Detailed guides to painful problems, treatments & more

Cramps, Spasms, Tremors & Twitches

The biology and treatment of unwanted muscle contractions

Paul Ingraham • 50m read

Sometimes muscles contract when they shouldn’t. This can be merely weird and annoying, or painful, or even crippling. Although common and often unnerving, odd muscle contractions are rarely medically worrisome. There are many types of unwanted contractions, but many do not have a clear cause and are hard to even classify. The terminology is a bewildering mess, with many poorly understood and overlapping concepts.

The word “spasm” is notoriously vague, for instance, and yet is routinely used to “explain” musculoskeletal pain, whether it actually has anything to do with muscle contractions or not. “Cramp” also gets a lot of sloppy use beyond its main meaning (acute exertional cramps). These words are used almost reflexively to explain any kind of pain with no other obvious cause. And if spasm or cramp seems a little too dramatic, muscle “tightness” is an even more imprecise default scapegoat: a partial spasm? It’s all rather squishy.

But unwanted contractions are clearly real, and some are painful indeed. We know this all too well from the more dramatic common examples: menstrual cramps, a calf cramp during a soccer match, or being woken by a foot cramp. And so it’s reasonable to extrapolate from that and hypothesize: maybe less dramatic muscle contractions cause more aches and pains than anyone has investigated scientifically.

Animated illustration of a generic muscle contracting repeatedly.

Many kinds of spasms

Spasm” is an informal, non-specific term for any unwanted muscle contraction. It is often used to “explain” musculoskeletal pain — “my back is in spasm!” — when in fact the pain may have nothing to do with muscle contraction at all. Almost everything on this list is some kind of spasm. I will use “spasm” as a shorthand for “unwanted contraction” throughout this article.

The term “cramp” is almost as non-specific as spasm, but the term suggests a more intense, transient, and painful experience, and it is applied to some of the most familiar kinds of spasm. We’ll begin with those…

Important reassuring public service announcement: twitching and tremors rarely indicate a serious problem

Nearly all twitches and tremors are harmless and will never be explained. Like fatigue or abdominal pain, they are classic “non-specific” symptoms with endless possible causes. Un-like most other non-specific symptoms, they seem specific, and so they often freak people out. But they rarely indicate any serious pathology, and are commonly caused by:

  1. obvious factors like stress, anxiety, fatigue, excessive caffeine and “other” stimulants
  2. increases in neuromuscular irritability, which occur with many relatively minor pathologies, possibly so minor that there aren’t even any other symptoms, and you’ll just have to chalk it up to the weirdness of biology!

This is not to say that tremors and twitches are never a symptom of something more serious, of course. But in the absence of other worrisome signs and symptoms, the odds are overwhelmingly in your favour.

Pet Theory: Our motor control systems are fantastically complicated and delicate, and smooth operation of our muscles is the result of a miraculous physiological balancing act that gets a little off kilter surprisingly often. And yet there are also so many checks and balances that it’s hard to throw that system off a lot. This may be why spasms are so common, and yet mostly trivial.

Muscle contraction basics

The molecular machines that power muscle tissue are bundles of Velcro-like threads of proteins — but very feisty Velcro! Imagine if a strip of Velcro didn’t just stick, but all the hooks flexed in one direction, let go, grabbed again, flexed again, and so on, one half crawling on the other like an inchworm. That’s how the proteins do it, but at the dazzling speeds of the world of molecules. Multiply their microscopic crawling action by a zillion, and you get a macroscopic muscle contraction. For more about this amazing mechanism, see Micro Muscles and the Dance of the Sarcomeres.

The biochemistry of contraction is so complex that there’s still much that we don’t know about it9 … and plenty that can go wrong, some of it probably extremely subtle.

What’s even normal? Muscle behaviour is bizarre

To understand dysfunctional or pathological muscle behaviour, it’s important to understand normal muscle behaviour, so it’s too bad that we don’t. In addition to the deep microscopic mysteries about the biochemistry, there are serious outstanding scientific questions about things like:

Even something as seemingly simple as “normal muscle tone” is an elusive concept.

What’s a “spasm,” as in “my back is spasming”?

All known kinds of pathological contractions fit into one of the categories listed at the top of the article, like exertional cramps, spasticity, or dystonia. And yet a “back spasm” probably isn’t any of those things. It’s probably just a way of describing what back pain feels like … not what it actually is.

Unexplained musculoskeletal pain — especially back pain — is carelessly attributed to “spasms” by practically everyone. It’s a vague non-diagnosis with strong emotional appeal, which has been cynically exploited by pharmaceutical companies to sell muscle relaxants, which don’t work (covered below). It’s appealing because it’s simple and a lot of body pain just feels like a spasm, possibly because strong contractions may occur in the presence of pain with other causes.

Three major assumptions about “spasm” are often blended:

  1. spasms hurt — they are a major mechanism of pain, especially in the back and neck
  2. spasm is often “protective” — muscle guarding or splinting
  3. painful spasms cause themselves — a pain-spasm-pain vicious cycle

All of these are repeated ad nauseam by both clinicians and amateurs.12 Among the academics and experts, there’s a long, erratic history of debate over almost zero data, fighting over scraps. No one actually knows if they are true, and there’s a good chance they are not.

For many years I denounced them as myths, or misleading half truths at best. My contrarianism was overconfident, and based mainly on my deep distrust of vague claims. They smell like myths … but I can’t actually refute them with good evidence, because there is no such evidence. At best I can point to some red flags. Here are some basic concerns:

  1. Cramps are obviously painful, but so is the visible contraction of the muscle and its effect on joints. If back and neck pain are caused by contracting muscle, why can’t we see or at least feel it contracting? And why aren’t we actively fighting to keep the muscle elongated, as we must with cramps?
  2. If pain and spasm cause each other, why wouldn’t the vicious cycle escalate at least to the point of being an obviously contractile phenomenon like a cramp? It seems like it must either be so limited that it’s not very “vicious,” or it simply doesn’t happen. (And there is direct evidence against it.13)
  3. “Protective” muscle spasm clearly does not make biological sense with many injuries. For instance, it would be dangerous to strongly contract the muscles around a fracture: it would tear it apart!

