Transcutaneous electrical nerve stimulation (TENS units) uses electric current produced to stimulate the nerves for therapeutic purposes. The unit is usually connected to the skin using two or more electrodes. A typical battery-operated TENS unit is able to modulate pulse width, frequency and intensity.
TENS is a non-invasive, safe treatment that has been used to reduce musculoskeletal pain, both acute and chronic. While controversy exists as to its effectiveness in the treatment of chronic pain, several systematic reviews or meta-analyses indicate its effectiveness for postoperative pain, osteoarthritis, and chronic musculoskeletal conditions. In general, electrical stimulation is probably best utilized in conjunction with other treatment strategies (i.e. therapeutic exercise, manual therapies, anti-inflammatory and pain medications, injection therapy, lifestyle changes, etc.) and is less effective when used as the primary treatment. Home units are relatively affordable, easy to operate, and are very portable.
Scientific studies suggest that TENS units work by blocking the transmission of pain signals to the brain as outlined by the Gate Theory which was first described by Melzack and Wall in 1965. Decreased pain occurs during use and the therapeutic effect may last for minutes to a couple hours after treatment. Some companies report that electrical current helps to promote healing of damaged tissues which reduces chronic pain. However, this has not been proven scientifically. Before using a TENS unit you should always consult your physician as there are certain situations for which treatment with electrical stimulation is contraindicated (e.g. someone with a pacemaker or defibrillator, over areas of tumor/malignancy, and directly over the spinal column in a patient with a prior laminectomy).