To strengthen wrist extensors with NMES, which parameter set is appropriate?

• A. Frequency 15–25 Hz; Pulse duration 100–150 µs; Ramp 0.5 s; On-time 2–4 s; Off-time 10–20 s; Amplitude high but tolerable.
• B. Frequency 35–50 Hz; Pulse duration 200–300 µs; Ramp 1–2 s; On-time 6–10 s; Off-time 20–40 s; Amplitude strong but comfortable.
• C. Frequency 60–80 Hz; Pulse duration 400–600 µs; Ramp 3 s; On-time 8–12 s; Off-time 10–20 s
• D. Frequency 2–5 Hz; Pulse duration 20–50 µs; Ramp 0 s; On-time 1 s; Off-time 2 s

Answer: (B)

For strengthening the wrist extensors with NMES, you want parameters that produce a solid, tetanic contraction while giving the muscle enough time to recover between bursts. This means using a moderate-to-high frequency for a smooth, sustained contraction, a pulse duration long enough to recruit the relevant motor fibers, a gradual ramp to reduce discomfort, and a work–rest pattern that supports durable strengthening.

The frequency range in the chosen set (35–50 Hz) is ideal for eliciting tetanic contractions rather than simple twitches, which is important for building strength. The pulse duration (200–300 µs) is sufficient to recruit larger wrist-extensor fibers without causing excessive current or discomfort. A ramp of 1–2 seconds helps the patient tolerate the onset of contraction. The on-time of 6–10 seconds provides enough contraction time to recruit muscle fibers effectively, and the off-time of 20–40 seconds gives adequate recovery to minimize fatigue. Finally, aiming for an amplitude that is strong but comfortable ensures a meaningful contraction without causing pain or withdrawal.

The other options either use too low a frequency, which yields weaker contractions, or too long a on-time/off-time mismatches that increase fatigue or reduce effectiveness, or too short a pulse duration that may not recruit the needed fibers.