M RMS - AN EMG METHOD FOR QUANTIFYING UPPER MOTONEURON AND FUNCTIONALWEAKNESS/

A new method for quantifying upper motoneuron (UMN) weakness using sta ndard EMG equipment is presented and compared to the twitch occlusion method. Control subjects and patients with stroke, spinal cord injury (SCI), and peripheral nerve injury (PNI) were evaluated. Force, EMG, a nd twitch force from nerve electrical stimulation were recorded during isometric contractions of the biceps and triceps. Ratios of the elici ted CMAP amplitude (M)/voluntary-root-mean-square EMG activity (RMS) a nd of the voluntary contraction twitch force (T-i)/ the resting twitch force (T-max) were the two measures of UMN weakness studied. Both rat ios are linearly correlated with force for controls, log M/RMS (r = 0. 96) and T-i/T-max (r = 0.86). Log M/RMS ratio was abnormally high (> m ean + 2 SD; i.e., > 1.09) for weak muscles affected by stroke and inco mplete SCI, but was normal in muscles weakened by PNI. An elevated M/R MS ratio, may aid in quantification of deficient supraspinal activatio n from UMN or functional weakness. (C) 1994 John Wiley & Sons, Inc.