Stimulus frequency is measured in:

• A. Milliseconds
• B. Percent duty cycle
• C. Cycles per second or Hz
• D. Amperes

Answer: (C)

Frequency is about how often a repeating signal completes one full cycle each second. In electrotherapy, the stimulus is a repeating waveform, so its frequency tells you how many cycles occur per second. The standard unit is cycles per second, also called hertz (Hz). If a waveform repeats 20 times every second, its frequency is 20 Hz. The inverse, the period, is the time for one complete cycle (period = 1/f). As frequency goes up, each cycle becomes shorter in time.

Milliseconds, on the other hand, measure a time interval such as pulse width or the time between pulses, not how often cycles repeat. Percent duty cycle describes how much of each cycle the signal is on (on-time divided by the total cycle time), not the repetition rate. Amperes measure current, not frequency.