Sensible advice for aches, pains & injuries

Zapped! Does TENS work for pain?

The peculiar popularity of being gently zapped with electrical stimulation therapy

by Paul Ingraham, Vancouver, Canadabio
I am a science writer and a former Registered Massage Therapist with a decade of experience treating tough pain cases. I was the Assistant Editor of for several years. I’ve written hundreds of articles and several books, and I’m known for readable but heavily referenced analysis, with a touch of sass. I am a runner and ultimate player. • more about memore about
Photograph of a woman using the Thync product, a kind of electrical stimulator that “uses low-energy waveforms to safely and comfortably signal nerves on your head and face. These nerves signal specific areas of the brain that cause your body to relax or energize.”

The Thync

A fresh take on the TENS concept: an electrical stimulator worn over the right temple that either invigorates or relaxes with the right “vibes.”


Transcutaneous electrical nerve stimulation (TENS) tries to treat pain by passing alternating current through superficial tissues causing tingling sensations, with brief and minor benefits that are probably just a “sensation-enhanced” placebo. It has been a therapeutic staple in physical therapy and chronic pain clinics for decades, and there are many consumer TENS gadgets. They are safe and fairly cheap at about $100 for a typical unit.

It’s not as scientific as it seems, but it may not be useless either: interesting sensations can always get something done when presented in the right way to patients. The tingling and vibrating might “drown out” pain, “distract” the nervous system from it, or get the brain to “reconsider” pain. It’s remotely possible that TENS stimulates actual tissue behaviour change (healing) and not just sensation. In theory, the right setting could make all the difference, which makes the topic endlessly debatable, even though most TENS obviously doesn’t work many miracles.

TENS has always also been seen as a form of relaxation therapy, similar to a vibrating massager, but it’s probably a minor effect. It doesn’t seem to be able to prevent (for instance) jaw muscle clencing in TMJ syndrome.

There’s not much scientific evidence that TENS helps pain and it’s surprisingly well-studied as these things go (much better than ultrasound, oddly). As of 2016, there are five disappointingly non-positive reviews, two spankings of TENS for for back pain and osteoarthritis, and just one positive review (also the oldest). Despite this, some experts remain remain optimistic that the right TENS for the right kind of pain could still be good medicine.

There are many other electrotherapies. Electrical muscle stimulation (instead of nerve) might help keep muscles fit during rehab from injuries, but it’s probably no better than just clenching muscles yourself. Pulsed electromagnetic field therapy (PEMF) is a fascinating cousin of TENS that seems to actually directly stimulate cellular repair, and is an evidence-based method of speeding up fracture healing; it probably has other uses, but none have been confirmed yet. Central nervous system stimulation using surgically implanted electrodes is basically “deep TENS,” and is an area of active research. Old-timey galvanic baths were an old-timey whole body direct current stimulation, “spasm baths” with no clear purpose. People do seem like to like shocking themselves!

full article 5000 words

Humans love stimulants! We have always enjoyed zapping ourselves and each other, just a little bit, or even quite a lot.123 For many decades, by far the most popular (and tame) form of electrotherapy or neuromodulation4 has been transcutaneous electrical nerve stimulation (TENS). Other kinds of electrical stimulation are also interesting, and more promising, like deeper stimulation — zapping the brain and spinal cord. This is an overview of all forms of neuromodulation with a strong focus on TENS for pain, and don’t miss the good news at the end of the article about TENS’s complicated, awesome cousin: pulsed electromagnetic field therapy.

TENS has been a therapeutic staple in physical therapy and chronic pain clinics for decades. There are many consumer TENS units on the market. It has a huge following of believers, both providers and customers.

I do think we are heading into an era of using…both electrical & magnetic stimulation as a therapeutic tool.

Dr. Steven Novella, Nerve Stimulation for Relaxation

But people will believe anything! (You may have noticed this.) Much like ultrasound, this old-school techy therapy definitely isn’t all it’s cracked up to be: the effectiveness of TENS [NHS] “is based on individual experience rather than scientific evidence,” which seems odd for such a popular therapy. But it’s probably not entirely useless — interesting sensations, presented in the right way to patients, can always get something done (sensation-enhanced placebo).

Photograph of a man applying TENS electrodes to a woman’s upper back.

How does electrical stimulation work? And why would anyone want to do this?

If you stick a couple of electrodes on your skin and pump an electric current through your tissues, you will tickle your nerves and stimulate interesting sensations and/or some mild muscle contractions, which may temporarily drown out or disrupt pain. More about the biology below.

