How Do TENS Units Work? An Overview of TENS Therapy
Transcutaneous electrical nerve stimulation (TENS) uses a low-voltage electrical current to block the effects of pain signals. It's often used to relieve pain caused by arthritis, autoimmune disorders, and other chronic health conditions. But how do TENS units work? The following guide provides an overview of TENS therapy, explains the benefits, and answers some of the most frequently asked questions about TENS devices.
What is TENS Therapy?
TENS therapy is the use of a battery-powered device to deliver a low-voltage electrical current to the target area. The current is conducted through electrodes, which are small patches with a medical-grade adhesive that helps them stick to the skin. During a treatment session, the technician places electrodes on the sensitive areas of the body that have been causing pain and discomfort. If TENS therapy is being performed by an acupuncturist, the treatment provider may connect the device to acupuncture needles instead of using the skin patches.
Although physical therapists, acupuncturists, and other health professionals use TENS therapy in their practices, at-home TENS devices make it much easier to get relief from chronic pain. These devices are easy to use and eliminate the need for people with chronic pain to take time out of their busy schedules to drive to a treatment clinic every time they need TENS therapy pain relief.
An at-home TENS machine also makes this type of therapy much more affordable, as there's no need to pay a copay for each treatment session or worry about whether a treatment provider is in-network or out-of-network with a specific insurance plan.
What are the Benefits?
One of the main benefits of a TENS unit is that it can activate opioid receptors in the brain, relieving pain and reducing or eliminating the need for patients to take prescription pain medications. An article published in Pain Management indicates that high-frequency TENS therapy may even be more effective than opiates at relieving pain.
In people with fibromyalgia and other autoimmune disorders, TENS therapy may reduce the body's tendency to overreact to pain signals, a problem known as hyperalgesia. Reducing the body's sensitivity to pain signals lessens the pain for such patients, making them feel more comfortable overall. Additionally, TENS therapy can even reduce fatigue in patients with fibromyalgia, leading to increased productivity and improved quality of life.
How Do TENS Units Work?
So, how does a TENS unit work? A TENS machine has several components that work together to deliver electrical impulses to the treatment site. For example, Caputron's TENS 3000 device has a 9V battery, 45" lead wires, and four electrode pads. Once the machine is set up, the lead wires are attached to the electrode pads, enabling the delivery of electrical impulses to the painful part of the body.
The Gate Control Theory of Pain
Pain researchers believe that TENS therapy relieves pain in one of two ways. According to the gate control theory of pain, the spinal cord has a series of gates that allow pain signals to travel to the brain. Depending on the circumstances, these gates may be open more on some days than others, causing people to feel different levels of pain at different times. If the gates are more open than usual, more pain signals travel to the brain, causing higher levels of pain. When the gates are more closed than usual, a person's pain level is likely to be lower due to the reduced number of pain signals that make it to the brain.
These theoretical gates tend to be more open when someone is experiencing a high level of stress or boredom. The gates may also open up more than usual due to a lack of physical activity. Researchers who support the gate control theory of pain believe that TENS therapy relieves discomfort by disrupting the transmission of pain signals. Transcutaneous electrical nerve stimulation acts as a form of counter-stimulation, relieving pain by causing the control gates to be less open than they were before the treatment session.
The Endorphin Release Theory
Another potential explanation for why TENS therapy is so effective is the endorphin release theory, which states that endorphins have morphine-like effects that help reduce pain. Endorphins are chemicals released in response to pain or stress. Under this theory, TENS therapy is effective for pain management because the electrical impulses produced by the TENS unit stimulate the release of endorphins, preventing pain signals from reaching the brain. As a result, TENS therapy helps relieve pain caused by a variety of conditions.
Types of TENS Therapies
Although the principles of TENS are the same regardless of the device and treatment setting used, different TENS techniques are used to achieve specific treatment goals. Conventional TENS therapy, which uses low-intensity, high-frequency electrical impulses, is the most common. In this context, high-frequency means 50 to 100 Hz. The aim of conventional TENS therapy is to stimulate the neurons responsible for carrying pain signals to the brain.