Although those warning signs exist, there are also clinical clues that there are kernels of truth to these ideas about “spasm,” and it’s generally unwise to underestimate the complexity of muscle physiology and motor neurology. As with so much else in medicine, the truth is simply unknown. I explore the uncertainties as best I can throughout the rest of the article.

So what would cause sharp back pains, if not “spasm”?

Descriptions of back pain like “back spasms” and “throwing your back out” are just poetic, informal ways of labelling a sudden, intense onset of back pain … which can have many causes. And figuring out the cause of back pain is one of the trickiest problems in all of medicine, which is why I’ve written so much about it over the years (including a whole book, see The Complete Guide to Low Back Pain).

Sudden-onset back pain is a distinct type of back pain, and yet it still has many possible causes. People tend to think that the sharpness of the pain suggests injury or some specific mechanism — like spasm — but pain sharpness is less informative than you might think. Back pain often seems spasm-y probably because of our strong, muscular reaction to the pain: clenching and bracing! But these are reactions to the back pain, not the cause. The sensation of acute stiffness — which is complex, but basically boils down to uncomfortable movement — can also seem like muscle spasm.

The tricky idea of painful spasms

Can muscle contraction hurt? Is a lot of pain caused by contracting muscle? Cramps are certainly painful and thoroughly unsubtle. You can usually see cramping muscles bulging and flexing. They literally bend people out of shape and have to be fought with urgent stretching. Bad ones can be too strong to fight, and the worst can literally rip your muscles off the bone. The pain of a cramp is a warning of imminent trauma.

If there is such a thing as a painful spasm that is not a cramp, it must be an odd beast: strong enough to hurt a lot, but otherwise undetectable. How can a contraction be strong enough to hurt without the obvious bulging, flexing, and bending of a cramp? It’s not clear.

One simple explanation is that “spasm” is often just a way of saying “it hurts” while casually implying an incorrect explanation for why it hurts. And there are some obvious reasons why we might suspect contraction — stiffness and impaired movement around pain and injury. Three evidence-based points:

  1. Digging into the archives, a 1989 editorial decries the “preposterous” spasm diagnosis, describing “overwhelming evidence that skeletal muscle spasm is nonexistent.”14 Unfortunately, the author only mentions one 1950 study (which I can’t find), and a replication of it that he was involved in (which I also cannot find). But giving him some benefit of the doubt, he describes a study of 50 people with neck and/or shoulder discomfort, none of whom “had EMG evidence of muscle activity in the area of pain or in the proximal paraspinal muscle.”
  2. During my massage therapy career, I massaged hundreds of people who believed they had “spasms” that I couldn’t detect with my experienced hands, hands that could easily detect many other subtle things. In a more formal test, two doctors trained in manual medicine could not even identify the side of the body that neck pain was on by feel.1516 A neck muscle spasm so subtle that it defies detection even with direct, hands-on inspection cannot possibly involve much contraction.

    And one more thing about massage: if they’re caused by spasms, shouldn’t massage help a lot more than it does? I’m just asking!17

  3. Anticonvulsant drugs (like Lyrica) appear to be at least partially effective for spasticity/dystonia, but definitely do not work for back pain,18 suggesting that back pain is not normally caused by gross spasticity/dystonia.

But the truth is probably in the middle here. High muscle tone and a hardened, ropy texture are common in humans.19 In some cases, muscle tone may get high enough to be uncomfortable and “spasm” might be a reasonable way of describing it, albeit a little dramatic.

It’s a short hop from higher muscle tone to the more extreme and instructive example of spasticity — the name given to chronic contractions caused by some diseases. Not all of these are obvious, as with the “multiple sclerosis hug”: suffocating pain caused by complex dystonia of the muscles of the chest. The contractions aren’t obvious, but they cause great suffering. It’s clear from this example that rogue muscle behaviour can be painful without the nature of the problem being clear. “Spasms” seems like a fair way to describe that situation.

And could there be analogous discomfort in the neck or back? Maybe. Unfortunately, and rather incredibly, no one knows.

Protective muscle spasm (aka “muscle splinting”)

It’s also not clear that there is any such thing as a “protective” muscle spasm or “muscle splinting.” Muscle has a large behavioural repertoire, reacting in many ways to many different situations. There are undoubtedly competing and confused reflexes: situations where the body isn’t quite sure how to respond, and handles it differently over time and as conditions change. But a strong contraction around fragile tissue is a bad idea! You do not want muscles attached to a badly broken bone to spasm. Powerful contractions would injure healthy tissue!

What’s more likely? I can think of at least three plausible muscle behaviours that are “protective” without being “spasms” per se, or even the opposite:

  1. Shutdown! A tool the nervous system almost definitely uses to keep you safe is “inhibition,” protecting the injured area more by shutting it down than by tightening it up.20 The brain and spinal cord can decree that you simply aren’t going to move a joint until further notice, period, end of discussion, not a negotiation but a strict and powerful command: “DO NOT #%$!@!$ MOVE THAT.” You aren’t going to blast through a movement ban like that with will power. And such a lockdown — a perfect inability to move a body part — might well feel like “spasm,” when in fact it’s literally the opposite.

    “But it feels like spasm.” Yes, it does: but remember that stiffness is another imprecise word, and it describes a subjective sensation, a cousin of pain, not a specific physical state. Your brain’s reluctance to activate muscles manifests as a limited range of motion and the sensation of stiffness. It’s what “I can’t go there!” feels like.

