Until recently, TENS (Transcutaneous Electrical Nerve Stimulation) has been available only as an expensive prescription therapy for temporary relief of all kinds of pain - including the debilitating lower back pain associated with sore and aching muscles. TENS is gentle, noninvasive, no addictive yet very effective painkiller with none of effects or concerns linked to drug medications. How TENS Works. It is believed TENS works via two mechanisms: It may close the nervous system gates through which pain signals travel to the brain; and it may activate the release of endorphins, the body's natural mechanism for suppressing pain.