Transcutaneous electrical nerve stimulation (TENS) is a drug-free pain management technique that applies small amounts of electricity to nerve endings beneath the skin. It is sometimes used to treat a wide range of conditions, including pelvic pain, neuropathy, arthritis, back pain, shoulder pain and other types of joint pain, muscle pain and post-surgical pain.

Scientists are unsure how TENS may relieve pain. One theory is that the device blocks pain impulses. Pain results from an interaction between several components of the nervous system, including the peripheral nerves, spinal cord and brain. Pain in a particular part of the body is sensed by the peripheral nerves and transported to the brain through the spinal cord. It is believed that certain signals facilitate the transmission and others inhibit it.  When TENS unit is used appropriately, the stimulus it provides inhibits pain transmission to the brain.  However, when the intensity of the TENS stimulation is too strong it can facilitate transmission of the pain signals and result in pain.

Other theories suggest that the electrical impulses delivered to brain during TENS treatment may increase levels of chemicals in the brain that relieve pain, such as endorphins. Still other theories suggest that electrical stimulation such as that delivered by TENS may:

• Inhibit overactive nerves
  
  
• Restore disturbed neuronal pathways
  
  
• Improve blood flow
  
  
• Strengthen muscles
  
  
• Numb the painful area

Research on the effectiveness of TENS is continuing. Some studies have shown no benefit, but others have found it to be a useful part of pain management. Many individuals report success with TENS, but for some it has little or no effect. In some cases, it may be used as an alternative or adjunct to the use of powerful pain medications such as opioids because TENS has few side effects and is not addictive. When TENS does help an individual, improvement may be apparent immediately or within three or four months of use, according to the National Institutes of Health.

TENS may be used in outpatient settings such as rehabilitation centers, healthcare clinics or medical offices. It is usually applied by a physician, physical therapist, chiropractor or other healthcare professional who has had special training, such as an occupational therapist.

Patients who respond to TENS in therapy can be trained to use it at home. Patients can rent or buy the device. The purchase price varies widely, but the unit usually costs several hundred dollars. If a physician has prescribed TENS, insurance may pay for the device.  The only parts that need to be replaced regularly are the electrodes that attach to the skin.

A typical TENS unit is usually smaller than a cell phone and has a clip so the unit can be worn on a belt. The device consists of a power module, generally powered by a 9-volt battery and attached by wires to self-adhesive cloth or foam pads called electrodes.

The electrodes are placed on the skin to supply current to the nerves just below the surface of the skin. The wires are usually run under the patient’s clothes so they are not noticeable. Controls on the power unit allow adjustments to the electrical stimulation. There are also smaller wireless devices that weigh less than half an ounce and attach directly to the electrodes.

The TENS unit can be adjusted according to:

• Intensity (amplitude). Strength of the electrical current.
  
  
• Frequency (pulse rate). The number of waves per second. Types include continuous flow and bursts of current.
  
  
• Duration (pulse width). Given in microseconds.

Trial and error is often the best way to determine how TENS works best for an individual. The patient may experiment with various frequencies, intensities and electrode locations, within guidelines set by a physician or other healthcare provider.