What is the duty cycle and why is it important in NMES programming?

• A. The on-time divided by the total cycle (on plus off); it controls fatigue and recovery
• B. The carrier frequency of the current
• C. The electrode size
• D. The amount of gel used

Answer: (A)

The duty cycle is the fraction of each stimulation cycle that the current is actually on, i.e., the on-time divided by the total cycle time (on plus off). It’s usually expressed as a percentage. This matters in NMES because it governs how long the muscle is contracting before it has a rest period. A higher duty cycle means the muscle spends more time in contraction with less recovery, which increases fatigue quickly. A lower duty cycle provides more recovery between contractions, reducing fatigue and allowing longer sessions or greater overall work.

For example, if you have 5 seconds of stimulation (on) and 25 seconds of rest (off), the duty cycle is 5/(5+25) = 16.7%. The goal is to choose a duty cycle that yields the needed torque without causing rapid fatigue, taking patient tolerance into account.

The other factors listed—carrier frequency, electrode size, and gel amount—are not duty cycle; frequency relates to how fast each pulse repeats, while electrode size and gel affect comfort and current delivery, not the on/off timing.