You can fiddle with various dials for different flavours of TENS. For instance, you can boost the intensity and frequency to get more muscle contraction.5 With a powerful enough unit (“These go to eleven.”), it is possible to “taze yourself.”

And so it’s possible that the right setting makes all the difference, just like with phasers. This makes the topic endlessly debatable, even though it’s obvious that TENS doesn’t work many miracles. In fact, it probably mostly doesn’t work much better for most pain than an aspirin, and it’s not much good for anything else except maybe some relaxation or gently exercising muscles in rehab.

And central stimulation?

And then there’s central stimulation — stimulation of the spinal cord or brain — the other major kind of neuromodulation. It’s kind of a big deal: more invasive, profound, and dangerous, and also used with more impressive results for more serious problems like Parkinson’s diseases, major depression, and serious chronic pain. It has roots in electroconvulsive therapy — “electroshock” therapy back in the day — but the modern era of electrical therapy began when deep brain stimulation was introduced in 1987, and it’s been steadily improving since then, mostly thanks to better surgical techniques for implants.

Now, if only we knew how it worked. No one actually does, and there are several possibilities, like vagus nerve stimulation to control inflammation for rheumatoid arthritis — extremely interesting, but far from an established effect.6 That’s an advanced topic, beyond the scope of this article for now.

TENS costs and safety

TENS units can be had for around $100, or even less for a few bargain models, but it is possible to spend several hundred on more power, options, or trendiness.

Picture of an electric shock warning sign.

TENS seems like it might be dangerous…but it’s not.

Although there is a tiny risk of mild shock from faulty devices, consumer TENS units are just too weak to be dangerous, and the risk of too much juice in a medical setting is extremely low.7 Overzealous self-treatment might cause some skin irritation around the electrodes.

Could TENS cause pain or other neurological symptoms?

Other than direct injury, it’s conceivable that TENS could backfire and actually cause pain instead of relieving it. I’ve wondered about this, and went looking for evidence of it — and found none. If it occurs, it’s rare and relatively minor.

But I still think it’s plausible. Any unusual stimulus can potentially be a trigger for the symptoms of certain diseases (migraine triggers like chocolate and wine are a classic example). A TENS backfire would not involve any harm to the nerves themselves, just a sensory over-reaction.8 Many cases of backfiring might not quite reach the level of pain. For instance, mild numbness, tingling, and other paresthesias are also possible. These are extremely common symptoms in people even when we aren’t pumping electric current through our flesh, and they usually are completely harmless and temporary, triggered by a variety of minor physiological and psychological circumstances. The strange sensations of TENS, for some patients, might trigger an “attack” of tingling or numbness.

The best defense against such reactions to TENS — or any weird stimulus — is mental confidence and optimism.

Is there any scientific evidence that TENS works for pain?

There’s some evidence that TENS helps pain, but it’s a bit sketchy. Superficial TENS is well-studied as these things go: there have been enough studies that there are several reviews of the studies. However, a lot of the reviews were inconclusive, because they’re reviewing a lot of weak data. Par for the course in musculoskeletal medicine, unfortunately: garbage in, garbage out.

An overview of TENS reviews
Milne 20019 negative review of 5 trials of TENS for chronic low back pain
Johnson 200710 positive review of 38 trials of TENS for chronic musculoskeletal pain, “effective”
Nnoaham 200811 inconclusive review of 25 studies of TENS for chronic pain
Khadilkar 200812 inconclusive review of 4 trials of TENS for chronic low back pain
Walsh 200913 inconclusive review of 12 trials of TENS for acute pain
Hurlow 201214 inconclusive review of 3 trials of TENS for cancer pain
Vance 201415 mixed review: “it’s complicated” but promising
Chen 201516 negative review of 18 trials of TENS for knee osteoarthritis
Desmeules 201617 inconclusive (but discouraging) review of 6 trials of TENS for rotator cuff tendinopathy

That doesn’t look great: five disappointingly non-positive,18 two spankings for back pain and osteoarthritis, and just the one clearly positive review out of seven (which is also one of the oldest and perhaps the least picky).19

But that 2014 one… “it’s complicated” is an understatement! Vance et al is a more formal and thorough version of what I’m doing here.20 Although it’s dense reading, they do a good job of putting it all in perspective, and point out several reasons why the evidence reviewed here is probably not the whole story, and why they remain optimistic that the right TENS (intensity, duration) for the right kind of pain could still be good medicine.

