High-frequency TENS engages which pain modulation mechanism?

• A. Endorphin release
• B. Gate control theory via mechanoreceptor stimulation
• C. Muscle spasm reduction
• D. Increased blood flow

Answer: (B)

High-frequency TENS reduces pain by engaging the gate control mechanism through stimulation of large-diameter mechanoreceptors (A-beta fibers). This non-painful input activates inhibitory interneurons in the spinal cord's dorsal horn, effectively “closing the gate” to nociceptive signals from C and A-delta fibers so fewer pain impulses reach the brain. The analgesia from this mechanism is typically immediate and short-lived, matching the high-frequency modality. Endorphin release, on the other hand, is more associated with low-frequency TENS and endogenous opioid pathways, producing a different, longer-lasting type of relief. Muscle spasm reduction and increased blood flow can accompany analgesia but are not the primary mechanism by which high-frequency TENS achieves pain modulation.