Measuring the influence of activity on the impedance of EMG electrodes

Electro-myography (EMG) provides a non-invasive method to index the level of muscle activity. It has many applications, such as identifying the phase of muscle activity during performance, calculation of muscle fiber conduction velocity and identification of specific neuromuscular pathologies. Besides, it can also be used to detect the onset and progression of muscular fatigue. EMG is considered to be a promising candidate for the control of exo-skeletons. Not only because it can be a very intuitive way of controlling an exoskeleton, also because it has many advantages compared to e.g. control executed via buttons.

EMG encounters some problems when recording long-term: wet EMG electrodes may dry out and the activity may induce motion artefacts, EMG activity induced by other electrical components, noise and the relatively low signal-to-noise-ratio (SNR). To take in to account or reduce the amount of noise present in the signal, the sources of noise have to be identified and kept to a minimum. A potentially large source of noise is that caused by the electrode-skin interface, which consists of a combination of voltage and current noise. When the electrode-skin impedance is high, the importance of current noise is increased.

The quality of an EMG measurement is determined for a large part by the impedance of the electrodes. However, little is known about how the impedance spectrum of different electrodes is influenced by activities. In this assignment, an attempt will be made to better characterize and understand these noise sources. As a part of this process impedance measurements will be performed on subjects. To do these measurements both standard and customized electrodes will be used.