That kind of talk is often a red flag,21 But sometimes it’s fair, and this might be one of those times. Maybe science hasn’t asked the right questions yet. Despite the messy evidence, Vance et al. believe that “both high-frequency and low-frequency TENS have been shown to provide analgesia specifically when applied at a strong, non-painful intensity.”

My official position for now is that it probably works well enough for some patients to be worth trying if you’re desperate…but keep your expectations low. There are solid reasons to doubt that TENS can work well.

Photograph of an unusual TENS unit, with a pair of thick electrodes, about an inch square, that seem to have batteries built into them, attached to the arm of a woman.

This novel TENS unit has batteries built into the electrodes. (Photo by Philips Communications, license, image unmodified.)

If TENS works, how does it work? Digging deeper into the biology

The reason it might work is probably the same reason it can only work so well.

Pain is completely controlled by an overprotective brain that likes to sound the alarm too loudly, too often, regardless of what’s actually going on in tissues. This makes most kinds of pain partially and briefly treatable with tricks and hacks.22 Unfortunately, your brain is stubborn and it’s hard to convince it to shut up about pain completely — short of knocking it out, which is why anaesthesia is the only truly effective analgesia.

The brain decides what hurts based on many sources of information. TENS messes with that system. It blasts the nervous system with static, sensory white noise. By stimulating nerves in this strange way, TENS doses the brain with unusual sensory information, which either “drowns out” information about tissue damage, and/or simply distracts the brain and forces re-evaluation. If it happened without warning or explanation, it would probably be scary and make the pain worse. But pay good money for it and call it “therapy,” and it can be reassuring instead. Context is everything!

But TENS cannot actually stop the brain from doing its job! Unless you turned it up enough to actually disable your brain.23 If your brain thinks you need to be in pain, the alarm is going to start going off again sooner or later — maybe right after the TENS is turned off.

Basically what all of this means is that TENS is what I call sensation-enhanced placebo. Placebo is “relief from belief,” and the belief can be (greatly) enhanced by novel sensations. Every placebo involves some degree of fundamentally dishonest exaggeration to make the patient believe that it’s better than it actually is. Treatments that produce unusual sensations have an advantage, because the unusual sensation makes the treatment seem much more legitimate and special. If you take this far enough, it seems less like a placebo and more like we’re doing something therapeutic to the body. But if it boils down to convincing the patient’s brain to dial down the pain, it’s still a placebo at heart — just a clever, fancy one.

TENS for muscle knots

The most common kind of musculoskeletal pain that doesn’t have an obvious cause is probably the “muscle knot” or “trigger point” — a patch of sensitive soft tissue, which is still mysterious after decades of sparring with it scientifically. All we really know for sure is that they feel like aching muscle, and they’ve inspired a lot of theories and half-baked cures.24 Trigger points are as likely a target for TENS as anything else, and it’s safe and cheap enough to be worth trying in difficult cases.

A 1997 study of TENS specifically for treating these little monsters found positive results.25 Yes, you read that right: positive! Some good news for once. Of course, the “just one small study” disclaimer applies in a big way: one study never proves anything, and I think this is the only one of its kind. But it was a reasonably good experiment, and the results were promising.

They compared nerve stimulation, muscle stimulation, and a placebo for 60 patients with knots in their shoulders (trapezius). They measured pain, pressure sensitivity, and range of motion (neck sidebend) before and after treatment. Muscle stimulation improved range of motion (but not pain/sensitivity), and nerve stimulation improved pain/sensitivity (but not range).26 The authors concluded:

ENS is more effective for immediate relief of myofascial trigger point pain than EMS, and EMS has a better effect on immediate release of muscle tightness than ENS.

The effects were statistically significant, but not clinically dramatic enough for them to boast about. But there’s enough here that I really wish someone would try the experiment again with more people. Maybe someday!

Electrical muscle stimulation: EMS vs. ENS

Athlete squatting with four-channel, electrical muscle stimulation machine for training, attached through self-adhesive pads to her quadriceps.

Athlete adding power to her squats — literally! — with an EMS machine. By Gciriani, CC BY-SA 4.0

Just as electrical stimulation can be shallow or deep, there’s also electrical nerve stimulation (ENS) or electrical muscle stimulation (EMS).27 The right electrode placement and settings will stimulate muscles more than nerves, forcing them to contract. And so EMS may be a useful trick for exercising muscles, useful either in rehabilitation or, perhaps, performance enhancement. EMS feels like doing light isometric muscle contraction exercises — that is, clenching muscles without moving joints.

