Consistency of multi-channel surface EMG recordings: Application in spinal cord injured subjects

We evaluated the consistency of serial polyelectromyographic recordings of altered motor control in spinal cord injured (SCI) individuals. Using 12 pairs of surface electrodes placed over major muscle groups of lower limb and trunk, we examined voluntary and involuntary and phasic and tonic features of motor control using a standardized protocol for brain motor control assessment (BMCA). The surface electromyographic (EMG) data were digitized and analysed on the basis of the root mean square (RMS) envelope of activity, with the exception of phasic tendon tap responses which were evaluated from full bandwidth EMG data. The average amplitudes of responses were calculated. The median correlation of the results from two successive examinations 1-2 weeks apart for all subjects was 0.98. Further analysis was based on ratios of corresponding elements from the two studies. Noise from null responses was suppressed by incorporating a threshold parameter T set to 1 muV(RMS). With this value, pairs of studies in 52 subjects were virtually identical (mean ratio of 1.02 +/- 0.1). Z-scores from two case studies in which pharmacological and physiological interventions changed motor control demonstrated the utility of the procedure. This method offers a reliable and appropriate means of studying altered motor control which is sensitive to changes induced after interventions.