What frequency range is generally used to achieve tetanic contractions in NMES for strengthening?

• A. 5–10 Hz
• B. 30–50 Hz
• C. 70–90 Hz
• D. 15–25 Hz

Answer: (B)

Achieving a smooth, sustained contraction in NMES for strengthening depends on firing enough pulses per second so the muscle twitches fuse into a tetanus. If the rate is too low, you’ll see separate twitches rather than a continuous contraction; if it’s too high, the contraction can become very fatiguing and uncomfortable. The practical range used to produce a strong, tetanic contraction without excessive fatigue is about 30–50 Hz. Within this window you get a solid, controlled contraction suitable for strengthening. Frequencies at the lower end (5–10 Hz) don’t produce a true tetanus, and those at the higher end (70–90 Hz) increase fatigue and discomfort without added benefit for most NMES strengthening protocols.