Figure 1.

Biphasic rectangular pulse. This means that there are two phases with charge delivery. The first phase is the cathodic (negative) one (A), after that there is a delay (B). The anodic (positive) phase follows (C), which has the same charge as the cathodic one, but with a positive charge instead of a negative. In this way the charge remains balanced. The last phase is the resting phase (D). The duration of it determines the frequency of the stimulus. A longer duration of phase D implies less pulses per second (pps) and thus a lower stimulus frequency. The shape of all the phases are rectangular and a current is delivered, instead of a voltage.