Sensible advice for aches, pains & injuries

Cramps, Spasms, Tremors & Twitches

The biology and treatment of unwanted muscle contractions

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

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 several major types of unwanted contractions:

Twitching and tremors rarely indicate a serious problem

Nearly all twitches and tremors are harmless and will never be explained. They are classic “non-specific” symptom with endless possible causes (like fatigue or malaise). Unlike 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 things 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 …
  3. 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 balancing act that gets a little off kilter surprisingly often. There are also so many checks and balances that it’s harder to throw it off a lot. This may be why unwanted contractions are so common and yet usually meaningless.

What about “spasms” as in “my back is spasming”? The myth of painful spasms

Weirdly, there is no such thing as painful sustained muscle contractions, or back pain caused by cramping. (This is just the first of a few myths this article will cover.) Painful contractions all fit into one of the descriptions above, like exertional cramps or neuropathic spasticity. They don’t just randomly happen to otherwise healthy people.

And yet, for decades, unexplained musculoskeletal pain — especially back pain — has been widely, carelessly attributed to “spasms” by practically everyone: a goofy non-diagnosis with strong emotional appeal to both doctors and patients, cynically exploited by pharmaceutical companies to sell a treatment (muscle relaxants).4 It’s appealing because it’s simple, and because a lot of body pain feels like a spasm, probably because some strong contractions may occur in the presence of pain that has other causes.

So what does cause sharp back pains?

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 Save Yourself from Low Back Pain!).

Sudden-onset back pain is definitely a distinct type of back pain, and yet it still has a lot of 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. The reason that back pain often seems spasm-y is 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 stiffness — which is complex, but basically boils down to uncomfortable movement — can also seem like muscle spasm.

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. 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. 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 it5 … 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. It’s important, but 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.

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 unwanted contractions.

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:

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.

The myth of protective muscle spasm (aka “muscle splinting”)

Contrary to nearly universal belief, the body mostly does not react to trauma by immobilizing the area with a “protective” muscle spasm, also often called muscle splinting. And there’s another myth built on the back of that one: the belief that this leads to a vicious cycle in which spasm causes more pain, the “pain-spasm-pain” cycle. Together, “protective spasm” and “pain-spasm-pain” are two of the classic myths of neck and back pain, and a great many patients have heard these explanations for their pain from professionals.

Injury probably inhibits muscle contraction78 — protecting the injured area more by shutting it down than by tightening it up, neurological “lock down” that feels like spasm, but it’s really just a strict, powerful command from the CNS: “DO NOT #%[email protected]!$ MOVE THAT.”

Strong contraction would be very dangerous for damaged tissues — obvious if you stop to think about it.

“But I feel so stiff!” you might protest. “It feels like spasm.” Yes, it does: but stiffness is a sensation, a cousin of pain, not a 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.

The old concept of a pain-spasm-pain cycle does not stand up to experimental verification either from a physiologic point of view or from a clinical point of view.

Physiologic studies show that muscle pain tends to inhibit, not facilitate, reflex contractile activity of the same muscle ...

In 1989, Ernest Johnson, editor of the American Journal of Physical Medicine, summarized overwhelming evidence that the common perception of muscle pain being closely related to muscle spasm is a myth and that the myth has been strongly encouraged by commercial interests.

~ Muscle pain, by Siegfried Mense, David G Simons, and IJ Russell, p. 259

These myths are not so bad as myths go, more interesting than scandalous, more like misleading oversimplifications than capital-M myths. Exactly how muscle behaves in the aftermath of a trauma depends on many different factors, such as the severity, type and location of trauma. Muscle is de-activated in response to severe fractures, for instance, because it really doesn’t make much physiological sense to spasm when pulling on broken bone.

If gross spasm was a factor in neck pain, for instance, it should be easy for experienced professionals to feel it. In one test of this skill, two doctors (trained in manual medicine) could not even identify the side of the body that neck pain was on by feel alone910 — which is rather disappointing. If there is spasm, it can’t be much.

