A completely automated system for determining the number of motor units in a skeletal muscle has been developed and tested. It is based on the McComas incremental motor unit counting technique and eliminates the subjectivity introduced by the operator's judgement and addresses the problem of alternation which plaques manual estimation techniques.
The system, currently implemented using a PDP-11/34 mini computer, uses silver strip electrodes to record the electrically evoked electromyographic responses which are amplified, filtered, and digitally converted for computer processing, display, and storage. The software uses digital signal processing, pattern recognition, and complex algorithms with well defined decision criteria to vary the stimulus amplitude, classify the responses, identify alternation, and estimate the motor unit count. The system was extensively tested on the thenar and extensor digitorum brevis muscles of numerous subjects. Its performance compared favourably with that of an experienced manual operator.
The speed, reliability, and objectivity of the system make it very useful clinically and promote the standardization of motor unit count estimation.