Motor unit contribution to surface-EMG. I. Experimental findings

Insight in the "building-stones" of EMG is essential for a proper interpretation of one of the most widely applied electrophysiological techniques. In the present paper, results from a comprehensive study on the contribution of single motor units (MUs) to surface EMG recordings are presented. This study gives insight in the contribution to the surface EMG of the motor unit potentials (MUPs) of motor units at different depths below the skin. It is shown that a distinct difference between the positive and the negative peak of MUPs exists, the latter with a more steep amplitude decline with MU depth. The signal area of the MUPs is least affected by the depth of the MU.