Acupuncture-like TENS uses which settings and mechanism?

• A. Frequency 100-200 Hz with long pulse 500-1000 μs; analgesia via GABA.
• B. Frequency 50-100 Hz; short pulse 50-100 μs; immediate relief only.
• C. Frequency 2-10 Hz and longer pulse duration 200-500 μs; analgesia mediated by endogenous opioids; relief may last longer after stimulation.
• D. Frequency 1 Hz with pulse 2000 μs; non-opioid mechanism.

Answer: (C)

Acupuncture-like TENS relies on engaging the body's own pain-control system rather than just blocking pain signals at the spinal cord. The key settings are a low frequency, about 2–10 Hz, paired with a longer pulse duration, around 200–500 microseconds. This pattern preferentially activates pathways that trigger the release of endogenous opioids—endorphins and enkephalins—in the spinal cord and brain, which then bind to mu-opioid receptors and enhance descending inhibitory pathways. Because this opioid-mediated analgesia can persist after the stimulation ends, the relief may last longer than the stimulation itself. In contrast, higher-frequency, shorter-duration TENS tends to produce faster but shorter relief mainly through gate-control mechanisms and is not primarily opioid-mediated.