New Measurement Techniques of Surface Electromyographic Signals in Rest Position for Application in the Ophthalmological Field

Abstract

Some guidelines are given for the interpretation of the electromyogram (EMG). In static isometric contractions there is, usually a linear, relationship between muscle force and smoothed rectified EMG (SRE). It should be considered, however, that most of the time several muscles are active simultaneously around a joint. This finding implies that the relationship between the SRE of a single muscle and the total joint moment needs not be linear. During movements, the force-length-velocity relationship and the elastic properties of muscle should be taken into account. Also, EMGs during concentric movements are larger than those measured during isometric actions. A further consideration in relating force to EMG is that the force signal has a much lower frequency content than the rectified EMG. Finally, the limited speed of the activation and deactivation process results in a 50 to 200 ms delay of the muscle force relative to the EMG.