Duty cycle is the ratio of on-time to the total cycle.

• A. The ratio of on-time to total cycle.
• B. The duration of each pulse.
• C. The amplitude.
• D. The frequency.

Answer: (A)

Duty cycle is about how much of each treatment cycle the device is delivering current. It is defined as the on-time divided by the total cycle time, often expressed as a percentage. For example, if the current is on for 2 milliseconds out of a 10 millisecond cycle, the duty cycle is 2/10, or 20%. This is different from how long a single pulse lasts (pulse width), which is just the absolute length of time the current is on during one pulse. Amplitude refers to how strong the current is, and frequency refers to how many cycles occur each second. A higher duty cycle means more time delivering current within each cycle, more total charge, and potentially more heating or stronger muscle effects, which is why controlling duty cycle is important in electrotherapy.