Neuromuscular electrical stimulation
Gorgey, Ashraf Sherif
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These studies examined the effects of surface neuromuscular electrical stimulation (SNMES) control components, pulse duration, frequency of the pulses and amplitude of the current, on specific tension (ST) and muscle fatigue. The outcome of a SNMES protocol used in research was also compared to a common rehabilitation protocol. Magnetic resonance images of both thighs were acquired prior to and after SNMES to determine the area of stimulated muscle. Fatigue was assessed by the decline in torque during 3-5 minutes of SNMES. One of five SNMES protocols was applied to either knee extensor muscle group to induce isometric actions. The amplitude of current that evoked torque equal to 45% or 75% of maximum voluntary 2isometric torque did not alter ST, 25 N/cm. Increasing the pulse duration from 150 to 450 µs 2caused ST to increase from 20 to 25 N/cm. Increasing the frequency from 25 to 100 Hz 2increased ST from 17 to 25 N/cm by increasing the evoked torque. ST using the activated area 2vs. assuming the whole muscle area was recruited was 25 vs. 15 N/cm. Increasing the frequency from 25 to 100 Hz increased fatigue from 39 to 76%. Increasing the pulse duration and the amplitude of the current did not. The results suggest that the frequency but not the amplitude of current nor pulse duration of SNMES affects fatigue. ST was double for the research protocol (RP) compared to the rehabilitation protocol (REH P). REH P did not show maintenance of torque at the beginning or end of the 10 sec contractions over the 5 min. Torque decreased 31% and 50%, respectively. Nonetheless, overall fatigue was lower in REH P compared to the RP. These results suggest that 1) ST is higher using the activated area vs. assuming the whole muscle area was recruited, 2) The amplitude does not alter ST, 3) increasing the frequency of SNMES increases ST, 4) The pulse duration modestly increases ST, 5) fatigue during SNMES is dependent on the frequency of the pulses and 6) the REH P was not designed to optimize ST, but it elicited less muscle fatigue than RP.