MONITORING OF FES-INDUCED MUSCLE-ACTIVITY BY CONTINUOUS EMG-RECORDING

Functional Electrical Stimulation (FES) requires information on the st imulated muscle for adjustment of the stimulation current, avoidance o f muscle fatigue during the conditioning period and long term follow-u p. Several applications of chronical FES are in clinical practice, but a system for direct registration of muscle activity under FES still d oes not exist. In six sheep the right Latissimus Dorsi Muscle (LDM) an d Thoracodorsal Nerve were exposed. Stimulation electrodes were applie d to each nerve and 3 EMG-applied sensing electrodes were placed into each LDM. The LDM tendon was connected to a force transducer. Burst st imulation was applied and the amplitude was increased from 0 to 4 mA i n steps from burst to burst. EMG (M-wave) was amplified and recorded c ontinuously via modified instrumentation amplifier, oscilloscope and t ape recorder. Isometric muscle tension was recorded using force transd ucer, A/D interface and PC. Continuous EMG-recording was performed in all cases. Simultaneous recording of muscle tension and EMG revealed a close correlation (lrl = 0.95, p < 0.0001) between muscle strength an d amplitude of the M-wave. Continuous recording of the EMG seems to be a reliable method for direct monitoring of the stimulated muscle. Thr ee intramuscular electrodes can provide enough information to monitor FES induced muscle activity.