Whereas ENS is primarily used to try to treat pain, EMS is mostly meant for athletic training and performance enhancement — which is speculative and somewhat optimistic but not necessarily totally out to lunch — and rehabilitative scenarios like preventing muscles from atrophying from disuse after trauma, which makes sense and seems to work.28

Many readers are curious to know specifically if EMS can help them maintain fitness when otherwise resting or incapacitated from an injury, especially stubborn overuse injuries like runner’s knee or plantar fasciitis that may require a period of substantial resting before a tedious phase of “baby steps” rehabilitative exercise. That’s exactly what EMS is good for, in theory, but in practice the benefits are probably trivial, and nothing you couldn’t get just as well or more so with isometrics, and more conveniently to boot. Half-arsed optimization of muscle conditioning in the early stages of rehab should not be a high priority for most people. The exceptions would be people who are more profoundly injured, or have specialized training needs due to a progressive disease.

And then there’s the entertainment value. EMS is kinda neat. If you just like the idea of messing around with it for the kicks and novelty, knock yourself out — figuratively speaking.

More TENS claims: relaxation

Photograph of a scalp vibrator head massage tool.

A scalp vibrator—similar to TENS in principle.

Are you tense? Try some TENS! It’s probably at least a little bit relaxing, and anything truly relaxing is at least a little bit good for pain — but only a little bit. Relaxation is weak medicine, as anyone with chronic pain can tell you. TENS has always been seen as a trivially relaxing therapy, just like a vibrating massager is: it literally vibrates muscle, as well as producing buzzing and tingling sensations that are quite similar to the feeling of vibration.

These days, the relaxation claims are fancier. (Almost everything about TENS device is fancier these days.29)

What if TENS could stimulate specific nerves in a specific way, to create a more profound effect? That’s what the Thync (pictured at the top of the article) is supposedly doing, and either relaxing or invigorating depending on what mode it’s in: “Thync uses neurosignaling to activate30 specific cranial and peripheral nerves… signalling brain regions to change the way you feel.” Unsurprisingly, skeptical neurologist Dr. Steven Novella’s late 2015 review of the Thync is discouraging.31 For me, $200 is not an outrageous price for a little interesting experimenting on myself, and I’ll probably try it for fun. But I’m keeping my expectations low. If I’m really serious about getting into a deeply relaxed state, I suspect practicing meditation would offer better bang for buck. Or even just a hot bath.

And how about the more traditional approach? For instance, how about using TENS to reduce jaw clenching in a patient with temporomandibular joint syndrome? It’s a good example to consider, because it’s a classic example of the combination of muscle clenching and pain. If TENS is relaxing, it should be able to help this problem. The evidence is very limited and mixed. A little 2001 study is the only reasonably well-designed test I could find. It compared TENS to biofeedback in 20 patients. Unfortunately, neither method had any effect: those jaw muscles kept right on clenching, as measured by EMG.32 That is a bummer.

And I’d still try it if I had temporomandibular joint syndrome. The right settings could make the difference!

MOAR! Whole body TENS, anyone? Old timey galvanic baths

As if there aren’t enough TENS options with a few electrodes and several dials, you can — if you’re eccentric — run current through your whole body in an electric bath. This current would hopefully only be direct (galvanic) current for safety.33 But for the same reason it’s safer, direct current is also less stimulating: it causes a smooth, sustained muscle contraction, whereas the alternating current of TENS makes your muscles vibrate. Sounds relaxing, eh? Spasm baths!

Vintage photo of a man in galvanic bath, seated on a chair between a pair of basins for his legs and a pair for his arms. There’s some old timey electrical hardware on the wall above him.

Do not try at home.

Galvanic baths are mostly an old-timey thing you would have a hard time trying even if you wanted to, but they are an entertaining example of electric therapy.

“What is so strange about a galvanic bath?” one reader asked me. I suppose it’s not quite as outrageous as it looks, but it does reek of what could possibly go wrong? And, medically speaking, it’s quite a bit farther out in left field than TENS, quite unlikely to be good for anything. There’s no known or plausible therapeutic mechanism other than “it feels kinda funny.”

If nothing else, galvanic bathing was doomed to extinction by economics: the high cost of the infrastructure and equipment to deliver such treatments is way out of proportion to the slim hope of any significant benefit. Plus, can you imagine the lawsuits it would generate today?