  2. Flinching away! Another possibility is that protective spasm might function like a protective reflex: a strong, sudden contraction that stops you from proceeding in a potentially dangerous direction. Basically flinching away from something dangeous, except that the danger is inside you. Such contractions would be closely linked to pain: you try to move a certain way, and it hurts and your brain decides to yank you back from where you were headed with a sudden contraction … to prevent it from hurting even more! This is only a protective “spasm” insofar as it’s a sudden and not-up-to-you contraction, but it’s not a sustained “splinting” contraction either. And yet it does still seem reasonable to call it a “protective spasm.”

  3. Holding! Maybe there is a type of contraction that causes rigidity-without-shortening. “Isometric” contractions are contractions without movement, but this involves balanced contractions — quads and hamstrings contracting simultaneously to prevent movement — or matching an external force, and such a contraction would still be very hazardous around a broken bone. But perhaps there’s another way to contract without movement. I don’t know if this is actually possible, but there are reasons to suspect it, and muscle is definitely complex enough for such peculiar behaviour.

Tight and stiff — do they mean anything?

Our muscles can never be truly relaxed, short of paralysis. Living muscle is always on the job. There is a baseline level of mild contraction applying continuous tension to all our tendons, holding us together even when we are completely at rest. Contraction is not on/off, but a matter of degree, and the same muscle tone may be more or less functional in different ways for different people in different conditions.

And so the idea of “normal muscle tone” cannot be defined, or even be objectively measured. There is no tensionometer. What about subjective measurement, like when your massage therapist says you’re “tight”? Surely if anyone can detect muscle tension it’s a massage therapist! But no, not really: there’s a wide range of apparently healthy muscle texture; it seems to be only loosely related to any common aches and pains and stiffness, and devilishly difficult to assess. See You’re Really Tight.

Can you feel your own tightness? Probably — you can sure as hell feel a cramp! And many other pathologies that involve spasms.

And yet “stiffness” usually doesn’t describe a tissue state — it’s just a subjective feeling, a symptom, which correlates poorly with anything measurable (like a reduced range of motion). It’s likely that stiffness is more like a form of mild pain, and is a terrible way to judge muscle tone. See Why Do Muscles Feel Stiff and Tight?

The anaesthesia paralysis myth

It is a myth that muscles go completely limp during anaesthesia. They are not paralyzed. “There is a constant battle to relax the muscles during some procedures,” explains Dr. Steven Levin. The supposedly “paralyzed” muscle shrinks about 20% when cut. The tone is mediated by the brain and spinal cord. Some believe there is some intrinsic regulation of tone — that is, the muscle sets its own tone — but Dr. Levin directly refutes this with some pretty sound logic:21

Curare works at the neuro-muscular synapse, so it is the CNS that maintains the muscle tone, including the resting muscle tone (RMT). In my many years of doing surgery, I have never cut a muscle that did not retract unless it was curare-ized (and even then there is some contraction), so the tone has to be a primitive function, maybe some of it spinal, present even in deeply anesthetized creatures.

The take-home message here is that muscles are almost always contracting to some degree.

Exercise-induced cramps (and yet another myth)

Exercise unquestionably can induce cramping, but it’s unclear how or what to do about it. The main popular belief about what causes them is almost certainly wrong: it’s not the dehydration.

Infamously for those who have followed performance science in the 20th Century, cramps are not clearly caused by electrolyte loss from dehydration.2223 Chronic subtle dehydration is a popular scapegoat for cramping (and much else), but that’s probably even more wrong.24

If electrolyte loss caused cramps, we would fully expect supplementation to help — and people sure do. Oddly, this wildly popular belief remains ignored by science. The well-respected publisher of pooled data reviews, The Cochrane Collaboration, simply had no data to pool on this topic.25 You’d think someone would have studied magnesium for exercise-induced cramping by now (consider the value of the information in elite athletics) given its importance in elite athletics. But no! The data on magnesium for cramps due to pregnancy and disease is almost as scarce and mixed. For common unexplained cramping in adults (e.g. foot cramps in the night), there was just enough data to conclude that magnesium is “unlikely” to help.

What actually does cause exertional cramps (and therefore what prevents them) is still unknown (shocker). Here’s what little is known:

And that’s about it. There’s so much we still don’t know. Perhaps strangest of all is we don’t actually have a good explanation for why cramps hurt (even minor ones hurt, even when there’s nowhere near enough force involved to damage the muscle). Even muscle fatigue itself is something of a biological mystery.28

Hotshot in the dark: a spicy new cramp treatment?

Do we really have a cool new cure for athletic cramps? Have they been “un-invented”? And wouldn’t that be great?! Or … is it just another case of putting the marketing cart before the science horse? A good article from Dr. David Colquhoun about Hotshot anti-cramp product breaks it down for us:

[Hotshot provides] three references, two are to unpublished work. The third is not about Hotshot, but about pickle juice. … [the pickle juice results] are sufficiently suggestive that it might be worth testing Hotshot properly. One might have expected that would have been done before marketing started. It wasn’t.

And it still hasn’t been done (as of early 2018). Shocker.

The other critical point Dr. Colquhoun makes is that “it’s well known that nobody understands cramp.” Indeed, we just do not have a good grip on the biology of that malfunction, which makes it tough to treat. While it is possible to stumble on a cure for a mysterious problem — such things have happened before in the history of medicine (e.g. lithium jumps to mind) — most shot-in-the-dark treatments never pan out. So, wake me up when there’s good trial evidence.

Meanwhile, being prone to cramps myself, I look forward to trying some for kicks. Not that my personal experience with it will matter one whit. As Dr. Colquhoun points out, “There can be no condition more susceptible than muscle cramps to self-deception because of regression to the mean.”29

Myokymia: fatigue-induced muscle rippling and quivering, a fascinating muscle phenomenon

Muscle fibres do not normally contract all at once, as most people imagine. Instead they are organized into groups called “motor units,” one per motor nerve. Rather than firing all at once, the groups alternate their contractions, like pistons. At any given time, countless motor units are in different phases of contraction and relaxation. The units are so small and the switching system is so fast that their coordinated action seems to be completely smooth to us.

