Larger muscles require a longer pulse duration (PD) to recruit motor units.

• A. Larger muscles require shorter pulse durations.
• B. Larger muscles require longer pulse durations.
• C. Pulse duration does not affect recruitment.
• D. Pulse duration should be avoided for larger muscles.

Answer: (B)

Longer pulse duration provides more charge per pulse, which helps depolarize more nerve fibers and recruit more motor units. In larger muscles, there are more motor units and fibers deeper under the skin, and they face greater impedance. Delivering a longer pulse increases the total charge delivered at a given current, making it easier to reach the thresholds of these deeper or higher-threshold units and produce a stronger contraction. That’s why extending the pulse duration is often needed for larger muscles to achieve effective recruitment. While increasing pulse duration can raise discomfort, the goal is to use enough duration to recruit the desired motor units while balancing comfort. Shorter pulse durations deliver less charge and typically recruit fewer motor units in a large muscle, and pulse duration does affect recruitment, so it shouldn’t be avoided when you’re trying to energize a larger muscle group.