Neuromuscular electrical stimulation can be used to increase strength of skeletal muscle. In neuromuscular electrical stimulation of innervated skeletal muscle, the application of the highest possible intensities of electricity is an important determinant of therapeutic success with regard to strength training. The therapeutic goal of "strengthening muscles" is opposed to the side effect of discomfort through the application of electricity. The aim of the present study was to compare three forms of electric current with respect to subjective tolerance and maximum achievable muscular strength. Twenty-nine healthy male volunteers were included in a single-blind study in which three forms of electric current were applied in a randomized fashion. The following types were compared: a short monophasic form, a biphasic form that was twice as long in terms of impulse duration, and a long monophasic form with an equal impulse duration than tht of the biphasic form and with an impulse form that corresponded to the short monophasic current. Stimulation was administered via surface electrodes placed on the knee extensors in the lower extremity on the right side. The intensity of the current was increased to the individual limit of tolerance or to a maximum of 100 mA. The main target parameter used to determine the success of treatment was the maximum electrically induced strength as a percentage of maximal voluntary contraction. The short monophasic form of electricity was associated with much less discomfort than the long monophasic and biphasic forms (p < 0.0001, p = 0.0062). Furthermore, the biphasic form was better tolerated (and therefore had a larger therapeutic range of application) than the long monophasic form (p = 0.041). The biphasic and long monophasic forms produced higher values for maximum electrically induced strength than did the short monophasic form (p = 0.0001, p = 0.0010). To summarize: the biphasic form had a larger range of therapeutic application than the long monophasic form. Furthermore, the biphasic form produced 40% more electrically induced strength than the short monophasic one. It may be concluded that, in terms of therapeutic application, the biphasic form of electric current is superior to the monophasic forms described in the present study.