Stimulus duration is:

• A. The rate at which pulses occur
• B. The percentage of time the current is on
• C. The energy per second delivered
• D. The time length of each stimulus, such as seconds, milliseconds, or microseconds (also called pulse width)

Answer: (D)

Stimulus duration is how long a single electrical pulse lasts. This is the pulse width, measured in seconds, milliseconds, or microseconds. It determines the amount of charge delivered in each pulse and influences which nerve fibers are activated; shorter durations deliver less charge per pulse, while longer durations deliver more.

The rate at which pulses occur is the frequency—how many pulses happen each second. The energy delivered per second is a function of both the pulse duration and how often pulses occur (and the amplitude), so it’s about the overall power/energy rate, not just the duration itself. The percentage of time the current is on is the duty cycle, which describes on-time relative to the total cycle and depends on both duration and frequency.