Conventional (high-rate) TENS settings typically include:

• A. Frequency 50-100 Hz; pulse duration 50-100 μs; amplitude comfortable; treatment 15-60 minutes.
• B. Frequency 2-4 Hz; pulse duration 200-500 μs; amplitude high; 30 minutes.
• C. Frequency 100-200 Hz; pulse duration 500-1000 μs; amplitude high.
• D. Frequency 10-20 Hz; pulse duration 100-200 μs; amplitude comfortable; 10 minutes.

Answer: (A)

High-rate (conventional) TENS aims to provide quick, comfortable pain relief by stimulating large-diameter sensory fibers at a high frequency. The high frequency, typically around 50–100 Hz, combined with a very short pulse duration (about 50–100 microseconds) activates the gate-control mechanism in the spinal cord, which dampens pain signals before they reach the brain. Because the pulses are so brief, you get sensory tingling without triggering muscle contractions, so the amplitude should be at a comfortable sensory level. Treating for about 15–60 minutes is standard to achieve meaningful analgesia while avoiding rapid adaptation.

The option that matches this pattern—50–100 Hz, 50–100 μs pulse duration, comfortable amplitude, and 15–60 minutes—best reflects conventional high-rate TENS. Other parameter sets describe different modes, such as low-rate TENS (which uses lower frequency and longer pulse widths and may involve higher amplitudes and motor responses) or configurations that are not typical for conventional high-rate therapy.