Consistency of surface EMG patterns obtained during gait from three laboratories using standardised measurement technique

The paper investigates the consistency of EMG recordings of gait obtained in three different laboratories using a standardised measurement technique. Ensemble averaged surface EMG profiles were recorded in rectus femoris, semitendinosus, tibialis anterior, and gastrocnemius medialis muscles in a group of 20 normal subjects who walked at comfortable walking speed. Each subject was studied in three separate laboratories and the data were compared. Experimental protocols and electromyographic instrumentation were standardised and functionally equivalent footswitch systems were used. Consistency of the shape of the subjects' profiles across laboratories was described using correlation coefficients. The signal magnitudes were compared using the coefficient of variation and mean value of profiles. The across-laboratory inter-subject variability was determined for peak, onset and cessation times of EMG activity. A marked similarity in the shape of profiles across laboratories was found. Times of peak, onset and cessation of EMG activity were repeatable within few percent of the gait cycle. The absolute magnitude of the profiles was less consistent. The results of this study suggest that meaningful exchange of EMG data amongst laboratories for multi-centre trials and teleconsultation purposes is possible. The study underlines the value of EMG recording as a tool in gait analysis. It is concluded that standardisation of instrumentation, experimental protocols and data processing techniques is strongly needed.