Background: In the previous studies, the results from power spectrum frequency changes at different sustained forces have been quite conflicting. This was the result of enormous changing in firing rate and motor units recruited; these were deciding factors of electromyographic power spectrum. The aim of this study was to investigate the characteristics of rate coding and electromyograph (EMG) interference pattern in two EMG-computer sets.
Methods: Thirty-nine healthy subjects were included in our study. Each was in a relaxed sitting position with forearm, wrist, and metacarpophalangeal joints fixed by straps. Two surface electrodes were attached to the muscle belly of extensor digitorum communis. EMG signals were processed at 10%, 25%, 50% and 100% of maximal voluntary contraction (MVC) using visual feedback from a dynamometer.
Results: The amplitude in dB remained constant at different isometric forces. The rate-coding parameters showed non-significant decrease as the percentage of MVC increased, ashereas the time-domain parameters revealed significant increase with stepwise increase in force.
Conclusions: EMG power spectrum analysis provides an easy, painless way of assessing global recruitment/rate descriptions of motor units.