Reproducibility of surface EMG variables and peak torque during three setsof ten dynamic contractions

The interpretation of the electromyogram (EMG) of dynamic contractions migh t be difficult because the movement per se introduces additional factors th at could affect its characteristics. There is a lack of studies concerning the reproducibility of surface EMG registrations during dynamic contraction s. The aim was to investigate the during-the-day reproducibility (using int ra-class correlation; ICC) of the peak torque (PT) and the EMG Variables (w ithout removing the electrodes) of dynamic contractions. Ten healthy subjec ts performed three sets of 10 dynamic maximum right-knee extensions with a one-hour interval in between, using an isokinetic dynamometer and the PT wa s determined. EMG signals were recorded from the right vastus lateralis, re ctus femoris and vastus medialis muscles using surface electrodes and the m ean frequency of the power spectrum (MNF [Hz]) and the signal amplitude (RM S [mu V]), were computed. The ability to relax in-between the maximum exten sions was calculated as a ratio of the RMS during the passive flexion phase and the RMS during the active extension phase of each contraction cycle: t he signal amplitude ratio (SAR). Both PT (ICC = 0.99) and RMS (ICC = 0.83-0.98) had good reproducibility. Th e reproducibility of MNF was good for all muscles when the mean of contract ion nos.: 1-10 was used. Vastus lateralis had the highest ICC among the thr ee muscles. The reproducibility of SAR was generally poor (ICC < 0.60). The present study showed good reproducibility for common EMG Variables (MNF an d RMS) obtained during maximum isokinetic contractions. (C) 1999 Elsevier S cience Ltd. All rights reserved.