consequences on the behavior of amplitude with source depth.