Modeling Myoelectric Activity

Abstract

The electromyogram (EMG) is a recording of the electrical activity of muscles (also termed myoelectric activity). The EMG is recorded by placing biopotential electrodes close to the muscle of interest. The EMG is usually recorded during voluntary action of the muscles; the signal evoked from muscles by artificial electrical stimulation is called the compound muscle action potential (CMAP). The recorded signal depends upon the anatomy of the muscle and the recording electrode arrangement as well as the physiological activity. It is important to understand the effect of the recording arrangement in order to discount the peculiarities of the recording setup during analysis. Different analytical techniques focus on the anatomical structure (e.g., distribution of the neuromuscular junction, size and distribution of motor units, etc.), or on the physiological behavior (e.g., degree of activation, neuronal firing patterns, the fiber conduction velocity, muscle fatigue, etc.). We shall develop a model of the recorded electromyogram which can be used for understanding the different components in its generation; this will, we hope, lead to a logical understanding of analytical techniques for EMG processing. We shall deal mainly with the voluntary EMG since it is the more general signal. The compound muscle action potential is simply a special case where the neuronal firing pattern is replaced by a simple deterministic function, usually the unit impulse, δ(t).