There is an interesting exception, though: if you get tired enough that a lot of motor units start failing to contract, the switching system fails because there aren’t enough motor units available for smooth contraction. This is why muscles start to ripple and quiver with intense exertions.

It’s a difficult thing to describe! Like thin bands of muscle twitching rapidly in waves under the skin. I’ve seen a few times, and you can’t really miss it: it’s an obvious, weird thing. Usually not dramatic, but distinctive. Hat tip to reader Chris for finding this video:

Rippling muscle disease  0:15

That’s very similar to what I’ve seen in my own quadriceps for years now,30 but with bigger, slower waves — my ripple is at least triple that speed. The difference could just be natural variation in the phenomenon, or something else altogether, but this looks more like my own experience than anything else I’ve seen on video.

It’s called “myokymia” … sort of

There’s not quite an official name for this. The obscure term myokymia is the closest thing to the right word. Wikipedia:

an involuntary, spontaneous, localised quivering of a few muscles, or bundles within a muscle, but which are insufficient to move a joint.

That’s just right … but in practice “myokymia” is mainly used to describe a symptom of muscle disease, not a benign and temporary effect of muscle exhaustion. Another common use is as a label for harmless-but-annoying quivering of the eyelids.

Sometimes this is called fasciculation, including by yours truly for many years until I learned better. Fasciculation is just the smartypants word for a twitch or spasm, as spelled out above.

The king of controversial contractions: the trigger point

People are chock-a-block with sensitive patches of soft tissue now popularly referred to as “trigger points.” No one denies the existence of these sensitive spots, but their nature has been controversial for a century. Conventional wisdom says they are tiny pathological contractions, which is why I’m including them in this article, but they could be a more pure neurological problem.

But I doubt it. I’m not saying they definitely are contractions … but they’re probably contractions.

I am uncomfortably aware that I sound like a crank to some experts when I talk about trigger points.

It’s not proven, but I believe the evidence is good enough for a moderate degree of confidence that the clinical phenomenon known as “trigger points” is indeed related to an objectively verifiable lesion in muscle tissue, and that lesion has characteristics that are consistent with a small contracture. High confidence is not justifed by the evidence available so far … but it’s good enough to justify cautious treatment, mostly massage and self-massage. Massage can be a pleasant and rewarding experience regardless of clinical effectiveness, and self-massage is safe and cheap. In other words, it’s well worth a shot.

The hiccup hack: suckin’ and swallowin’

This is about a hiccup cure that actually works because it sucks. (That will be funnier once I’ve had a chance to explain.)

Hiccups are not generally painful, but they are cousin to painful things.31 There are many quaint home remedies and folk cures for hiccups. But probably none of those work anywhere near as well as a FISST: a forced inspiratory suction and swallow tool.

The “Hiccaway” straw. It doesn’t suck. Not easily, anyway.

The HiccAway is a resistance straw, which means that it is a sucky straw for sucking. It doesn’t work at all well as a normal straw because it’s much too hard to pull water through it — by design. That’s the “forced inspiratory suction” part of the tool.

The “and swallow” part is because we can get some water through it. And we swallow that as it trickles through.

So using the straw combines a strong sucking action with swallowing, which is unusual. (Not exactly unheard of, but … okay, I think I’ve said enough.32)

The sucking + swallowing combo “short circuits” the hiccups. And this is actually an evidence-based cure, a weird but cromulent little neurological hack. The HiccAway:

stopped hiccups in nearly 92% cases and was rated favorably compared with home remedies across all demographic characteristics, hiccup frequencies, and hiccup durations.

That was the result of one kinda lame little clinical trial.33 Normally I would dismiss a study like that, but there are good reasons not to.34

And… it worked for me. This is a bit embarrassing, because I am so professionally allergic to using anecdotes. But … the results of the FISST study are completely consistent with my own personal experience with the device. It works

For whatever it is worth, I have tried the HiccAway this year (2022), and it has worked immediately and perfectly each of the half dozen or so times I’ve used it.35

What most interests me about this is that FISST’ing actually stops one kind of spasm. That gives me a little hope that there might be similar mechanisms for other kinds of spasms and cramps, especially the disabling and painful ones. That’s probably a bit of a reach,36 and I don’t know of any other similar example, unfortunately. But maybe it demonstrates that spasms aren’t entirely invincible … and that’s just nice to know.

Muscle relaxants

It sounds like such a great idea. Unfortunately, muscle relaxants are surprisingly impotent. The only kind of muscle relaxant that is over-the-counter is methocarbamol (Robaxin, etc), which mostly cannot outperform a placebo in tests.3738 Even a prescription muscle relaxant like carisoprodol is so ineffective that patients will (this is bizarre) actually tense up if they are lied to and told that the drug is a stimulant.39 Clearly the brain is the boss of your muscle tone.

Muscle relaxants are covered in more detail in several of my books: low back pain, neck pain, trigger points, frozen shoulder, headaches.

And what can boss your brain around? Sedatives …


The only true muscle relaxants are the sedatives, like diazepam, AKA Valium, a benzodiazepene (the best-known of several other notorious benzos like Klonopin, Ativan, and Xanax). These are the “nuclear option” — they interfere with muscle contraction, but they also interfere with a great deal else. (The barbiturates are another class of potent sedative, barely used anymore because they are so dangerous.)

