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What are TENS Units?

Mary McMahon
Updated Feb 23, 2024
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A Transcutaneous Electrical Nerve Stimulation (TENS) unit is a medical device which is used to treat pain by acting to block pain signals to the brain, or to trigger the production of endorphins, depending on how it is used. Several studies have been conducted with patients who use TENS units, and the effectiveness is a subject of debate. Some patients certainly benefit from the use of a TENS unit, while others apparently feel nothing. TENS units should be used under medical supervision, as improper use of the devices can be dangerous.

To use TENS units, small electrode pads attached to leads are placed at the site of the pain with at least one inch (2.5 centimeters) between them. The TENS unit is turned on, generating a small electrical shock which stimulates the nerves in the area. The intensity, frequency, and duration of the shock can be controlled at the base TENS unit, which can be designed to be worn through the day or be a bulkier device for use in a medical office. Studies have suggested that at a high frequency, TENS units block pain signals to the brain, while lower frequencies may stimulate the creation of endorphins. The use of a TENS unit is accompanied with a mild tingling sensation, but should not involve muscle contraction.

Because TENS units use electrical current, proper supervision is needed to learn how to use one safely. People with internal electrical devices such as pacemakers should not use TENS units at all, and other patients should work with a physician to learn how, where, and when to use a TENS unit. The electrodes should never be placed around the eyes, nose, or mouth, or mounted on either side of the skull. TENS units are also not designed for internal use, such as the inside of the mouth. With proper training, a TENS unit may help to relieve pain, and help patients to use less analgesics. When purchasing TENS units, make sure to buy devices approved by government agencies which regulate medical devices, such as the United States Food and Drug Administration.

An Electronic Muscle Stimulator (EMS) is a similar device, but it is designed for a different purpose; it stimulates the muscles, rather than the nerves, with more electricity. Originally, EMS units were used to treat muscle atrophy by gently contracting and releasing muscles, and were sometimes included in physical therapy and recovery programs. They have also been adopted, however, by physical fitness companies, who claim that using an EMS unit can tone and tighten the muscles while reducing body fat. An EMS unit will certainly contribute to muscle tone, but it will probably not live up to any of the other claims on the packaging, and can also be highly dangerous when used improperly.

WiseGeek is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a WiseGeek researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Mary McMahon

Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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