Spatial Aliasing and EMG Amplitude in Time and Space: Simulated Action Potential Maps

Abstract

Average Rectified Value (ARV) and Root Mean Square (RMS) are the two amplitude indicators that are commonly used in the field of EMG. These two indicators are compared a) analytically for a one dimensional single sinusoid, sum of sinusoids, two dimensional sinusoids, and b) numerically by simulating a high density detection system for sampling the distribution of propagating surface action potentials generated by a muscle motor unit (MU). Results show that the RMS does not depend on the sampling rate while ARV does, even when the sampling theorem is satisfied. This is important since, in high density surface EMG detection systems (HDsEMG), the inter electrode distance (IED) samples the surface potentials often below the Nyquist frequency, generating aliasing in space. The largest IED that avoids spatial aliasing for the simulated MU is 10mm. IEDs below this value are recommended for experimental measurements.