Muscle Fatigue and the Importance of Electrical Stimulation Parameters on Functional Electrical Stimulation

Different combinations of stimulation parameters can create outcome variations during Functional Electrical Stimulation (FES). This study compared muscle performance and time until fatigue for four different parameter combinations. Standard Protocol used 20 Hz, 200 mu s pulse width, and minimum current to evoke movement; Long Pulse Duration (LPD) Protocol utilized 20 Hz frequency, 500 mu s pulse width, and minimum current; High Frequency (HF) 100 Hz, 200 mu s pulse width, and minimum current; and High Amplitude (HA) used 20 Hz frequency, 200 mu s pulse width, and current 25% above the minimum to evoke movement. The results of the present study indicate that higher current amplitudes seemed to slightly positively influence the outcome of the tests but at the cost of greater subject discomfort. Longer pulse durations seemed to produce stronger contractions and further muscle endurance. However the primary outcome of this experiment has to be the finding that the extent and onset of fatigue during ES depends mainly on the frequency of the pulses.