Therapeutic heating — “thermotherapy” for therapy geeks — is more useful than most people realize, mainly because muscle is a source of more and worse pain than most people realize, and muscle pain pain seems to respond well to heat. Muscle pain caused by over-exertion, muscle cramps and spams, and especially trigger points (muscle “knots”) are all common and sometimes severe, but often mistaken for other kinds of problems.
This therapeutic staple has mostly been ignored by science: it’s benefits are far from proven, and obviously it’s no miracle cure.1 Nevertheless, it’s probably doing more than “just” relieving symptoms. (Not that we should knock symptom relief.2) Everyone should understand heating the same way everyone knows how to put on a bandaid: it is a cheap, drugless way of taking the edge off an amazing array of common painful problems, especially neck and back pain, and maybe more.
Heat is primarily for relaxation, comfort, and reassurance, and taking the edge off of several kinds of body pain, mostly duller and persistent pains associated with stiffness, cramping, and/or sensitivity, which can be loosely categorized:
There are many other kinds of pain, of course, but these are the ones most likely to benefit from heat. No one with appendicitis or a 2nd degree burn wants a nice hot water bottle.
Heat will make some conditions much worse. Never apply heat to an infection or fresh injury! Or any other acutely inflammation, like a flare-up of arthritis. Just don’t do it! That’s what ice is for: soothing inflamed tissue.
And what’s a “fresh” injury? Any time tissue has been physically damaged, it will be inflamed for a few days, give or take. If superficial tissue is sensitive to touch, if the skin is hot and red, if there is swelling, these are all signs that your injury is still fresh, and should not be heated.5
If there’s no obvious/severe injury or infection, it’s okay to try a heat treatment. But it can be surprisingly unclear!
Sometimes it’s really tough to tell if pain is due to an injury. This is the puzzle at the centre of many chronic pain problems: the distinction between feeling damaged and being damaged. This is the puzzle at the centre of many chronic pain problems: the distinction between feeling damaged & being damaged. Several kinds of pain exist in a gray area between the two.
The best example is probably muscle strains versus muscle “knots.” A strain is an actual rip in the muscle — physical damage, while a “knot” or trigger point (TrP) is an irritable patch of tissue, probably a micro-spasm (more about this below). The difference between a minor strain and a bad trigger point can be subtle.6 And yet you want to heat the knot, not the strain! Fortunately, if the strain is mild enough that you can’t tell if it’s a strain, it’s probably not a big deal one way or another: just try some heat and see what happens.
But there are many situations where this kind of ambiguity is a challenge, like low back pain.7
If you suspect a muscle strain, but you’re not sure, here’s a good tutorial for helping you sort it out: Save Yourself from Muscle Strain! If back pain is your issue and you’re not sure what’s causing it, get thee to another tutorial: Save Yourself from Low Back Pain! And I have an article specifically devoted to helping people understand why heating back pain is usually better than icing it: (Almost) Never Use Ice on Low Back Pain!
The next several sections explore different mechanisms and details of how heating might be helpful to people in pain:
Our comfort zone is a warm place. And so, almost no matter what kind of pain you have…
To reduce pain, we need to reduce credible evidence of danger & increase credible evidence of safety.
Lorimer Moseley. Explainer: what is pain and what is happening when we feel it? TheConversation.com.
The brain probably interprets a safe source of warmth as good “credible evidence of safety,” for basic psychological reasons related to the environmental and social conditions we evolved in. Cold kills! Hypothermia has been at or near the top of the list of threats to our safety throughout all of prehistory and most of history.8 And we also associate warmth with contact and intimacy — another powerful goodness.
So a nice controlled source of warmth is probably just about the most basic reassuring thing there is. And that’s always good for pain.9 You might mistake this for a psychological effect, and it is in a sense, but it’s more useful to look at it as “applied neurology”: leveraging what we know about how pain neurology works. It’s more akin to triggering a reflex than a mind game.
Roughly a degree celcius or two at a couple centimetres depth, give or take, depending on how and where it’s done.
Scientists have tested this. For instance, in 1998, Draper et al heated subjects triceps muscles with hot packs for fifteen minutes, and then checked their temperature with a needle probe — like a very thin meat thermometer (don’t worry, they were anaesthetized).10 They found an average increase of 3.8˚C at a depth of one centimetre, and .78˚ at three centimetres.
I think this data clearly shows that superficial heating is an easy way to modestly increase tissue temperature up to a couple centimetres — which is most of the volume of most muscles — for whatever that’s worth. The 3.8˚C increase in the muscle shallows is something, but .78˚ change at 3cm depth — and a lot of muscle is that deep — is clinically trivial, well within the range of healthy variations in core body temperature.
A trigger point is a small patch of acutely sensitive soft tissue, a poorly understood little patch of sensory misery. They are probably contracted, stagnant, swampy11 sections of muscle tissue — but that’s just a theory.12
However they work, no one doubts that these sensitive spots in muscle are common. They can cause anything from stiffness and dull aching to show-stopping agony. The pain often spreads in confusing patterns, and they grow like weeds around other painful problems and injuries, making them interesting and tricky and incredibly common.
And heat seems to be a particularly good therapy for trigger points. Never formally tested! But plausible.
Trigger points are probably aggravated by stress, and (as noted above) being warm is a pleasant and comforting sensation, as long as we aren’t overheated to begin with. But it probably goes beyond that…
Relaxation reduces resting muscle tone. You can have “tight” muscles without actually being in frank spasm. There are many degrees of muscle tone between deep relaxation and a charlie horse. Many otherwise healthy people live in a state of uncomfortably high muscle tone, their muscles always a little clenched and exhausted, probably with some specific areas even worse from awkward working postures. This state is inherently uncomfortable, like being tired from exercise — but without the endorphins — and it may be fertile ground for trigger points. If so, any reduction in muscle tone may be quite helpful.
