When does polarity not matter?

• A. When energy is low
• B. When using symmetric biphasic current
• C. When the electrodes are the same size
• D. When the treatment is very short

Answer: (B)

Polarity doesn’t matter when the current is symmetric biphasic. In this waveform, each pulse has equal positive and negative phases that are opposite in polarity and of the same magnitude and duration, so the total charge delivered over every cycle sums to zero. Because the stimulation is charge-balanced, swapping which electrode is positive and which is negative produces essentially the same effect on nerves and tissues—the tissue doesn’t accumulate net charge in one direction. This contrasts with monophasic or asymmetric waveforms, where one electrode would deliver a net charge and the response can depend on which side is the anode or cathode.

Other factors like energy level, electrode size, or short treatment time don’t by themselves guarantee polarity independence. They can influence comfort, current density, and threshold effects, but the key idea is the balanced, bidirectional nature of symmetric biphasic stimulation that makes polarity inconsequential.