TENS UNITS

All You Need To Know

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by Matthew Henderson, MPT

Masters of Physical Therapy

Updated: Nov 16th, 2022

Jump to The Best TENS Units

A TENS unit is a small device that delivers electrical impulses through electrodes placed on your skin to help relieve pain.

THE BASICS

HOW TENS WORK

The primary theory behind pain relief with TENS units is called the "Gate Control Theory." The electrical current stimulates the nerves that carry signals relating to tactile senses (i.e. touch.) The signals travel to the spinal cord where they block the transmission of pain sensations to the brain. The electrical charge may also stimulate the release of natural hormones, such as endorphins, that decrease your pain levels. These are essentially hormones that exist in the brain and are released when the body experiences stress.

PROS AND CONS

Let's start with the pros of TENS units. First, they are convenient, portable, and new models are about the size of a cell phone. You can easily adjust the intensity to find the level providing the most relief. TENS are low-risk, non-invasive and have few significant side effects. Some individuals are able to reduce their reliance on pain medications with TENS. Regarding cons: The adhesive pads may cause skin irritation (hypoallergenic pads are now available for sensitive skin), they can be expensive, and you cannot use TENS on certain areas of the body. See the precautions below for a full list of areas to avoid.

THE EVIDENCE

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EVIDENCE RATING: FAIR+

TENS technology and it's clinical validation is complicated. Used in Physical Therapy and Pain clinics for decades, the technology has a strong following both with clinicians and clients. However, attempts to lock down the effectivenes off TENS have provide difficult due to the many factors involved. Namely, treatment duration, pad placements, high vs low frequency, type of injury treated, duration of pain to date etc. We have done our best to provide a concise and informative review of the literature below. INTENSITY The intensity of stimulation appears to be crucial. Low intensities have been shown to be largely ineffective at controlling pain (1-3.) Based on these studies it would appear inadequate intensities studied in one of the primary factors attributed to conflicting reports of TENS efficacy. This indicates users should aim for the maximally tolerated intensity to achieve the most pain relief. TOLERANCE Repeated and long-term use of TENS appears to produce a habituation effect (4,5.) Prevention of TENS tolerance appears to be inhibited by modulating between low and high-frequencies during treatment (6), or by increasing the intensity of the TENS daily (7.) LOW BACK PAIN Systematic reviews that have examined the efficacy of TENS for low back pain have offered conflicting results from effective (8), inconclusive (9), to not effective (10.) We will note the "not effective" study appears to have used a pre-designated setting of 15mA, which based on the data we reviewed was less than half the required intensity for the spine (30mA.) Thus, it is not clear if TENS is effective for low back pain. OSTEOARTHRITIS AND JOINT PAIN Once again, the results were mixed with some studies finding significant relief (11,12) and others showing no effect (13.) Once again, the intensities varied widely in these studies, and two trials did not even report TENS intensity (14,15.) Overall, the evidence supporting the use of TENS for pain relief with the correct intensity level is rated a FAIR+. It is important to use a higher intensity and adopt strategies/technologies to reduce the development of tolerance over time. Additional studies with more rigorous methods are also needed.