TENS has a complicated, awesome cousin: pulsed electromagnetic field therapy

Pulsed electromagnetic field therapy (PEMF) is clearly kin to TENS, part of the electrotherapy family. And yet it’s a different beast, much more exotic, with a more mysterious mechanism of action. PEMF is hypothesized to directly stimulate cellular repair, and not for nothing: it seems to really do that, and the effect is almost magical, speeding up bone fracture healing, and even restoring it in cases where healing has failed completely.34

The scientific reviews of PEMF used for this purpose are astonishingly, unstintingly positive.3536 When does this happen in musculoskeletal medicine? Never, that’s when!

So PEMF has been used on fractures for a long time now, but only recently have PEMF devices gotten small and cheap enough for consumers and less critical medical applications. Can they work on more ordinary problems? Like arthritis? Something TENS can only treat effectively with just the right settings and variables, that no one can seem to confirm?

Apparently so. Although the evidence for this isn’t unanimous, some of the best and most recent PEMF trials are unambiguously positive.37 Even though there’s some hope for TENS with just the right settings, the best evidence is only lukewarm, and confirmation awaits better trials of just the right sort of TENS for the right sort of patients. Meanwhile, PEMF is just looking rather good, and I think it’s probably worth a try.

Photograph of knee wearing ActiPatch Knee Pain Relief product.

PEMF devices are widely available to consumers & not very expensive: ActiPatch® was the product tested by Bagnato et al. Although “clinically proven” is still a bit of a reach, ActiPatch seems to be closer to it than most products that make the claim. (No, they are not paying me for this endorsement. I wish!)

About Paul Ingraham

Headshot of Paul Ingraham, short hair, neat beard, suit jacket.

I am a science writer, former massage therapist, and I was the assistant editor at for several years. I have had my share of injuries and pain challenges as a runner and ultimate player. My wife and I live in downtown Vancouver, Canada. See my full bio and qualifications, or my blog, Writerly. You might run into me on Facebook or Twitter.

Related Reading

The Road to Wellville is a 1994 comedy/drama that depicted fashionable old-timey zapping at an unusual early 20th century health care facility, run by the eccentric Dr. Kellogg. Although it’s not a fantastic film, it’s not bad, and probably worthwhile for many health care professionals.

What’s new in this article?

Five updates have been logged for this article since publication (2016). All updates are logged to show a long term commitment to quality, accuracy, and currency. more Like good footnotes, update logging sets apart from most other health websites and blogs. It’s fine print, but important fine print, in the same spirit of transparency as the editing history available for Wikipedia pages.

I log any change to articles that might be of interest to a keen reader. Complete update logging started in 2016. Prior to that, I only logged major updates for the most popular and controversial articles.

See the What’s New? page for updates to all recent site updates.

2016Added a note about the potential of vagus nerve stimulation to control inflammation.

2016Added a mobile-only article summary. Added a paragraph about sensation-enhanced placebo.

2016Minor science update, added a new review (Desmeules) of TENS for rotator cuff tendinopathy.

2016Added more information about possible harms, a really bad pun, a link to The Road to Wellville, and a reader comment about the “fancyness” of TENS devices over the years.

2016Added section about pulsed electromagnetic field therapy.



  1. Most famously, in 1963, the Milgram experiment supposedly showed that people are surprisingly willing to inflict extremely painful and even dangerous shocks on other people. To this day, it is cited as an demonstration of the human capacity for evil done by “just following orders,” but this is a misinterpretation that has become a myth. Happily, there are many sound criticisms of the classic interpretation, and lots of follow-up science has shown that people are actually quite reluctant to zap each other. BACK TO TEXT
  2. Running current through our bodies is just the tip of the iceberg when it comes to potentially self-destructive treatments. You’ll think I’m bullshitting you, but voluntary lobotomy was actually faddish once. What could possibly go wrong?! See Popular but Weird & Dangerous Cures. BACK TO TEXT
  3. There have been many abuses of electrotherapies, but the winner for paving the road to hell with good intentions must surely be the chapter in the history of autism treatment when cattle prods were promoted to parents as “tingle sticks” to modify the behaviour of their autistic children. Seriously. See Neurotribes: The Legacy of Autism and the Future of Neurodiversity. BACK TO TEXT
  4. Neuromodulation is the umbrella concept for all kinds of nerve stimulation, mostly with electricity. It’s defined by the International Neuromodulation Society as “the alteration of nerve activity through the delivery of electrical stimulation or chemical agents to targeted sites of the body.” The point of neuromodulation of any kind is to normalize nerve function, to get nerves to behave differently, and hopefully better. Many different kinds of electromagnetic stimuli are used for this. BACK TO TEXT
  5. Push that far enough and things get much more “interesting.” Fortunately, consumer units don’t go to 11 on that scale — to simulate rigor mortis, you’d need a proper generator. BACK TO TEXT
  6. Koopman FA, Chavan SS, Miljko S, et al. Vagus nerve stimulation inhibits cytokine production and attenuates disease severity in rheumatoid arthritis. Proc Natl Acad Sci U S A. 2016 Jul;113(29):8284–9. PubMed #27382171. PainSci #53670.

