Identification of a single motor unit by grid surface electrodes - A new three dimensional expression of surface EMG

The surface electromyogram (sEMG) is an indication of muscle activity and it is important for sports training and rehabilitation. The aim of this study is development of a new interface in order to visualize the aspect of conducting motor unit action potential (MUAP) for multi channel sEMG measured by grid surface electrodes. Conventionally, the multi channel sEMG is displayed as only a time chart of each channel according to the spatial arrangement of the surface electrodes. Therefore, it is difficult to understand the total spatial and temporal aspects of time varying potential distribution on the skin surface. We proposed a new visualization method of multi channel sEMG in order to obtain the total aspects at a glance. In this method, we first developed the grid surface electrodes in which seven differential sEMGs were arranged linearly (column: x direction) as one unit and these eight units were set parallel (row: y direction) with each other. We could obtain 56-channels sEMGs from the grid electrodes. Then, we interpolated the 56-channel signals along x direction by the cubic spline function and after that interpolated them along y direction also by the same cubic spline function. And we obtained a continuous potential distribution on x-y plain surface by such interpolation. Repeating this process on all time sampling data, we could finally obtain a three dimensional (x-y-t) distribution of the sEMGs. Using this distribution, we could edit an animation where each frame showed the potential distribution as a curbed surface on the x-y plain. We can clearly recognize the total spatial and temporal aspects of time varying potential distribution on the skin surface using this new three dimensional expression of surface EMG. Because of this visual expression, we might clearly find the anatomical position of neuromuscular junction and also the interference of two independent motor unit action potential waves.