Benzos involve serious risks of physical dependence and addiction, and withdrawal can be nightmarish and dangerous. Although it is possible for many people to get off benzos, many people do not get the information and help they need for that. Sadly, I have extensive personal experience with benzo withdrawal, and I’ve written about that in detail.40

Therapeutic Botox

The brand name “Botox” is a contraction of “botulinum toxin,” a potent neurotoxin that paralyzes muscle.41 Therefore, in theory, Botox has the potential to be helpful for any medical condition that is powered by spasm — not just wrinkles. Botox can even shut down some glands, which is why it is also used to treat things like excessive sweating or salivating (strange but true).

Unfortunately, it’s not often a great idea in practice, and wise prescription and delivery requires clinical expertise. There are several reasons why Botox might not be an easy win:

Despite all these caveats, there are cases where it probably does make sense to try. For instance, Botox is used to treat spasticity,46 especially if it’s severe, or caused by a serious disease (such that side effects and safety issues are the lesser of evils, sometimes by far). More examples of therapeutic Botox where its potential probably justifies the risks:

Therapeutic Botox is technical and complicated, and the debate continues on whether and how it should be used, especially for relatively minor musculoskeletal pain. Eye twitches are a great example of a condition in the Botox grey zone: it can make a lot of sense for severe and chronic cases with known pathological cause, but it would be reckless to inject Botox if the twitching is more likely caused by, say, exhaustion or a thyroid storm.

Many Botox providers advertise treatment for issues like neck and back pain, headache, jaw clenching, frozen shoulder, and trigger points — and all of these are much fuzzier targets. One reader commented that “every pain specialist I spoke to recommended Botox because they said they didn’t get results with steroid or anaesthetic injections.” I think Botox is probably used a little too freely and simplistically as a replacement for steroids or anaesthetic!

About Paul Ingraham

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

I am a science writer in Vancouver, Canada. I was a Registered Massage Therapist for a decade and the assistant editor of for several years. I’ve had many injuries as a runner and ultimate player, and I’ve been a chronic pain patient myself since 2015. Full bio. See you on Facebook or Twitter., or subscribe:

What’s new in this article?

Eighteen 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 When’s the last time you read a blog post and found a list of many changes made to that page since publication? Like good footnotes, this sets apart from other health websites and blogs. Although footnotes are more useful, the update logs are important. They are “fine print,” but more meaningful than most of the comments that most Internet pages waste pixels on.

I log any change to articles that might be of interest to a keen reader. Complete update logging of all noteworthy improvements to all articles 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.

Nov 10, 2023 — Added hemifacial spasm to the list of examples of pathological contractions.

2023 — Cited a case study about mistaking Parkinsonian dystonia for a knee injury.

2023 — Upgrades to the relatively new Botox section, including a few more citations, especially about harms and safety.

2022 — Substantial upgrades to the section “The hiccup hack” section.

2022 — Revised and expanded the introduction and summary; added menstrual cramps to the master list of familiar spasms; added a new small section, “The hiccup hack: forced inspiratory suction and swallow.”

2022 — New section about using Botox to treat unwanted contractions.

2021 — Added more information and science about exertional cramping and the role of magnesium in cramping.

2021 — Added mentions of restless leg syndrome and myoclonus, clarified the description of clonus, and expanded on my own experience with fasciculations.

2021 — Added a personal anecdote about successful treatment of a chronically twitching eyelid.

2020 — Added an unimportant but really interesting citation about non-local muscle fatigue.

2019 — Added the interesting example of vaginismus and pelvic floor spasm to the list of spasm types.

2019 — Added a little more detail about cramps.

2018 — Major revisions and more to do on the topic of “spasm,” protective spasm, and pain-spasm-pain vicious cycling. Also, new sections about muscle relaxants and sedatives.

2017 — Added discussion of tetany. Expanded on personal experience with fasciculations. Several clarifications and minor corrections.

2017 — Added a note about chronic dehydration; some speculation about why unwanted contraction is common but usually harmless; clarification of the spasm myth, and more about what does cause sharp back pains. Miscellaneous other changes.

2017 — New section: “Reassurances: twitching and tremors almost never indicate a serious problem.” Also added some more detail about my own strange example of myokymia.

2017 — Miscellaneous editing and minor improvements. Added new section “The myth of painful spasms.”

2017 — Major upgrade. Tripled the length of the article, an upgrade from a sketchy stub to a proper featured article, and now an official and worthy part of the library. Still plenty of sub-topics to come though!

2016 — Publication.


  1. That is, are the contractions inherently painful? Or is it just that the entire uterus and abdomen are inflamed and sensitive, and any physical disturbance would then be painful? The contractions might be painless without the inflammation! But that’s also a distinction without a difference, since they always occur together.

    On the other hand, the contractions might be powerful enough to be inherently painful, just like an exertional cramp.

  2. Ferreira D, Araújo R. A professional sportsperson with subtle motor symptoms and signs: early-onset Parkinson's disease. Lancet. 2023 Feb;401(10377):e18. PubMed 36841616 ❐ PainSci Bibliography 51317 ❐
  3. In 2014, I had an unforgettable battle royale with a twitch in my back (latissimus dorsi) that persisted, intermittent but frequent, for… eight months. These were strong contractions that would thump away at me, like someone knocking on my back, for 10–30 minutes at a time, several times per week, often disrupting sleep. To say that was frustrating and worrisome would be an understatement. In the early stages, I thought it was possible it would cause some kind of mental breakdown, but ultimately it simply demonstrated that the brain can adapt to almost anything. Eventually that particular twitch simply went away, and I have never felt it again since.

    I have a lot of experience with muscle twitching, more generally known as fasciculation, which is one of the reasons I wrote this article. It’s a part of my own struggles with chronic pain over the last several years. A random muscle goes off on me a couple times a day — delicate vibrations, erratic fluttering, or mighty cramp-like pulses. Most episodes last seconds or a few minutes at most, but a few times a year I get one that lasts for hours or days. The only consistent feature is a repeating contraction I didn’t order.

