For generating a motor response, the stimulation frequency is typically

• A. Lower
• B. Moderate
• C. Higher
• D. Variable

Answer: (C)

Stimulation frequency determines whether the muscle response is a series of separate twitches or a fused, smooth contraction. To reliably generate a motor response, you want a fused tetanic contraction, which happens when pulses come in quickly enough that individual twitches summate in time. That requires a higher frequency. Lower frequencies produce discrete, visible twitches with pauses in between, which doesn’t create a steady motor action. A moderate or variable rate won’t consistently produce the sustained contraction clinicians aim for, so a higher frequency is used to achieve the desired motor response (typical therapeutic NMES ranges around tens of hertz).