Acupuncture-like TENS (AL-TENS) may be helpful for people who don't respond well to conventional TENS therapy. This type of TENS uses high-intensity, low-frequency (2 to 4 Hz) electrical impulses. While conventional TENS stimulates large-diameter neurons, AL-TENS stimulates neurons with smaller diameters.
Intense TENS also stimulates small-diameter neurons, but it uses high intensities and high frequencies to block pain signals in the peripheral nerves. Unlike conventional TENS, which causes little to no discomfort, intense TENS can only be used for short periods of time due to high-frequency electrical impulses. This type of TENS therapy is typically used in professional treatment settings, such as when a doctor removes sutures or a nurse changes a hospital patient's wound dressing.
TENS Therapy for Pain Relief
TENS therapy is used to relieve pain caused by acute and chronic medical conditions. Many of these conditions cause joint or muscle inflammation that can lead to long-term discomfort. Although TENS has many applications, it's most often used to relieve pain caused by the following:
- Arthritis: Arthritis is a medical condition that causes joint pain, stiffness, and swelling. According to the Arthritis Foundation, TENS helps relieve arthritis-related pain and reduces the need for people living with arthritis to take pain medications. An analysis of TENS research published in the Cochrane Database of Systematic Reviews supports this claim, as the authors found that TENS therapy produced a "significant benefit of pain relief" in patients with osteoarthritis of the knee. In addition, patients also reported reduced knee joint stiffness after receiving TENS therapy.
- Bursitis: Bursa are fluid-filled sacs that reduce friction between the joints. If one of these sacs becomes inflamed, a condition known as bursitis, the inflammation can cause pain and reduced mobility. TENS therapy helps relieve bursitis-related pain.
- Fibromyalgia: Fibromyalgia causes widespread pain, fatigue, and other symptoms. Researchers are still searching for the exact cause of the disorder, it's possible fibromyalgia develops in people who don't perceive pain normally. TENS therapy has been shown to reduce pain, fatigue, and sensitivity to pain signals in people with this disorder.
- Neuropathic pain: Neuropathy occurs when the peripheral nerves are damaged, resulting in pain, weakness, and other symptoms. The prescription medications used to treat this condition cause undesirable side effects in some people, prompting researchers to look for effective alternatives. According to an article published in Evidence-Based Medicine, TENS therapy is effective for reducing pain in people that have been diagnosed with neuropathy. When the authors of this article compared the use of TENS with sham TENS, TENS reduced pain one to two more points on a 10-point scale.
- Back pain: When it comes to pain relief, many people prefer a TENS unit for back pain. Although TENS is effective, it doesn't have as many side effects as prescription medications or surgical procedures. TENS therapy is also noninvasive and less expensive than many other treatment options. Researchers have even been conducting clinical trials to explore the use of TENS therapy in emergency departments and other hospital settings.
TENS therapy can also be used for muscle pain, chronic pelvic pain, tendinitis, and other conditions that cause pain and discomfort.
How to Use a TENS Machine
A TENS machine is simple to use and makes it much easier to relieve pain without prescription or over-the-counter medications. Before starting a TENS therapy session, make sure the treatment site is clean and dry. Inspect the skin to make sure there are no cuts, open wounds, or other types of skin damage. If you notice any skin damage, delay your first TENS session until the skin has healed completely.
Make sure the TENS unit is off when you're ready to begin. Follow the instructions to insert the battery or charge the unit so it has enough power to use it. Connect the lead wires to the skin patches (electrodes) that came with the TENS machine. Plug in the lead wires, apply the patches to your skin, and make sure the patches aren't touching each other. Before turning on the machine, ensure that the patches aren't in contact with any metal objects, including jewelry, belt buckles, or medical ID bracelets.
