Multielectrode surface EMG for noninvasive estimation of motor unit size

To noninvasively estimate the motor unit size, we present a novel surface e lectromyographic (EMG) measurement system consisting of a surface multielec trode with four-pin electrodes and a pair of surface-disk electrodes. Surfa ce motor unit action potentials (MUAPs) were recorded with the multielectro de, in the so-called multielectrode surface EMG (MSEMG), which was spatiall y filtered to localize the sensing area and reduce the noise. In addition, a modified decomposition algorithm, considering the geometrical configurati on of the multielectrode, was designed to identify the individual MUAPs in the measured MSEMG. The identified MUAP was subsequently used as the trigge ring source for the EMG signals recorded by the surface-disk electrodes. Fr om a pool of 34 subjects with neuromuscular diseases and 14 normal subjects , the median amplitudes of surface-disk EMG after spike-triggered averaging , called MSEMG-MUAP, correlated well (r = 0.82, P < 0.0001) with those of m acro EMG. Moreover, the MSEMG-MUAP recording during a ramp force contractio n exhibited the common size principle phenomenon during motor unit recruitm ent. The results of this study demonstrate that the MSEMG-MUAP measurement is a feasible approach for estimating the motor unit size from the skin sur face. (C) 1999 John Wiley & Sons, Inc.