    Vagus nerve stimulation sure sounds great (maybe a little too great): stimulate your vagus nerve with an implant, et voila, less systemic inflammation. There’s broad biological plausibility here, but almost no evidence — this idea hinges only on the results of this one study so far. Koopman et al. tested it on humans and reported that “these results establish that vagus nerve stimulation targeting the inflammatory reflex modulates TNF production and reduces inflammation in humans.”

    Established, eh? Not without replication! That’s overconfident for sure — this needs replication before celebration.

    All kinds of data hijinks could be hiding in a study this technical. My main concern is the use of the word “significantly” in the abstract, without any details (effect size in particular). All too often that wording, without clarification, means there was a statistically significant but clinically trivial result. With many treatment trials I can go digging for the effect size to confirm, but not here, the reading is too difficult for me to form any meaningful impression without spending an hour, and even then it might not be clear. And even if the paper does indicate a clinically meaningful result it’s still got “too good to be true” written all over it and may well prove to be difficult to reproduce.

    But it’s a genuinely interesting topic, I think.

  7. As of 2016, there seem to be hardly any complaints on the Internet about trouble with these devices — which is remarkable, considering that we’re talking about very large numbers of humans playing with devices that are intended to deliver electric current. BACK TO TEXT
  8. It would be a case of the brain interpreting the unusual stimulation as threat rather than therapy. Mental context is everything, and so I would expect it to occur mainly in vulnerable and sensitive tissues, and people with higher anxiety and lower pain tolerance for any reason. BACK TO TEXT
  9. Milne S, Welch V, Brosseau L, et al. Transcutaneous electrical nerve stimulation (TENS) for chronic low back pain. Cochrane Database Syst Rev. 2001;(2):CD003008. PubMed #11406059. BACK TO TEXT
  10. Johnson M, Martinson M. Efficacy of electrical nerve stimulation for chronic musculoskeletal pain: a meta-analysis of randomized controlled trials. Pain. 2007;130(1-2):157–165. PubMed #17383095. BACK TO TEXT
  11. Nnoaham KE, Kumbang J. Transcutaneous electrical nerve stimulation (TENS) for chronic pain. Cochrane Database Syst Rev. 2008;(3):CD003222. PubMed #18646088. BACK TO TEXT
  12. 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. PubMed #18843638. BACK TO TEXT
  13. Walsh DM, Howe TE, Johnson MI, Sluka KA. Transcutaneous electrical nerve stimulation for acute pain. Cochrane Database Syst Rev. 2009;(2):CD006142. PubMed #19370629. BACK TO TEXT
  14. Hurlow A, Bennett MI, Robb KA, et al. Transcutaneous electric nerve stimulation (TENS) for cancer pain in adults. Cochrane Database Syst Rev. 2012;3:CD006276. PubMed #22419313. BACK TO TEXT
  15. Vance CG, Dailey DL, Rakel BA, Sluka KA. Using TENS for pain control: the state of the evidence. Pain Manag. 2014 May;4(3):197–209. PubMed #24953072. PainSci #54034. BACK TO TEXT
  16. Chen LX, Zhou ZR, Li YL, et al. Transcutaneous Electrical Nerve Stimulation in Patients with Knee Osteoarthritis: Evidence from Randomized Controlled Trials. Clin J Pain. 2015 Mar. PubMed #25803757. BACK TO TEXT
  17. Desmeules F, Boudreault J, Roy JS, et al. Efficacy of transcutaneous electrical nerve stimulation for rotator cuff tendinopathy: a systematic review. Physiotherapy. 2016 Mar;102(1):41–9. PubMed #26619821. BACK TO TEXT
  18. “Inconclusive” is definitely closer to a negative conclusion than a positive one: if TENS worked well, even small and poor quality studies would probably show it, all the more so because many of them were probably done by researchers who were hoping to get a positive result. A high risk of bias combined with scanty data usually produces tentatively positive conclusions! BACK TO TEXT
