Isometric Tension and Electromyography during Functional Electrical Stimulation of the Rat Hindlimb Muscles.

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Objective : To clarify electrically-induced muscular fatigue, the relationship between muscle tension and the electromyography was investigated in the rat hindlimb muscles.Methods : Male Wistar rats (16-week-old) were included. Under general anesthesia, tibialis anterior (TA) and soleus (SOL) muscles were exposed and their distal tendons were attached to the force transducer to measure the isometric tension. A small electrode array consisting of stimulating needles and recording bars was placed over the muscle belly, and tetanic electrical stimulation was applied for 30 seconds at a frequency of either 20Hz or 40Hz. Peak-to-peak amplitude and peak latency of the M-wave, and the muscle fiber conduction velocity (MFCV) were analyzed. The MFCVs were corrected to the temperature of 26℃.Results : During tetanic electrical stimulation, progressive amplitude depression and latency increase of the M-waves as well as slowing of the MFCVs were found which were always preceded by decline of the isometric tension. The speed of these changes differed significantly between TA and SOL muscles and between 20 and 40 Hz of stimulation frequencies.Conclusion : Monitoring the M-waves, especially their amplitudes, seems valuable for detecting muscle fatigue before actual tension drops. The results may be of value for automatic control of functional electrical stimulation for the paralyzed muscle in the field of rehabilitation medicine.