Transcutaneous Electrical Nerve Stimulation (TENS ) units are small, battery-powered devices used for chronic pain treatment that produce a vibration or signal intended to interrupt pain transmissions from nerves before they reach the brain. The TENS machine can be worn outside and attached to your body via electrodes with sticky patches, or a surgeon can actually implant the electrodes under the skin. When TENS units (or electrical stimulators) are implanted, they are operated with small controls that send signals through the skin into the muscles. TENS is considered to be the electrical equivalent of portable acupuncture or acupressure. There are two theories practitioners use to explain how TENS works. The first is the gate control theory that says nerves can carry only one signal at a time, and the TENS signal overrides the pain signal, in effect closing the gate on pain transmissions before they can reach the brain. The second theory is the endorphin theory that claims TENS stimulates the body’s production of these natural painkillers, giving users relief. TENS use falls into a treatment category called “hyperstimulation analgesia.” These treatments include vibration, acupressure, acupuncture, and massage. Their effectiveness as pain relievers varies among individuals, working reasonably well for some people and less so for others. Researchers have found that the conditions most likely to get a long-term benefit from TENS include failed back syndrome, reflex sympathetic dystrophy, multiple sclerosis, peripheral vascular disease, and peripheral neuropathy. This blog post is an excerpt from A Day Without Pain (Revised) by Mel Pohl, MD, FASAM; Published by Central Recovery Press (CRP).