Which waveform type is generally avoided for muscle contraction in NMES?

• A. Biphasic symmetric pulses
• B. Biphasic asymmetric pulses
• C. Burst-modulated (Russian) currents
• D. Monophasic or DC

Answer: (D)

In NMES, the goal is to produce a muscle contraction with stimulation that stays safe and comfortable by keeping the net charge at the electrode interface balanced. Monophasic or direct current would deliver a constant polarity, which drives continuous electrochemical reactions at the skin and tissue. This leads to harmful pH shifts, gas formation, skin irritation or burns, and unpredictable nerve activation. Because of these risks, direct current is avoided in NMES.

Instead, charge-balanced waveforms are used so there’s no net DC over time. Biphasic symmetric or asymmetric pulses, and burst-modulated currents, deliver pulses that alternate polarity or cancel out the overall charge, enabling effective muscle contraction while reducing the chance of tissue damage or irritation.