Effect of rectangular and exponentially climbing waveforms on knee extension torque during neuromuscular electrical stimulation

BACKGROUND: Electrical stimulation is shown to be effective for the amelioration of paralysis. The stimulation pattern can have a direct relation to injected charge in the stimulated area resulting in a wider area stimulation and consequently better recovery. OBJECTIVE: In this study, we investigated the effect of two electrical stimulation waveforms, rectangular and exponentially climbing. Three parameters of current, voltage, and knee extension torque of the 2 waveforms were recorded and used for the comparison of the two waveforms. METHODS: Fifteen male and 15 female able-bodied subjects (age: 25.0 ± 3.2) were recruited. Electrical stimulation was applied to right quadriceps muscles. At the maximum tolerable intensity, the 3 parameters were recorded for each of the 2 waveforms. Using the recorded knee extension torques, the adjusted maximum electrically induced contraction to voluntary torques in percent (%MEIC) of the two waveforms were calculated. Together with the other two parameters, current and voltage, the 2 waveforms were compared. RESULTS: The %MEIC and maximum voltage were significantly higher with the exponentially climbing waveform than with the rectangular waveform (%MEIC:p <0.05, max voltage:p <0.01). The maximum current did not differ significantly between conditions. CONCLUSION: These results indicate that an exponentially climbing waveform may induce stronger torque than a rectangular waveform and might thus be useful when applying NMES in clinical situations.