How is duty cycle defined in NMES, and what is a typical strengthening setting?

• A. Duty cycle is the on-time divided by the sum of on-time and off-time; typical is on 6–10 seconds, off 14–40 seconds
• B. Duty cycle is the ratio of off-time to on-time; typical is 1:1
• C. Duty cycle is the on-time divided by off-time; typical is 1:2
• D. Duty cycle is the off-time divided by the sum of on-time and off-time; typical is 2:1

Answer: (A)

Duty cycle in NMES is the fraction of each cycle during which the current is on. It is defined as on-time divided by the total cycle time (on-time plus off-time). For example, if you have 6 seconds on and 14 seconds off, the cycle lasts 20 seconds and the duty cycle is 6/20 = 0.30 (30%).

For strengthening, you want enough time off between contractions to reduce fatigue while still producing strong, tetanic contractions. That’s why a typical strengthening setting uses on-time of about 6–10 seconds with off-time of about 14–40 seconds. This yields a relatively modest duty cycle (roughly 20–30%), balancing stimulus and recovery to promote strength gains without excessive fatigue.

The other definitions are incorrect because they either treat the ratio as off-time over on-time or off-time over the total, which does not match how the duty cycle is used in NMES practice.