Inference of motor unit recruitment order in voluntary and electrically elicited contractions

DE LUCA. Inference of motor unit recruitment order in voluntary and electrically elicited contractions. J. Appl. Physiol. 68(4): 1657-1667, 1990.-The relationship between surface myoelec-tric signal parameters and the level of voluntary or electrically elicited contractions was studied in 32 experiments on the tibialis anterior muscle of 22 healthy human subjects. Contrac-tions were performed at 20 and 80 % of the maximum voluntary contraction torque. Two levels of stimulation current were used, yielding, respectively, a maximum M wave and an M wave-30 % of the maximum. A four-bar electrode probe was used to detect single- and double-differential signals from which mean and median frequency of the power spectrum and average muscle fiber conduction velocity were estimated. Measurements obtained from voluntary contractions showed a positive corre-lation between contraction levels and both conduction velocity and spectral parameters. Conduction velocity increased by 21.