  19. The number of studies included generally reflects how picky the authors were about excluding poor quality studies, and it might be important that the one positive review included the largest number of studies — obviously including plenty of data that other review authors considered to be poor quality. BACK TO TEXT
  20. That is, it’s not a meta-analysis, a statistical summary of the results of many studies, but “review” in the more familiar sense: exploring and critiquing the data we have so far, and speculating about its significance. BACK TO TEXT
  21. You see it all the time in defence of snake oils and quackery. It’s called “special pleading”: the scientific equivalent of a bratty kid coming up with reasons why the rules shouldn’t apply to them. BACK TO TEXT
  22. Most treatments for pain work by fool their brain into thinking there’s no cause for alarm, at least for a little while. Almost any reassuring and/or distracting sensation has some potential to persuade the brain to dial pain down a bit. BACK TO TEXT
  23. And that was exactly the literal point of olde timey electroshock therapy originally: to completely overwhelm the brain and “short circuit” whatever undesirable thing it was up to, which was usually mental illness. A brain-disabling treatment. Interestingly, pain was rarely the rationale for electroshock therapy, because no one yet understood that the brain was the source of all pain — just like all other sensations and perceptions — and not the body as everyone assumed. BACK TO TEXT
  24. They are probably like tiny cramps — contracted, stagnant, swampy sections of muscle tissue — but that’s just a hypothesis, denounced by some experts. However they work, no one doubts that these sensitive spots in muscle are common. The pain often spreads in confusing patterns, and they grow like weeds around other painful problems, which makes them clinically interesting and tricky. Since we don’t really understand why trigger points occur in the first place, reliable and effective treatment is impossible. The best anyone can do is to experiment with therapeutic approaches, starting with the safest and cheapest things that make some sense. TENS is not at the top of that list of options, but it’s probably somewhere in the top third of it. BACK TO TEXT
  25. Hsueh TC, Cheng PT, Kuan TS, Hong CZ. The immediate effectiveness of electrical nerve stimulation and electrical muscle stimulation on myofascial trigger points. Am J Phys Med Rehabil. 1997;76(6):471–476. BACK TO TEXT
  26. That’s an interesting difference — it suggests that the effect of a trigger point on muscle extensibility exists independently of how sensitive it is, which is a little surprising. Those properties “should” come and go together, according to the main hypothesis of how trigger points work: the point hurts and resists elongation because it’s contracted. It’s not clear why ENS/EMS would each relieve one without affecting the other. But such puzzles are typical of trigger point biology. No one really knows what the heck is actually going on. BACK TO TEXT
  27. They’re both “transcutaneous,” so you could also keep the T and call them TENS and TEMS, but this seems to be unusual in practice, and TEMS in particular is just not a term that actually gets used — Wikipedia doesn’t even list it as a possibility, whereas TENS is standard. Odd. BACK TO TEXT
  28. Hasegawa S, Kobayashi M, Arai R, et al. Effect of early implementation of electrical muscle stimulation to prevent muscle atrophy and weakness in patients after anterior cruciate ligament reconstruction. J Electromyogr Kinesiol. 2011 Aug;21(4):622–30. PubMed #21334221.

    This was test of electrical muscle stimulation (EMS) for rehabilitation after knee surgery. Twenty patients had acute anterior cruciate ligament tears repaired. Half of them got EMS after surgery, and half did not. “Muscle thickness of vastus lateralis and calf increased significantly 4 weeks after surgery in the EMS group, while it decreased significantly in the control group group. The decline of knee extension strength was significantly less in the EMS group than in the CON group at 4 weeks after the surgery, and the EMS group showed greater recovery of knee extension strength at 3 months after surgery.” The anti-atrophy effect of EMS was not dramatic, but it was clear.

