SINGLE-SITE ELECTROMYOGRAPH AMPLITUDE ESTIMATION

Previous investigators have experimentally demonstrated and/or analytically predicted that temporal whitening of the surface electromyograph (EMG) waveform prior to demodulation improves the EMG amplitude estimate [1]-[6]. However, no systematic study of the influence of various whitening filters upon amplitude estimate performance has been reported. This paper describes a phenomenological mathematical model of a single site of the surface EMG waveform and reports on experimental studies which examined the performance of several temporal whitening filters. Surface EMG waveforms were sampled during nonfatiguing, constant-force, isometric contractions of the biceps or triceps muscles, over the range of 10-75% maximum voluntary contraction. A signal-to-noise ratio (SNR) was computed from each amplitude estimate (deviations about the mean value of the estimate were considered as noise). A moving average root mean square estimator (245ms window) provided an average +/- standard deviation (A+/-SD) SNR of 10.7 +/- 3.3 for the individual recordings. Temporal whitening with one fourth-order whitening filter designed per site improved the A+/-SD SNR to 17.6 +/- 6.0.