Why does functional electrical stimulation (FES) typically use a lower frequency (35-50 pps)?

• A. To maximize fatigue
• B. To reduce fatigue
• C. To minimize fatigue
• D. To increase fatigue

Answer: (C)

Frequency choice in functional electrical stimulation determines how the muscle responds over time. Using a lower to moderate rate, like 35-50 pulses per second, you can produce a smooth, sustained contraction (a tetanus) without driving the muscle into rapid fatigue. At higher rates, the contraction may be stronger initially but the metabolic demand is greater and fatigue accumulates faster, making it harder to keep the contraction going for functional tasks. At too low a rate, you get visible twitches rather than a steady, functional contraction. So 35-50 pps hits a balance, giving a usable, smooth contraction while minimizing fatigue during the activity.