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 true, pure, and long-lasting spasm is virtually unheard of. I have had my hands on thousands of patients with painful backs and necks, and “spasm” is just not an accurate description for any of them. High muscle tone and a hardened, ropy texture seem to be common, and this impression is supported by good evidence.11 But “spasm”? It really just doesn’t happen. And, even if it did, it wouldn’t be a “pain-spasm-pain” cycle.

Exercise-induced cramps (and yet another myth)

Infamously for those who have followed performance science over the last 20 years or so, cramps are not caused by electrolyte loss or dehydration,1213 acute or chronic.14 What actually does cause them is still unclear (shocker): all that really is clear is that it happens in very fatigued muscles. Ironically, muscle fatigue is also something of a biological mystery!15

Strains or “pulled muscles” can occur without any fatigue at all, but they do occur more often when you’re fatigued.16 (So do many other injuries, of course.) And cramps can occasionally be so powerful that they tear muscle, though usually not very badly.

Hotshot in the dark: a spicy new cramp treatment?

Biologically plausible? Check. Credible scientists on board? Check. Actually tested? Um…

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. 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.”17

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,18 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 most controversial contraction: the trigger points

This section is a brief summary of a topic I’ve covered ad infinitum and ad nauseum elsewhere. If you’re a professional, start with my review of trigger point science. If you’re a patient, start with my basic self-massage primer.

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.

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.

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.

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

2017Added 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.

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

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

2017Major 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!



  1. I had a twitching muscle in my back for eight months in 2014. It was probably the latissimus dorsi. These were fairly strong contractions that would sustain for 10-30 minutes at a time, several times per week, often disrupting sleep. This was frustrating and worrisome, but eventually that particular twitch simply went away, and I have never felt it again since. Unfortunately, it was the worst of many others. I seem to be prone to fasciculations, which is one of the reasons I wrote this article. BACK TO TEXT
  2. 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. BACK TO TEXT
  3. The disease “tetanus,” AKA lockjaw, is an infection with the bacterium Clostridium tetani, which causes powerful cramps. BACK TO TEXT
  4. Johnson EW. The myth of skeletal muscle spasm. Am J Phys Med Rehabil. 1989 Feb;68(1):1–1. PubMed #2521794. PainSci #56710. In this editorial from 1989, Dr. Johnson decries the “preposterous” spasm diagnosis, describing “overwhelming evidence that skeletal muscle spasm is nonexistent.” Although I agree, I wish I knew what “overwhelming evidence” debunks the myth: he only mentions one 1950 study that I can’t find, and a replication of it that he was involved in that I also cannot find. 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.” BACK TO TEXT
  5. 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. BACK TO TEXT
  6. Specifically, we still don’t know if it’s a neurological phenomenon, or if the tissue physically changes, or both. BACK TO TEXT
  7. Nederhand MJ, Hermens HJ, Ijzerman MJ, Groothuis KG, 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.”

  8. Most of this section is based on this idea, but I haven’t supported it thoroughly yet. More citations needed!” It’s a high priority for future updates. BACK TO TEXT
  9. 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 #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 had 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.

  10. 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. BACK TO TEXT
  11. Szeto GP, 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.

  12. 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 #54733.


    Cramps are sudden, involuntary, painful muscle contractions. Their pathophysiology remains poorly understood. One hypothesis is that cramps result from changes in motor neuron excitability (central origin). Another hypothesis is that they result from spontaneous discharges of the motor nerves (peripheral origin). The central origin hypothesis has been supported by recent experimental findings, whose implications for understanding cramp contractions are discussed.

  13. 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 was no significant differences between the crampers and the non-crampers in any of the pre-testing or post-testing. The shocking conclusion? 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 EAMC.” A nice myth-mangler of a study!

  14. 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. BACK TO TEXT
  15. [Internet]. Kolata G. Finding May Solve Riddle of Fatigue in Muscles; 2008 Feb 12 [cited 15 Feb 20].

    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.

  16. 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. BACK TO TEXT
  17. The mean is always there, waiting to be regressed to! BACK TO TEXT
  18. My rippling quads affects 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. BACK TO TEXT