What frequency and pulse duration ranges are commonly used for NMES muscle strengthening?

• A. Frequency 35-80 Hz; pulse duration 150-350 μs; amplitude to elicit visible contraction; ramp 1-2 s.
• B. Frequency 1-5 Hz; pulse duration 100-200 μs.
• C. Frequency 100-120 Hz; pulse duration 1000 μs.
• D. Frequency 5-15 Hz; pulse duration 50-100 μs.

Answer: (A)

Producing a fused, stepped-up contraction is the goal of NMES for strengthening, so the frequency and pulse duration are chosen to recruit motor units efficiently without causing excessive fatigue or discomfort. A frequency in the mid-to-high tens range, around 35–80 Hz, keeps motor units firing rapidly enough to create a smooth, tetanic contraction rather than separate twitches. The pulse duration, about 150–350 microseconds, is long enough to recruit motor fibers effectively but not so long that it increases fatigue or discomfort. Set the amplitude to produce a visible contraction so you’re sure the muscle is being engaged, and use a ramp of about 1–2 seconds to gradually reach the target intensity, improving tolerance and reducing an abrupt or uncomfortable onset of contraction. Frequencies and pulse durations outside this range tend to produce incomplete contractions (very low frequencies) or excessive fatigue and discomfort (very high frequencies with long pulses).