For a patient with fair quadriceps strength and intact sensation, which electrical stimulation parameter would best promote muscle strengthening?

• A. Frequency of 35 pps, duration of 50 microseconds
• B. Frequency of 35 pps, duration of 150 microseconds
• C. Frequency of 50 pps, duration of 250 microseconds
• D. Frequency of 150 pps, duration of 50 microseconds

Answer: (C)

For strengthening with electrical stimulation, you want a strong, fused, tetanic contraction without causing excessive fatigue. That’s best achieved by using a moderate frequency around 50 Hz to produce tetany, and a longer pulse width in the 200–300 microsecond range to recruit more motor units efficiently. The combination of 50 pps and 250 microseconds fits this well, giving a robust contraction that's effective for strengthening while staying tolerable.

The other options either don’t reach tetany (too low a frequency) or don’t recruit enough fibers (too short a pulse width), or risk fatigue from very high frequency paired with a short pulse width.