Filter banks and the "Intensity Analysis" of EMG

TL;DR

This paper investigates Vinzenz von Tscharner's intensity analysis method for EMG signals, clarifying its mathematical basis, connection to wavelet analysis, and demonstrating its application to dynamic EMG data.

Contribution

The paper provides a mathematical clarification of the intensity analysis method, linking it to wavelet theory and simplifying its formulation with Morlet wavelets.

Findings

The method is mathematically connected to wavelet analysis.

Simplified formulation using Morlet wavelets is proposed.

Applied successfully to nonstationary EMG signals.

Abstract

Vinzenz von Tscharner (2000) has presented an interesting mathematical method for analyzing EMG-data called "intensity analysis" (EMG = electromyography). Basically the method is a sort of bandpassing of the signal. The central idea of the method is to describe the "power" (or "intensity") of a non-stationary EMG signal as a function both of time and of frequency. The connection with wavelet theory is that the filter is constructed by rescaling a given mother wavelet using a special array of scales (center frequencies) with non-constant relative bandwidth. Some aspects of the method may seem a bit ad hoc and we have therefore undertaken a closer mathematical investigation, showing the connection with the conventional wavelet analysis and giving a somewhat simplified formulation of the method using Morlet wavelets. It is pointed out that the "intensity analysis" method is related to the concept of an equalizer. In order to illustrate the method we apply it to nonstationary EMG-signals of a dynamic leg-extension force-velcity tests. (Data provided by Taija Finni, University of Jyv\"askyl\"a.)