Evaluation of the Long-term Reliability of Motor Uni Discharge Rates obtained by Decomposition of the Surface Electromyographic Signal

This study evaluated the long-term reliability of motor unit discharge rates (MUDRs) during isometric contractions at 60% maximum voluntary contraction (MVC), obtained by decomposition of the surface electromyographic (sEMG) signal from the flexor carpi radialis (FCR) and tibialis anterior (TA). There were four test sessions: one week between sessions 1 and 2; six weeks between sessions 2, 3, and 4. Participants performed 3 maximal isometric contractions of the wrist flexors and 3-isometric ramp contractions to 60% MVC. A load cell and 5-pin electrode (dEMG System, Delsys, Inc., Boston, MA) were used to monitor force and sEMG, respectively. The MUDRs were obtained using the Precision Decomposition Algorithm III in the dEMG Analysis software, and calculated as the inverse of the smoothed firing intervals. The mean discharge rate was calculated during a one-second window centered at the plateau portion of the 60% MVC ramp contraction. Maximal isometric strength during wrist flexion and dorsiflexion was also monitored. Across the four test sessions, maximal isometric strength of the wrist flexors and dorsiflexors increased 10 and 11.85%, respectively (p’s0.94). The MUDRs for the FCR (5.2%) and TA (7.8%) also exhibited slight fluctuations across the four test sessions (p’s