  4. There’s clearly a genetic component, but as of 2023 no one knows exactly how it works. There might be “fraying” of the nerve (damage over time from compression). Or “crossed wires” with another nerve (ephaptic transmission). Those mechanisms overlap with the theory of neuropathic “kindling,” where repeated or sustained stress increases vulnerability, a vicious cycle that turns a little fire into a big one.
  5. This phenomenon is tolerated as part of a therapeutic breathing exercise known as “bioenergetic breathing.” See: The Art of Bioenergetic Breathing: A potent tool for personal growth and transformation by breathing quickly and deeply.
  6. The disease “tetanus,” AKA lockjaw, is an infection with the bacterium Clostridium tetani, which causes powerful cramps.
  7. Women suffering from vaginismus often report a dramatic difference between the physical and functional size of their vagina. Intercourse can be physically impossible due to the contraction of the muscles of the vaginal wall and pelvic floor — a symptom that can worsen or improve, making it obvious that the physical limit is often significantly greater than what the muscles will allow.
  8. Gunter J. The Vagina Bible. 1st ed. Penguin Random House; 2019. Chapter 34: Pelvic Floor Spasm and Vaginismus; p. 297–304.
  9. We now know how molecular machines work in broad strokes — how “dumb” molecules can act alive, and produce orderly motion in the chaos of the “molecular storm” — and this is one of the great accomplishments of the last century of science. But many details are still missing, and the proteins that power muscle tissue are especially tricky. Difficult but highly recommended reading on this topic: Life's Ratchet.
  10. Halperin I, Chapman DW, Behm DG. Non-local muscle fatigue: effects and possible mechanisms. Eur J Appl Physiol. 2015 Oct;115(10):2031–48. PubMed 26330274 ❐

    Wear out your glutes or pecs … feel it in your cloits n dloits? Some experiments have been able to demonstrate this weirdness, others have not, and so it’s ontologically ambiguous (see Behm). If it exists, it seems to involve multiple pathways: “neurological, biochemical, biomechanical, and psychological.”

    And, if it exists, it obviously has Interesting Implications. If muscles you didn’t even exercise can feel exhausted, it’s equally plausible that they can also suffer other consequences. Like pain.

  11. Specifically, we still don’t know if it’s a neurological phenomenon, or if the tissue physically changes, or both.
  12. Some examples:

    • on spasm as a cause of back pain: “Muscle spasms in your back can be so painful that they may have you headed for the emergency room.”
    • on “protective” spasm: “A sustained involuntary muscle contraction that occurs after injury to the muscle as a protective mechanism to prevent further movement. Such spasms commonly result in muscle stiffness.”
    • on pain-spasm-pain: “By applying heat and compression simultaneously to muscles that are locked in the pain-spasm-pain cycle, massage engages four separate pathways that reduce pain, decrease spasm and increase circulation.”

    Claims like this are legion. They are literally never supported.

  13. Birznieks I, Burton AR, Macefield VG. The effects of experimental muscle and skin pain on the static stretch sensitivity of human muscle spindles in relaxed leg muscles. J Physiol. 2008 Jun;586(11):2713–23. PubMed 18403422 ❐ PainSci Bibliography 53112 ❐ “We conclude that, contrary to the ‘vicious cycle’ hypothesis, acute activation of muscle or skin nociceptors does not cause a reflex increase in fusimotor drive in humans.”
  14. Johnson EW. The myth of skeletal muscle spasm. Am J Phys Med Rehabil. 1989 Feb;68(1):1–1. PubMed 2521794 ❐ PainSci Bibliography 56710 ❐
  15. Maigne JY, Cornelis P, Chatellier G. Lower back pain and neck pain: is it possible to identify the painful side by palpation only? Ann Phys Rehabil Med. 2012 Mar;55(2):103–11. PubMed 22341057 ❐ PainSci Bibliography 54321 ❐

    Researchers tested two (presumably expert) examiners to see if they could detect the painful side of the neck or back by touch alone, feeling for tension in the spinal muscles. In almost two hundred patients, they identified the correct side of 65% of lower back pain and just 59% of neck pain — only slightly better than chance.

    The results are underwhelming. Although they did a little better than just guessing, the results suggest that it’s difficult even for expert examiners to detect the location of neck and back pain by feel. As well, they were only attempting to detect the side of pain. Imagine how much worse their performance would have been if they’d had to identify the location more precisely, or if the pain could have been anywhere or nowhere. So they barely passed the easiest possible test, and probably would have failed a harder one and done no better than guessing.

    An obvious weakness of the study is that only two therapists were tested, and so the results are inconclusive. One would still hope for a better detection, though, even from less skilled therapists.

  16. Spasm could be fairly evenly distributed, but probably not so much that it would fool experienced massage therapists. Most neck pain is strikingly one-sided, and it’s unlikely that related spasming would be tidily symmetrical.
  17. If common body pains were in fact substantially caused by spasm, then it seems like either massage should be an extremely effective treatment, which it clearly is not … or massage is not actually good at reducing muscle tone, which would really upset a lot of massage therapists! But I’m not issuing any kind of a ruling here: it’s just an interesting perspective to consider.
  18. Enke O, New HA, New CH, et al. Anticonvulsants in the treatment of low back pain and lumbar radicular pain: a systematic review and meta-analysis. CMAJ. 2018 Jul;190(26):E786–E793. PubMed 29970367 ❐ PainSci Bibliography 53209 ❐

    This review of 9 trials gives two thumbs down for anticonvulsants (gabapentin, pregabalin) for back pain, sciatica, cranky nerve roots. And there are risks. I know this will shock you, but apparently these drugs have some side effects.

  19. Szeto GPY, Straker LM, O’Sullivan PB. Neck-shoulder muscle activity in general and task-specific resting postures of symptomatic computer users with chronic neck pain. Man Ther. 2009 Jun;14(3):338–45. PubMed 18606558 ❐

    This simple study showed that muscle tension in the neck is high in patients with neck pain when they rest their hands on a keyboard or type. The study does not show causation: the muscle tension may be a response to pain, and/or the pain might be caused or aggravated by the tension. However, the muscle is unquestionably more active.

