A high-density multichannel surface electromyography system for the characterization of single motor units

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Abstract
An electromyography (EMG) system is presented that noninvasively records the electrical activity of a muscle with 126 densely spaced skin-surface electrodes. The electrodes are arranged in a two-dimensional array and integrated in a single container for ease of application. Signals are recorded “monopolarly”, with a reference electrode placed at a distance from the array. With this recording configuration, the surface EMG (sEMG) potential distribution can be described not only as a function of time, but also topographically. The availability of topographical information opens up a range of applications. Some of these have been described previously. However, the system presented is unique in that it allows exploration of all clinical and scientific possibilities of topographical sEMG. In its design, special attention was paid to user-friendliness and flexibility. With high-density multichannel sEMG, both the properties of a whole muscle and those of single motor units, the functional units of a muscle, can be studied. The latter belong to a realm that was long considered accessible only with needle-EMG, a conventional, invasive diagnostic technique. It is demonstrated that the additional topographical information can be used to characterize motor units in a way that is partially superior to needle EMG.