Low-pass filter effect in the measurement of surface EMG

Many publications and articles describe the electrical properties of muscular tissue. In these articles the terms "low pass filter" and "purely resistive medium" often occur in parallel. From the viewpoint of electrical engineering (namely from a network theoretic viewpoint) one would not expect that a purely resistive medium behaves as a low pass filter. Instead the existence of some capacitive and/or inductive elements would be expected. We present a network theoretic description of the low pass filter effect of muscular tissue. We use a descretized and simplified tissue model, e.g. a network of resistors. For this model the low pass characteristic of muscular tissue will be verified. The fundamental reason for the low pass characteristic of muscular tissue is the fact that electrical activity travels with some constant velocity along a given path (e.g. the muscle fibres) while the measurement of this activity is done at some fixed point. The independant variables "time" and "space" can be mapped onto each other. The low pass filter effect occurs in space domain.