REFERENCED STUDIES

1. Aarskog R, Johnson MI, Demmink JH, et al. Is mechanical pain threshold after transcutaneous electrical nerve stimulation (TENS) increased locally and unilaterally? A randomized placebo-controlled trial in healthy subjects. Physiother. Res. Int. 2007;12:251–263. https://pubmed.ncbi.nlm.nih.gov/17957730/ 2.Pantaleao MA, Laurino MF, Gallego NL, et al. Adjusting pulse amplitude during TENS application produces greater hypoalgesia. J. Pain. 2011;12(5):581–590. https://pubmed.ncbi.nlm.nih.gov/21277840/ 3.Claydon LS, Chesterton LS. Does transcutaneous electrical nerve stimulation (TENS) produce ‘dose-responses’? A review of systematic reviews on chronic pain. Phys. Ther. Rev. 2008;13:450–463. https://www.tandfonline.com/doi/abs/10.1179/174328808X373998 4. Chandran P, Sluka KA. Development of opioid tolerance with repeated transcutaneous electrical nerve stimulation administration. Pain. 2003;102:195–201. https://pubmed.ncbi.nlm.nih.gov/12620611/ 5. Liebano R, Rakel B, Vance C, et al. An investigation of the development of analgesic tolerance to transcutaneous electrical nerve stimulation (TENS) in humans. Pain. 2011;152:335–342. https://pubmed.ncbi.nlm.nih.gov/21144659/ 6. DeSantana JM, Santana-Filho VJ, Sluka KA. Modulation between high- and low-frequency transcutaneous electric nerve stimulation delays the development of analgesic tolerance in arthritic rats. Arch. Phys. Med. Rehabil. 2008;89:754–780. https://pubmed.ncbi.nlm.nih.gov/18374009/ 7. Sato KL, Sanada LS, Rakel BA, Sluka KA. Increasing intensity of TENS prevents analgesic tolerance in rats. J. Pain. 2012;13:884–890. https://pubmed.ncbi.nlm.nih.gov/22858165/ 8. Machado LA, Kamper SJ, Herbert RD, Maher CG, McAuley JH. Analgesic effects of treatments for non-specific low back pain: a meta-analysis of placebo-controlled randomized trials. Rheumatology (Oxford) 2009;48:520–527. 9. Khadilkar A, Odebiyi DO, Brosseau L, Wells GA. Transcutaneous electrical nerve stimulation (TENS) versus placebo for chronic low-back pain. Cochrane Database Syst. Rev. 2008;4:CD003008. 10. Dubinsky RM, Miyasaki J. Assessment: efficacy of transcutaneous electric nerve stimulation in the treatment of pain in neurologic disorders (an evidence-based review): report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology. Neurology. 2010;74:173–176. 11. Osiri M, Welch V, Brosseau L, et al. Transcutaneous electrical nerve stimulation for knee osteoarthritis. Cochrane Database Syst. Rev. 2000;4:CD002823. 12. Bjordal JM, Johnson MI, Lopes-Martins RA, Bogen B, Chow R, Ljunggren AE. Short-term efficacy of physical interventions in osteoarthritic knee pain. A systematic review and meta-analysis of randomised placebo-controlled trials. BMC Musculoskelet. Disord. 2007;8:51. 13. Rutjes AW, Nuesch E, Sterchi R, et al. Transcutaneous electrostimulation for osteoarthritis of the knee. Cochrane Database Syst. Rev. 2009;4:CD002823. 14. Quirk AS, Newman RJ, Newman KJ. An evaluation of interferential therapy, shortwave diathermy, and exercise in the treatment of osteoarthritis of the knee. Physiotherapy. 1985;71:55–57. 15. Smith CR, Lewith GT, Machin D. TNS and osteo-arthritic pain. Preliminary study to establish a controlled method of assessing transcutaneous nerve stimulation as a treatment for the pain caused by osteoarthritis of the knee. Physiotherapy. 1983;69:266–268

HOW TO USE

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APPLYING TENS

To get the most out of your TENS device it is important to use it correctly. We'll break this into a few key points. WHAT INTENSITY LEVEL? When you first turn on the TENS unit, you will begin to feel a slight buzzing sensation as you slowly turn up the intensity. You may see your muscles start twitching, which is fine, but you do not want the intensity to ever become painful. Continue increasing the level until it feels significant but, once again, NOT painful. Based on the research we reviewed, you want to err on the side of a slightly higher intensity to get the most pain relief possible. WHERE TO PLACE THE PADS Feel around with your fingers until you have ascertained the central region of your pain. This may take some time. You will then place the pads around that spot. - The pads should not be touching - Try to keep them no more than 2-3 inches apart - Do not place them directly on bones or joints - Never use the units while operating heavy machinery, driving, or any other activity where an involuntary muscle twitch could lead to an injury or accident. - Minimize activity during your session (this is mostly to keep the pads from falling off.) MAINTAINING THE PADS Pads can get expensive. You want yours to last. After each session, wipe the pads with antiseptic alcohol tissues. This will remove any oil or hair and help keep them sticky. Also, make sure you put the pads back on the plastic strips. TAKE HOME While we may have made this sound complicated, it's really not. After just one or two sessions, you will be a pro and set up your TENS unit is just a few seconds.