  29. This reader comment from a long-time TENS user was interesting: “I’ve used TENS for 17 years on and off. One thing I have noticed over the years is that they sure have got a lot fancier in settings but the basic premise is still the same. But the new features don’t seem to make one jot of difference mentally or physically. The intensity can be increased or decreased, and that’s all.” BACK TO TEXT
  30. A mostly meaningless oversimplification, since the nerves aren’t “dormant” in any sense, and making them to produce signals is not in itself meaningful to the brain. Nerve stimulation cannot have any specific or inevitable effect on brain state, because it’s completely up to the brain to interpret the significance of nerve impulses — that’s the brain’s job, and there’s no known way to control that precisely with an unnatural external stimulus. BACK TO TEXT
  31. “The Thync device, in my opinion, is jumping the gun and making claims that go beyond the evidence. All they currently have is one small in-house study looking at one of their two claims (relaxation). Also, using one device stimulating at the same location for both relaxation and stimulation stretches plausibility.” BACK TO TEXT
  32. Wieselmann-Penkner K, Janda M, Lorenzoni M, Polansky R. A comparison of the muscular relaxation effect of TENS and EMG-biofeedback in patients with bruxism. J Oral Rehabil. 2001 Sep;28(9):849–53. PubMed #11580823. BACK TO TEXT
  33. Both kinds of current can be lethal if it’s enough current for long enough, but AC is much less comfortable at the same magnitude, and it’s better at making hearts freak out (fibrillation). It takes quite a bit more DC current to cause a heart attack. For instance, the “let-go current” is the highest current at which you can let go of a conductor: above the limit, you can’t let go! The limit for AC is just 22 mA, but 88 mA in DC. BACK TO TEXT
  34. This is known as “fracture nonunion,” a rare but extremely serious complication. “Normally a broken bone will begin to grow together in a few weeks if the ends are held close together to each other without movement. Occasionally, however, a bone will refuse to knit despite a year or more of casts and surgery. This is a disaster for the patient and a bitter defeat for the doctor, who must amputate the arm or leg and fit a prosthetic substitute.” Becker BACK TO TEXT
  35. Shi Hf, Xiong J, Chen Yx, et al. Early application of pulsed electromagnetic field in the treatment of postoperative delayed union of long-bone fractures: a prospective randomized controlled study. BMC Musculoskelet Disord. 2013;14:35. PubMed #23331333. PainSci #53405. “Fracture patients treated with an early application of PEMF achieved a significantly increased rate of union and an overall reduced suffering time compared with patients that receive PEMF after the 6 months or more of delayed union, as described by others.” BACK TO TEXT
  36. Assiotis A, Sachinis NP, Chalidis BE. Pulsed electromagnetic fields for the treatment of tibial delayed unions and nonunions. A prospective clinical study and review of the literature. J Orthop Surg Res. 2012;7:24. PubMed #22681718. PainSci #53378. “PEMF stimulation is an effective non-invasive method for addressing non-infected tibial union abnormalities. Its success is not associated with specific fracture or patient related variables and it couldn't be clearly considered a time-dependent phenomenon.” BACK TO TEXT
  37. Bagnato GL, Miceli G, Marino N, Sciortino D, Bagnato GF. Pulsed electromagnetic fields in knee osteoarthritis: a double blind, placebo-controlled, randomized clinical trial. Rheumatology (Oxford). 2016 Apr;55(4):755–62. PubMed #26705327. PainSci #53404.

    This was a scientifically rigorous test of wearable pulsed electromagnetic fields (PEMF) for older patients with osteoarthritis of the knee: moderate to severe cases with X-ray evidence and pain of at least 4/10 for more than six months, despite maximum tolerated medication. Sixty patients wore either a real PEMF device for 12 hours per day, or a fake; neither they nor the researchers knew who got real PEMF (double-blind). PEMF is particularly easy to test properly, because it causes no sensation, making it much easier to compare to an active placebo.

    The placebo devices do not emit a radiofrequency electromagnetic field but are identical to the active devices, including a light-emitting diode light showing operation. The energy from the active device is not felt by the user, and the active device cannot be distinguished in any way from the placebo device.

    Their pain and knee function were compared. PEMF won decisively: the real-PEMF patients enjoyed a 25.5% reduction in pain, compared to a 3.6% reduction for the fake-PEMF patients. Knee function improved as well, though not as much. I hope everyone got a real PEMF device at the end!

    That’s compelling evidence. Not that there aren’t caveats. (There are always caveats.) Although the results seem straightforwardly positive, the authors explain that “some of the effects of this therapeutic approach might be derived from neuromodulation of the pain mechanism”: that is, it might be “just” a pain-killer, as opposed to actually helping to heal arthritic cartilage. But killing pain effectively would be a pretty good second place!

    The Bioelectronics Corporation manufactures PEMF devices, and provided the pulsed electromagnetic fields and placebo devices, but they did not fund the study and the authors declared no conflict of interest. These devices are widely available to consumers: see ActiPatch®.