Signal characteristics of EMG with special reference to reproducibility of measurements.

Reliability and constancy of recordings of EMG signal characteristics were investigated from the measurements taken with miniature size surface electrodes during submaximal and maximal contraction of the rectus femoris muscle. The following EMG variables were studied: integrated EMG (IEMG) various bandwidths of the power spectral density function, mean power frequency (MPF), and rise time, amplitude and number of spikes of the averaged motor unit potential (AMUP). The results indicated that for most of the variables studied the reproducibility of measurements was better within the test session (reliability) than between the different test days (constancy). The reliability values for IEMG, MPF and AMUP amplitude were rather high (r=0.77-0.93) and it is suggested that these parameters can be recommended for use in EMG studies where recordings are repeated over a period of several days.