  20. Nederhand MJ, Hermens HJ, Ijzerman MJ, Groothuis KGM, Turk DC. The effect of fear of movement on muscle activation in posttraumatic neck pain disability. Clinical Journal of Pain. 2006 Jul-Aug;22(6):519–525. PubMed 16788337 ❐

    This study of whiplash patients showed that muscle tone is inhibited, not increased, let alone spasmed. “It is likely that the decrease in muscle activation level is aimed at ‘avoiding’ the use of painful muscles.”

  21. [Internet]. Levin SM. Muscles at Rest; [cited 20 Feb 17]. PainSci Bibliography 52508 ❐
  22. Minetto MA, Holobar A, Botter A, Farina D. Origin and Development of Muscle Cramps. Exerc Sport Sci Rev. 2013 Jan;41(1):3–10. PubMed 23038243 ❐ PainSci Bibliography 54733 ❐ “Dehydration (and/or cramps, motor unit action potentials, motor neurons electrolyte depletion) often is given as an explanation for muscle cramps occurring in workers and athletes, although this claim is not supported by scientific evidence.” And indeed it is contradicted by some good science — see next note.
  23. Schwellnus MP, Drew N, Collins M. Increased running speed and previous cramps rather than dehydration or serum sodium changes predict exercise-associated muscle cramping: a prospective cohort study in 210 Ironman triathletes. Br J Sports Med. 2011 Jun;45(8):650–6. PubMed 21148567 ❐

    Blood samples from 210 Ironman triathletes were checked for electrolytes and other signs of hydration status. 43 had suffered cramps. There were no significant differences between the crampers and the non-crampers in any of the pre-testing or post-testing. Dehydration and electrolyte shortage don’t cause cramps — intense effort does. “The results from this study add to the evidence that dehydration and altered serum electrolyte balance are not causes for exercise-associated muscle cramps.” This is a nice myth-mangler of a paper.

  24. If acute dehydration during exertion isn’t the cause of exertional cramps, could subtle dehydration be the problem? Or could it cause non-exertional cramps? It seems unlikely. If acute dehydration doesn’t cause cramps, why would slight dehydration? It’s not inconceivable, but I don’t see much reason to suspect it either. I think people are only concerned about this as a seemingly logical extension of the common but totally bogus fear of chronic dehydration.
  25. Garrison SR, Korownyk CS, Kolber MR, et al. Magnesium for skeletal muscle cramps. Cochrane Database Syst Rev. 2020 09;9:CD009402. PubMed 32956536 ❐ PainSci Bibliography 52162 ❐
  26. Opar DA, Williams MD, Shield AJ. Hamstring strain injuries: factors that lead to injury and re-injury. Sports Med. 2012 Mar;42(3):209–26. PubMed 22239734 ❐
  27. Minetto 2013, op. cit. There’s a lot of complicated evidence on this, but it is clear that cramping is greatly reduced by nerve-blocks, cutting the muscle off from the central nervous sytem.
  28. [Internet]. Kolata G. Finding May Solve Riddle of Fatigue in Muscles; 2008 Feb 12 [cited 15 Feb 20]. PainSci Bibliography 55656 ❐

    One of the great unanswered questions in physiology is why muscles get tired. The experience is universal, common to creatures that have muscles, but the answer has been elusive until now.

    Scientists at Columbia say they have not only come up with an answer, but have also devised, for mice, an experimental drug that can revive the animals and let them keep running long after they would normally flop down in exhaustion.

    For decades, muscle fatigue had been largely ignored or misunderstood. Leading physiology textbooks did not even try to offer a mechanism, said Dr. Andrew Marks, principal investigator of the new study. A popular theory, that muscles become tired because they release lactic acid, was discredited not long ago.

  29. The mean is always there, waiting to be regressed to!
  30. My quads ripple across a large area of muscle, continuous when contracting, more prominent when fatigued but not dramatically, easily palpable, clearly visible only with the right lighting. I cannot actually feel it, unless I touch it. If it has any effect on performance, I can’t detect it: I seem to be strong and fatigue-resistant in the quads. I’ve had this for years at least, but I’m not sure how far back it goes. I’m not sure if it was always there and I just started noticing it, or if I’ve started noticing it because it’s there more. I am generally prone to cramps and fasciculations and always have been — it’s one of the reasons I wrote this article, and this entire website.
  31. They are the king of weird, annoying spasms — one of the most familiar of dozens of kinds of unwanted muscle contractions, most of which we don’t understand and/or can’t treat (and some of which are painful). They are also probably a common symptom of some systemic health issues (e.g. Mast Cell Activation Syndrome (MCAS)).
  32. Get your mind out of the gutter! Obviously, I am talking about how infants suckle. Pacifiers are, apparently, a popular remedy for babies. It would be interesting to know how a pacifier would compare to the Hiccaway in adults. Since there’s much less swallowing, it might be inferior — but the same mechanism could be at work.

    (Thanks to reader TF for this perspective: I am cribbing from her excellent notes on the topic.)

    Infants start hiccuping in the womb, and it may be part of a critical developmental process. Like so much that seems “wrong” with biology, adult hiccups may just be the price we pay for something we literally cannot live without.

  33. Alvarez J, Anderson JM, Snyder PL, et al. Evaluation of the Forced Inspiratory Suction and Swallow Tool to Stop Hiccups. JAMA Netw Open. 2021 06;4(6):e2113933. PubMed 34143196 ❐ PainSci Bibliography 51364 ❐

    This is a small and low quality positive “trial” of Hiccaway device for hiccup treatment based on questionnaire data from 250 people, with 90% of respondents declaring the Hiccaway to be superior to other home remedies.

