TENS (Transcutaneous Electrical Nerve Stimulation) analgesic action is chemically mediated by neural processes of pain perception. Electrical impulses sent by the use of surface electrodes stimulate A-beta sensory nerve fibers of large diameter in the skin. The gate control theory proposes that the release of these fibers will suppress the transmission of the signals of pain through smaller A-delta and C fibers at the spinal cord level, which actually closes the gate and makes the pain perception less effective. This is not the only effect of low-frequency TENS because it can activate the central nervous system to produce endogenous opioids like endorphins and enkephalins. These are natural analgesic chemicals, which attach to opioid receptors in the spinal cord and the brain and produce more lasting analgesia. Additionally, TENS has the potential to improve local blood supply and have an indirect effect of decreasing muscle spasm to provide a more conducive tissue healing and functional recovery. In general, the pathophysiological mechanisms of TENS are both peripheral and central and cause effective pain modulation without necessarily causing muscle contraction.