A comparison of torque generating capabilities of three different electrical stimulating currents.

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 (%MVIT).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. J Orthop Sports Phys Ther 1989;10(8):297-301.