Non-invasive quantitative EMG.
The EMG information obtained by surface recording is compared to needle derived data processed in an identical manner. Such quantitative analysis of EMG activity has been undertaken using needle electrodes and is a well recognised technique for clinical purposes (16). Results of a study comparing data collected simultaneously by surface and needle electrodes from normal healthy volunteers are presented as a preliminary to a similar study of neuropathic and myopathic patients. The EMG interference pattern during maximum voluntary contraction was analysed for turns and zero crossings as well as from frequency spectral data, and the results displayed on-line using an inexpensive novel transputer aided PC. It was found that quantitative studies of surface and needle data were directly comparable in one muscle such as tibialis anterior but very different in another, such as rectus femoris, where there were changes in signal characteristic at different depths. The variability between individuals appeared to be less marked when surface electrodes were used. Data from surface recordings also show a high degree of repeatability when collected over a period of time.