Figure 13. Propagating AP due to an optimal (rectangular) waveform,  = 100 : For the shortest durations, the plain rectangular waveform outperforms by the ones associated to the linear-ramp voltage profile.

One can see clearly that the steep rise of the waveform yields an early superlinear ramping of the membrane voltage. However, the rectangular waveform requires a lot more charge to be transferred (see Fig. 10).