METHODS TO REDUCE THE VARIABILITY OF EMG POWER SPECTRUM ESTIMATES

Three methods that can significantly reduce the variability of the EMG power density spectrum (PDS) variable by eliminating artifactual comp onents are described. Two methods: one that allows the subtraction of power line noise in the time domain and one which allows the subtracti on of system noise in the frequency domain from the EMG? were shown to be effective in helping to accurately estimate the median frequency ( MF) of the PDS, and especially during low level contractions (0-25% ma ximal voluntary contraction, MVC) when the signal-to-noise ratio is un favorable. The techniques eliminate the artifactual effects of system and power line noises from the EMG recordings throughout the force ran ge (0-100% MVC) while preserving the native EMG power at all frequenci es. It was also shown that if a technique to train subjects to produce their true MVC is employed, the absolute force/torque produced could be as much as 30% higher than in untrained MVC. The effect of true MVC production was also shown to be significant when interpretation of PD S variables are correlated to the processes which produce contraction. (C) 1998 Elsevier Science Ltd. All rights reserved.