Perhaps the most popular therapeutic reason to get into a hot tub is to try to beat the pain of DOMS (delayed-onset muscle soreness) — that nasty 24–28 hours of muscle pain you get after unfamiliar exercise. But DOMS is mostly invincible. Researchers have proven over and over again that there really is no effective treatment for it.
Except, maybe, heat?
For a long time, “warm underwater jet massage” — hot tub jets — was the only treatment that had ever shown any potential, in a 1995 study.13 But it was a small and flawed piece of research — and most people know from personal experience that a soak in a hot tub may “take the edge off,” but hardly constitutes a miracle cure for DOMS. I mostly ignored that evidence.
In 2006, we got some good science news: more persuasive data, surprisingly good results in treating DOMS in the low back with a “heat wrap,” a wearable device that applies heat for hours at a time.14 Another small study, but this time more persuasive one. Eureka? Proof needs more data, but this makes it well worth trying heat on your sore muscles after exercise. Happy heating!
Ointments and balms like Tiger Balm15 or RUB A535 and Deep Heat are not really hot, but they do have two things in common with heat — they both feel hot, and they both cause superficial capillaries to open up as wide as they can.
Capsaicin is a classic rubefacient — it’s the stuff that makes chilli peppers spicy, on your tongue or your back.
All these products contain a chemical irritant or rubefacient (and there’s your word-of-the-day). Rubefacients feel hot because they give you a mild chemical burn! Capsaicin is a classic rubefacient — it’s the stuff that makes chilli peppers spicy, on your tongue or your back. They piss off your skin, in other words. That’s the only sense in which a rubefacient is heating anything. The product name “Deep Heat” always makes me roll my eyes, because a more truthful name would be Shallow Irritation! “Chemicals that are mild skin irritants may make a patient feel warm,” wrote Borrell et al, “but they will not produce any in vivo temperature rises or any of the physiological effects of heat.”16 The effect is just too superficial.
And is a mild chemical burn helpful in any way? The most basic modern rationale for a rubefacient is that it’s a counter-irritant — a neurological distraction from your pain. Counter-irritation is a real thing, but it’s not a powerful effect. You could call it another tool for the pain treatment toolbox, but it’s not an impressive tool, maybe just like a small screwdriver or a tack hammer.
Many rubefacients also have touted medicinal and pain-killing effects. For instance, garlic is supposed to be good for all kinds of things, salicylates are definitely medicinal in some applications, and capsaicin has gotten a lot of high fives and thumps on the back from science17, some of them quite interesting.18 But of course any such benefits are just bonus prizes that have nothing to do with heating.
There are many ways to heat yourself up, but two broad categories: local and systemic.
Local heating means specific heating: applying a hot water bottle, heating pad, heated gel pack or bean bag to a specific place on the body.
Systemic heating means raising the entire body temperature with a bath or jacuzzi, steam bath, or piping hot shower — basically creating an artificial fever!
For most local heating, I recommend seeking out a large-sized (14 × 27) Thermophore, the Rolls Royce of heating pads: large, heavy, thick, and moist. Yes, moist — they produce a moist heat with “a special tightly-woven fleece blend cover which retains moisture from the air.” If you leave a Thermophore on a plastic surface, there will be beads of water under it five minutes later. The moisture captured from the air by the Thermophore conducts heat far more effectively than a dry heating pad. Luxurious! Both genuine Thermophores (roughly USD $50-100) and cheaper knock-offs (and probably nearly as good) can be ordered online from Relaxus.com, and are also available in some medical supply stores. Of course, Amazon.com has them, too.
Full-body heating in hot tubs, showers, saunas and steam rooms is also often helpful factor with conditions where emotional stress and/or knots in your muscles are the cause of your troubles, or a significant complicating factor — low back pain is the most obvious example. See A Better Hot Bath for tips on getting the most out of your bathtub or Jacuzzi. Believe it or not, many people do not really know how to take a bath! There are several simple tips that can definitely wring more therapeutic value out of the experience. (Adding Epsom salts to a bath is not one of them, however — it’s popular, but probably useless.)
I am a science writer, former massage therapist, and I was the assistant editor at ScienceBasedMedicine.org 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.
— Added evidence of efficacy of NSAIDs for common injuries.
— A series of substantial upgrades, details unlogged.
Muscle tension can cause a surprising amount of pain. A leg or foot cramp is a common and extreme example, where no one has any doubt of the cause of pain. But imagine a muscle spasm much less strong, but lasting for days and days — or years! Although superficially a simple concept, there are actually several physiological mechanisms by which muscle can become shortened and painful for a long time, some well understood and straightforward (spasticity from neurological diseases), while others are quite mysterious (like spasms peole are born with, as in torticollis or wry neck).
One excellent example of neuropathic spasticity is the “MS hug”: a symptom of multiple sclerosis that feels like a painfully tight band around the chest, often experienced long before diagnosis. Although the feeling of constriction is the classic symptom, many patients also just experience widespread pain in the chest wall.BACK TO TEXT
This significant paper demonstrates that the biochemical milieu of trigger points is acidic and contains many pain-causing metabolites. For much more information about this, see Toxic Muscle Knots.BACK TO TEXT
“This drug is generally considered safe when used according to the directions on its labeling. But taking more than the recommended amount can cause liver damage, ranging from abnormalities in liver function blood tests, to acute liver failure, and even death.”BACK TO TEXT