EMG VARIABILITY DURING MAXIMUM VOLUNTARY ISOMETRIC AND ANISOMETRIC CONTRACTIONS IS REDUCED USING SPATIAL AVERAGING

Electromyography (EMG) is a commonly used tool that can be plagued wit h poor signal-to-noise ratios. One result of poor signal-to-noise rati os is increased within-and between-subject variability of quantified E MG variables, for example, the integrated EMG. Methods that reduce wit hin-and between-subject variability of quantified EMG variables can in crease the statistical power of an experimental design and aid in the functional interpretation of experimental results. The purpose of this investigation was to determine the effectiveness of spatially averagi ng the surface EMG signal to reduce the variability of the quantified EMG obtained during maximum voluntary contractions (MVC). The present study extends the work of earlier investigators describing the enhance d signal characteristics obtained by spatially averaging the surface E MG measured during submaximum voluntary isometric contractions and str etch reflexes. Ten subjects performed maximum voluntary isometric and anisometric (concentric and eccentric) contractions of the elbow flexo rs. Four electrodes, forming two pairs of bipolar electrodes were plac ed over both the biceps brachii and brachioradialis muscles. Four rect ified and integrated EMG signals from the electrode array were compare d. Data from each subject's contraction condition and from each muscle were used to compute a coefficient of variation that was considered r epresentative of the within-subject variability. These data were analy sed with a multifactorial repeated measures analysis of variance (ANOV A). The results revealed a muscle-specific, statistically significant superiority of one of the methods in reducing the variability of the r ectified and integrated EMG signal. Summing the rectified and integrat ed signals from each bipolar pair of electrodes in the array was shown to reduce significantly the within-subject variability. (C) 1998 Else vier Science Ltd. All rights reserved.