Turn on the machine and follow the directions that came with the TENS unit to deliver the electrical impulses to he treatment area. TENS units have more than one setting, so take the opportunity to adjust the intensity of the electrical impulses. They should be strong, but they shouldn't cause any pain or discomfort. During the treatment session, you may feel like the impulses are getting less intense over time. If this happens, adjust the intensity until you feel strong impulses again.
When the treatment session ends, turn off the unit and disconnect the lead wires from the electrodes. Be careful not to tug on the wires. If you plan to use the TENS unit again later in the day, leave the patches on your skin so you don't need to apply them a second time. If you're finished using the TENS, remove the patches and store them according to the instructions that came with the TENS device. Put the machine and the electrodes in a safe place until you're ready for your next TENS therapy session.
Tips on How to Use a TENS Unit
If you've never used a TENS unit, there's nothing to be worried about. TENS units are easy to operate and come with everything you need to successfully complete a treatment session. That said, it's always helpful to review some tips for using and maintaining the device. Follow these tips to make your TENS therapy as effective as possible:
- Take the time to clean your skin before each session. Applying the patches to clean skin extends the life of the adhesive, eliminating the need to replace the skin patches frequently.
- Keep the electrodes in the liner or storage bag that came with your TENS unit. Otherwise, the adhesive may get less sticky over time, forcing you to replace the electrodes earlier than anticipated.
- You don't have to sit still while using a TENS unit. If you have a belt clip, you can use the TENS on your lower body and keep your arms and hands-free for reading, using the computer, and performing other activities.
- Yanking the lead wires away from the skin patches can damage the electrodes, preventing them from delivering electrical impulses as intended. Spend a few extra seconds to disconnect them gently from the skin patches.
- Store your TENS machine in a cool, dry place to protect it against moisture and extreme temperatures. Never submerge the device in water or store it in an area that's prone to leaks from windows, air conditioning units, and other sources.
- If you don't feel pain relief right away, don't give up on TENS therapy. Experiment with different settings until you find one that works to relieve your pain. You may need to use the TENS device several times before you start to notice a difference.
Frequently Asked Questions About TENS Devices
Is it safe to use a TENS machine if I have a medical condition?
TENS therapy is non-invasive and safe for most people, but not everyone is a good candidate. For example, people with implantable medical devices should not try TENS therapy because the electrical impulses can interfere with the normal operation of those devices. Pacemakers, neurostimulators, and cardioverter-defibrillators are just a few of the devices that should not be used with a TENS machine.
Some medical conditions also preclude people with acute and chronic pain from using TENS therapy for pain relief. One of the biggest contraindications is damaged skin. The electrical impulses produced by a TENS device are safe for healthy skin, but if the skin is already damaged, then applying an electrical current may cause the wound to get worse. The presence of scar tissue may also prevent the use of TENS therapy, as the skin around the scar tissue may have reduced sensation, making it difficult for the person receiving the treatment to provide feedback about the intensity of the electrical impulses.
The following conditions may also prevent the use of TENS therapy. If you have one of these conditions, talk to your doctor before trying TENS at home or scheduling an appointment with a physical therapist or acupuncturist:
- Blood clots
- Heart disease
- Cognitive impairment
How long does TENS pain relief last?
TENS therapy typically provides pain relief for a few hours up to one full day. This is why TENS therapy is delivered in many sessions over time rather than in a single treatment session.
Does TENS therapy cause any side effects?
Many people experience no TENS machine side effects, but the electrical impulses may produce a buzzing or prickling sensation at the treatment site. It's also possible to have an allergic reaction to the adhesive in the electrodes. This type of reaction usually causes skin redness and irritation that goes away once the electrodes are removed, and the skin has a chance to heal.
Conclusion and Considerations
TENS therapy is safe and effective for most people. It's also noninvasive and can reduce or eliminate the need for some people to rely on prescription pain medications to work, go to school, and engage in leisure activities.