PRECAUTIONS

Do not use TENS pads over or close to the areas where an electronic device is implanted (pacemakers, spinal stimulators etc.) If you have epilepsy, do not apply to your head, neck or shoulders. The impulses could potentially cause seizures. If you are pregnant, do not apply the TENS unit anywhere near the uterus. This includes the low back, abdomen, pelvic area etc. NOTE: TENS has been used for labor pain in the past, but only under direct supervision of a clinician. Do not apply to any region with known or suspected cancer. Do not apply TENS to the chest region if you have heart disease, arrythmias or other cardiac issues. Do not apply TENS is you have a bleeding disorder or recent bleeding issues. Do not use TENS if you have a suspected blood clot or DVT (Deep Vein Thrombosis) as this increases the risk of dislodging the blood clot. Once again, do not place the pads directly on bones or joints. Do not have the pads touching. Do not set the TENS at an intensity that is painful. Don't use while wet or in the water.

TENS units are a non-drug, pain relief tool that has been used widely in the clinic and general population for many years. Low risk. Research has Fair+ support for TENS solely for pain relief. Best used to control pain in order to better tolerate therapeutic exercises and remain active.

CONCLUSIONS

THE BEST

Dr. Ho's   |   PowerDots   |   iReliev

 

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Our favorite, the Dr. Ho's Pain Therapy 4 pads system is unapologetically old school, but with some exciting new technology. To be exact, we chose Dr. Ho's due to their proprietary Auto-Modulating Pulse technology. This feature allows over 300 different stimulation techniques to keep the body guessing and reduce the tendency of your body to habituate over time to the treatment. The AMP technology resonated to us due to our research review, which noted the best way to minimize tolerance to TENS was to alternate between high and lower frequencies. Dr. Ho's is leveraging these findings.

Regarding the company: We spoke with their CEO, Vincent Ho, and were impressed with their dedication to build a multi-disciplinary team of clinical advisors. As Mr. Ho put it, "We want every type of clinician having a voice in our product development and testing." With a group including physicians, physical therapists, and chiropractors - they appear to be committed to this approach. 

 

The AMP feature was even more compelling when combined with their reputation for reliability, excellent customer service, great value, and ease of use. 

 

​PROS

  • Great value

  • Auto-Modulating Pain technology

  • Reputation for excellent customer service

  • Easy to use

  • Adaptable for multiple regions

  • Auto-timer

 

​CONS

  • - Wires can be tricky at times

  • - No smartphone app

The next generation of TENS units are here. This device automatically connects with bluetooth and turn your smartphone into the controller. The app is intuitive and easy-to-use. Connect the pads and power-unit to the painful area, select the body part on the app, and you are ready to go. 

The simplicity of the set-up particularly resonated with us. The PowerDot's Smart TENS program also allows you to set pain scores and track progress. We think this is a critical piece that no other product is current offering. Quantifying the progress (or lack thereof), is key to determining if you are actually on the right path to recovery.

We are going to go ahead and call it the Tesla of TENS units, with it's over the air auto-updates, such as the clever Loan Haul Flight mode. If you have automatic updates on your phone, the newest features will always be available. That's pretty neat.

You also have over 100 levels of intensity. This is compared to most other models which are more in the 10-20 intensity levels range.

PROS

  • Discreet design

  • Excellent app

  • Personalized programming

  • Numerous step-by-step videos

  • Auto-updates

  • 100 intensity levels

CONS

  • You must use the PowerDot electrodes (no swapping out for cheaper versions)

  • Short wires limit size of area for treatment

  • Higher cost

No wires. Zip. Nada. We found this very useful and discreet. Very simple to use. Designed with just four buttons, it is very straightforward. Using two wireless pads with the iReliev is equivalent to using four pads on many other devices. This is because it requires only one pad per channel (positive and negative.) This makes it quick and simple to take on and off the pads, however, it does slightly limit the size of the area you can treat. 

Each pad can be set independently with program and intensity levels. This is nice if you are experiencing different areas of pain, but we don't think it will be super helpful for most users.

Setting up the device and pairing it with the wireless receiver pads is straightforward as well. We did note the screen is very small.

PROS

  • No wires!

  • Discreet pain relief

  • Simple and easy to use

  • One pad does the job of two

  • 25 intensity levels

  • Subscription service for pads

  • Priced reasonably

CONS

  • No app

  • Small screen

  • No Auto-Modulating feature