    • The mechanism is plausible. Normally when I scoff at a weak trial, it’s because it’s barely positive evidence for something that was kind of a reach in the first place.
    • This is not a “barely” positive trial: it’s strongly positive, a full-power thumbs up, a hands-down winner. And why isn’t that too good to be true? Well…
    • The stakes are low. It’s not all that extraordinary claim, so it doesn’t need extraordinary evidence. The bar is lower. Just like a small study can easily show that soap is slippery, a small study can show that there is a way to stop hiccups.
    • Straightforward outcomes are easier to test for, and hiccups are straightforward: you have them, or you don’t. No one’s being temporarily fooled into thinking that they don’t have the hiccups. (Which happens all the time with trials of pain treatments.)
  34. I feel a bit uneasy about this endorsement, but it just seems so definitive: I simply have not been bothered by hiccups since it came into my life.

    Before: Hiccups were actually a frustrating problem from me, significant because they often interfered with sleep. I tend to get hiccups at night.

    After: No more problem. I simply don’t seem to have to worry about hiccups any more.

    Over the years, I have tried dozens of treatment gadgets and nostrums for pain, and not one of them has ever worked even half as well for me as this hiccup cure. (Indeed, I’m hard pressed to think of one that has worked at all.)

  35. In light of the potential role of hiccups in development fetal and infant development — see earlier footnote attached to “I think I’ve said enough” — it’s entirely possible that they just a completely different phenomenon than another kinds of cramps.
  36. See S, Ginzburg R. Choosing a skeletal muscle relaxant. Am Fam Physician. 2008 Aug;78(3):365–70. PubMed 18711953 ❐ PainSci Bibliography 55418 ❐ “…these drugs have not been proven to be superior to acetaminophen or nonsteroidal anti-inflammatory drugs for low back pain.”
  37. Khwaja SM, Minnerop M, Singer AJ. Comparison of ibuprofen, cyclobenzaprine or both in patients with acute cervical strain: a randomized controlled trial. Canadian Journal of Emergency Medical Care. 2010 Jan;12(1):39–44. PubMed 20078917 ❐

    A study in the Canadian Journal of Emergency Medical Care compared ibuprofen and a muscle relaxant (cyclobenzaprine or Flexeril) for patients with serious soft-tissue injury in the neck. Groups of about 20 patients received one, the other, or both. Results were statistically identical for all patients. This test showed no benefit to using or adding a muscle relaxant for acute muscle strain in the neck. The study is too small to be powerful, but it certainly shows that there’s no strong advantage to muscle relaxants in a situation where they are often assumed to be an important medication, and the results are consistent with other research results.

  38. Flaten MA, Simonsen T, Olsen H. Drug-related information generates placebo and nocebo responses that modify the drug response. Psychosom Med. 1999;61(2):250–5. PubMed 10204979 ❐

    How much does the effect of a medication depend on what you are told about it? Quite a bit, apparently! This strange and fascinating study in Psychosomatic Medicine showed that a muscle relaxant actually increases tension when the patient is told (lied to) that it is actually a stimulant. The false information is so potent — or the drug is so weak — that its intended effect is actually reversed.

    It’s like a Jedi mind trick. These aren’t the drugs you’re looking for.

    But the reverse was not true: even when told that they were taking a muscle relaxant (and they were), subjects did not actually relax any more than people taking a placebo … and in some cases less!

    And there’s more. This study contains many odd gems, such as the bizarre fact that quite a lot more muscle relaxant was found in the blood of people who had been told that the muscle relaxant was a muscle relaxant. It appears that they literally soaked up more of the stuff from the GI tract when they believed that it was a relaxant! And yet it still didn’t actually relax them any more than a placebo.

  39. [Internet]. Ingraham P. A Story of Benzodiazepine Withdrawal Gone Horribly Wrong; 2016 Sep 12 [cited 19 Nov 21]. PainSci Bibliography 52678 ❐
  40. Clostridium botulinum is a bacterium that produces, as a metabolic waste product, a really nasty toxin, among the most poisonous substances in the world. Yikes! Think of that bacteria like a microscopic frog, exuding deadly slime through its skin. It works by blocking the neurotransmitter acetylcholine — the messenger molecule that flows from nerve endings to muscle cells to initiate muscle contraction. The toxin clogs the outlet for the release of acetylcholine molecule from the pre-synaptic membrane.

  41. Not to minimize the suffering that rogue muscle contractions can cause, and certainly some cases are not minor by any reckoning. But most are much less serious than truly dire medical problems, and a treatment with significant risks is probably not a great idea.
  42. Witmanowski H, Błochowiak K. The whole truth about botulinum toxin - a review. Postepy Dermatol Alergol. 2020 Dec;37(6):853–861. PubMed 33603602 ❐ PainSci Bibliography 51239 ❐ “The frequency of serious side effects is 33 times higher for therapeutic than for cosmetic cases.”
  43. Mullaaziz D, Kaptanoğlu A. Is botulinum toxin a cause or a cure for headaches? J Cosmet Dermatol. 2022 Feb;21(2):595–599. PubMed 34897957 ❐ (Witmanowski et al. also discuss this.)
  44. Guo X, Li T, Wang Y, Jin X. Sub-acute hypersensitive reaction to botulinum toxin type A following Covid-19 vaccination: Case report and literature review. Medicine (Baltimore). 2021 Dec;100(49):e27787. PubMed 34889230 ❐ PainSci Bibliography 51236 ❐
  45. Sun LC, Chen R, Fu C, et al. Efficacy and Safety of Botulinum Toxin Type A for Limb Spasticity after Stroke: A Meta-Analysis of Randomized Controlled Trials. Biomed Res Int. 2019;2019:8329306. PubMed 31080830 ❐ PainSci Bibliography 52066 ❐


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