A Comparison of Torque Generating Capabilities of Three Different Electrical Stimulating Currents

Abstract

The purpose of this study was to test the torque generating capabilities of three commercially available neuromuscular electrical stimulators (NMES) having different current characteristics.Twenty healthy adults were positioned in sitting on an isokinetic dynamometer. Maximum voluntary isometric knee extension torque was determined. Subsequently, two 10-sec, maximally tolerated contractions were elicited with each machine. The order of stimulation was randomized and there were 2-minute rest periods between contractions. Electrically elicited torque values were expressed as a percentage of the maximal voluntary isometric torque WMVIT).Analysis of variance with one repeated measure showed a significant difference among %MVIT produced by the stimulators. NMES 2 (Nemectrodyn 7) produced significantly less %MVIT than either NMES 1 (Electrostim 180-2) or NMES 3 (Chattanooga VMS). In all but three cases, NMES 2's maximal current output was reached. Although all three devices were capable of producing %MVIT that has been shown to be sufficient for strengthening, it appears that NMES 2 does not have the capacity to provide "overload" as strength increases.

Torque Responses in Human Quadriceps to Burst-Modulated Alternating Current at 3 Carrier Frequencies

“…The 2 stimulators that generated the same phase charge per waveform, either a 200-microsecond (phase duration) sine wave or a 200-microsecond (phase duration) symmetrical biphasic rectangular wave, produced the same electrically induced maximum quadriceps torque (%MVIC) (P Ͼ.05); but both stimulators produced significantly greater %MVICs (PϽ.05) than a stimulator that generated a 125-microsecond (phase duration) sine wave. 13 Similarly, in our study, the waveforms with the most charge produced the greatest quadriceps muscle force at equivalent current intensities.…”

“…In support of this interpretation, Ward and Shkuratova 15 reported that the current amplitudes required to produce 60% of the maximum wrist and finger flexor EIT decreased at lower carrier frequencies. In addition, Snyder-Mackler et al 13 compared the quadriceps torque generating ability of 3 different electrical stimulators. Each stimulator produced a different waveform.…”

“…The results of these last 2 studies, [13][14] which examined a carrier frequency range from 1000 to 15 000 Hz, suggest that when using burst-modulated alternating current, a lower carrier frequency with a longer phase duration may increase the size of the EIT and decrease the current amplitude required to produce the highest EIT response. The relationship between current frequency, phase duration, and phase charge provides the rationale for the larger electrically induced muscle torques measured at the lower carrier frequencies in these studies.…”

“…The results of this study indicated that the current amplitudes required to produce the 3 tested motor responses increased with increasing carrier frequencies. While using the maximum current amplitude tolerated by each research participant, Snyder-Mackler et al 13 compared the maximum EITs produced by 3 different electrical stimulators: an electrical stimulator that delivered a 2500-Hz alternating current (phase duration, 200 microseconds), a stimulator that delivered a 4000-Hz alternating current (phase duration, 125 microseconds), and a low-frequency stimulator that delivered a symmetrical biphasic rectangular wave at 50 Hz (phase duration, 200 microseconds). The results demonstrated that when the quadriceps femoris muscle group was stimulated with the 4000-Hz alternating current, it produced significantly less force than when stimulated with the 2500-Hz alternating current (P Ͻ .01) or the symmetrical rectangular pulsed current (P Ͻ.05).…”

Efeitos da diatermia por ondas curtas no torque do músculo quadríceps femoral durante a estimulação elétrica neuromuscular e contração voluntária em indivíduos saudáveis

“…The trunk was also stabilized with belts in order to avoid possible muscular compensations. The dynamometer was programed at angle velocity of 0° per second (isometric mode), and the knee joint of the dominant leg was positioned at 60º of flexion, and the dynamometer's arm rest was placed on the distal region of the volunteer's leg, which allowed a complete dorsiflexion arch 12,[21][22][23] . During the tests 1 and 2, the volunteers were verbally encouraged by the examiner to perform the highest strength as possible.…”