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9 Facts: What is a TENS Unit?

Published October 19, 2017
| Written By SpineNation Editorial Staff   | Medically Reviewed by Jerry Nichols, MD
A transcutaneous electrical nerve stimulation (TENS) unit is a device that relieves pain by sending small electrical currents into specific parts of the body.

Some TENS units are designed to be used in a hospital or doctor’s office. Others are portable and can be used at home or even worn under the clothing.

What is TENS therapy?

Dr. Michael D. Detten, a physical therapist and clinic director at Physical Therapy Central’s Oklahoma City Southwest location, says transcutaneous electrical nerve stimulation (TENS) is one of several types of electrical stimulation used for pain relief or other benefits.

Other ones include interferential current therapy (IFC) and neuromuscular electrical stimulation (NMES). Detten mainly uses IFC in his practice.

During TENS therapy, an electrical current is applied using a device known as a TENS unit. Wires from the device are attached to self-adhesive electrode pads placed on the skin. Electrical current in the wires flows through the skin and into the area of the body near the electrode.

Scientists are not certain how TENS relieves pain. Currently, they think that the electrical stimulation affects nerve signals flowing from the body to the brain or spinal cord. It may also cause the local release of chemicals in the body that control pain.

What types of pain does TENS relieve?

TENS therapy can be used for both short-term (acute) and long-term (chronic) pain, including:
  • headaches
  • back and neck pain
  • pain after surgery
  • joint pain
  • pain due to a muscle strain
  • pain caused by arthritis, tendonitis, or other medical conditions
It may also be a good option when other treatments aren’t possible.

“TENS can be a great tool to use when patients have high levels of pain and are not tolerating hands-on therapy and exercise due to pain,” says Dr. Nina Geromel, a physical therapist and owner of Geromove Physical Therapy in Milwaukee, Wisconsin.

How do you use a TENS unit?

A TENS unit has controls that allow the user to adjust the electrical current to provide the right amount of pain relief. This includes changing the following aspects of the electrical current:
  • Intensity: How much electrical current flows into the body.
  • Frequency: The number of pulses of electrical current per second.
  • Duration: How long the electrical current is applied during each pulse.
  • Pattern: Whether the electrical current is applied in steady pulses or variable pulses.

Sessions with a TENS unit vary in length, from a few minutes at a time to 15 to 30 minutes. Some types of TENS can be administered as often as needed.

Detten says electrical stimulation sessions longer than 15 minutes don’t usually yield additional benefits. In the clinic, though, this is long enough to provide a “window of opportunity” — increasing the flexibility and mobility of the parts of the body being treated.

“This allows the patient to perform prescribed exercises and movements in an active way without as much pain and discomfort,” says Detten.

Similarly, Geromel says she typically uses TENS in the clinic for only 10 to 15 minutes at a time, mainly to reduce a client’s pain so she can use other therapies.

“When I do use TENS in the clinic, it is typically for a short period of time just to decrease pain acutely,” says Geromel. “This is to allow me to get into other interventions that are better at creating long term relief, such as hands-on therapy and exercise.”

How long does the pain relief last?

Studies have found that pain relief from TENS can last for up to 24 four hours after treatment, but it is often much less.

“TENS can feel really good while the unit is on the muscle and working,” says Geromel, “but is not so effective for long-term relief.”

This is because while the TENS unit is on, it stimulates the nerves to block the pain signals. “Once that stimulation is removed, the pain returns to normal,” says Geromel. “This is true for all types and causes of pain.”

Some people may also develop a tolerance to TENS, which means they will have less pain relief than when they started. This is more likely to happen if they use a TENS unit frequently or use the same frequency and intensity each time.

The risk of tolerance can be reduced by taking a longer break between sessions or changing the type of electrical stimulation used.

Can you use a TENS unit at home?

Home-based TENS units are available, including ones small enough that they can be attached to your belt or worn under your clothing.

Detten says some patients may benefit from a home TENS unit, although it depends on the cause of their pain as well as their long-term goals. They may also need to work with a health provider first in order to get the most out of their TENS unit.

“We spend time with patients and educate them on how to appropriately use the units in a safe manner,” says Detten, “so they can continue with this temporary pain relief treatment at home.”

Geromel cautions people against relying on TENS as their sole pain relief strategy. Instead, they should think of it as providing enough short-term relief that they can do other home-based therapies, such as stretching or exercises.

In some cases, though, TENS can help people get through a particularly painful episode.

“If a patient is dealing with chronic pain, I may recommend a TENS unit at home for more emergency situations where their pain is preventing them from functioning during the day,” she says. “Patients can even wear the unit while doing other activities.”

Are there side effects of TENS?

TENS therapy is safe for most people to use and has few side effects. However, the electrical current produced by a TENS unit can cause a tingling or buzzing sensation that some people may find uncomfortable.

Some people may also develop skin irritation or have an allergic reaction to the electrode pads. The risk of irritation can be reduced by changing the position of the pads or waiting longer between TENS sessions. Hypoallergenic pads are also be available for people who are sensitive.

When to avoid TENS

Although TENS therapy is generally safe, some people should avoid its use, including:
  • Pregnant women (except for treating low back pain)
  • People with uncontrolled epilepsy
  • People with an artificial cardiac pacemaker or implantable cardioverter-defibrillators (ICDs) should avoid applying TENS to the chest.

People with ongoing medical conditions should check with their doctor before using a TENS unit.

In addition, electrodes should not be placed on the head, front of the neck or directly over the spine. Electrodes should also not be placed over broken skin or a tumor.

Is TENS effective?

Many studies have looked at whether TENS therapy works for pain relief, with mixed results.

Some research has found that TENS can reduce the intensity of acute pain, including after surgery. Other studies, though, have found that TENS may not work for pain during labor.

Research also shows that TENS can relieve chronic musculoskeletal pain or pain due to knee osteoarthritis. However, many studies looking at chronic pain have been of poor quality.

More research is needed to know how much TENS helps and which people would benefit most.

Why use TENS?

Although more research on TENS is needed, this treatment offers many benefits that make it an attractive type of pain relief.

It is noninvasive, requiring no injections. It also has fewer side effects than many pain medications, some of which can damage the liver or carry a risk of addiction, especially with long-term use.

TENS units are also portable, so can be used at home or worn under the clothing. This is useful for people with chronic pain and even those recovering from an injury or surgery.

“Electrical stimulation has been proven to be effective in combination with active treatment strategies,” says Detten. “We know the cost of this treatment to be low, the risks minimal, and most importantly a non-addictive intervention compared to opioid utilization for treating pain.”

Diagram shows different electrode points on human body.Photo Credit: https://www.tensunits.com/CHART.html

Updated: May 13, 2020

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Contributors and Experts

Jerry Nichols, MD is board certified in Physical Medicine and Rehabilitation with Carilion Clinic.
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