ELECTROMYOGRAPHIC SIGNALS DURING GAIT - CRITERIA FOR ENVELOPE FILTERING AND NUMBER OF STRIDES

The use of linear envelopes to represent the electromyographic (EMG) m easurements obtained during locomotion has become common practice. Gui delines for designing envelope filters and specifying the minimum numb er of strides needed to produce valid EMG profiles have been developed . Electromyograms from eight major muscles of the lower leg are measur ed from five normal young adults during self-selected slow, free and f ast walking speeds. 30 strides per task are measured. The 'ideal' EMG profile is defined from the ensemble average of the rectified EMG sign al. An error measure is defined and used as a criterion to assess the appropriateness of various cut-off frequencies for envelope filters an d the number of strides required for establishing a good EMG profile. It is found that between six and ten strides are needed to form a repr esentative profile, and an envelope filter with a minimum cut-off freq uency of approximately 9 Hz is necessary.