Sometimes muscles contract when they shouldn’t. Sometimes it’s merely weird and annoying, and sometimes it’s painful or even crippling. Although common and often unnerving, odd muscle contractions are rarely medically worrisome. There are several major types of unwanted contractions:
- Exercise-induced cramps are intense, painful contractions that usually strike when fatigued and/or overheated. They are most common in the legs, especially the calves and hamstrings, more rarely the quadriceps. Fatigue and heat are major factors, but not dehydration and electrolyte shortage — that’s a myth.
- Night cramps are a lot like exercise-induced cramps… but without the exercise! They are associated with fatigue from exercise during the day, but have many other possible causes, ranging from drug side effects to disease to iron deficiency. They mostly affect the calves and thighs, but foot arch cramps are much more prevalent with night cramps than exercise-induced cramps.
- “Spasms”, as in “back spasms” are not actually a thing: it’s an informal, non-specific term often used to “explain” musculoskeletal pain.
- Spasticity is like slow-motion cramping, usually caused by neurological diseases: a combination of jumpy reflexes and very tight muscles causing awkward and stiff movement and partial paralysis in severe cases. A good clinical example of spasticity is the “multiple sclerosis hug,” a painful, suffocating spasticity of the trunk muscles that often feels like a tight band around the ribcage.
- Fasciculations (twitches) are small, brief, repetitive contractions. They occur in healthy people all the time — eyelid twitching (blepharospasm) is especially common — usually in isolated episodes like a case of the hiccoughs, sometimes dragging on longer (I had a twitching muscle in my shoulder for eight months in 2014). There are pathological causes as well; if it occurs too much with no pathological explanation, it’s “benign” fasciculation syndrome, but it can be severe in some unlucky people.
- Tremors are a huge category of involuntary muscle activity, ranging the trivial to the disastrous, from teeth chattering in the cold to the wobbles of Parkinson’s Disease. Essential tremor is the largest subcategory and most common of all movement disorders, including lots of harmless episodes in healthy people (often stress induced). Tremors are usually classified as occurring either at rest or when trying to use the muscle.
- Myokymia is fatigue-induced muscle rippling and quivering, which occurs in healthy people occasionally, and pathologically in people with a bad CAV3 gene (“rippling muscle disease”).
- Clonus is rhythmic, muscular contractions and relaxations often seen with spasticity, usually in cases of stroke or spinal cord injury.
- Trigger points (muscle “knots”) are a hypothetical mini-cramp: a small area of muscle tissue that is abnormally contracted, causing a sensitive spot in the muscle associated with aching and stiffness. However, this model of them is speculative, and the pain and sensitivity may have nothing to do with muscle contraction.
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 twitches and tremors tend to freak people out. But they rarely indicate any serious pathology, and are commonly caused by:
- Obvious things like stress, anxiety, fatigue, excessive caffeine and “other” stimulants
- 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.
Speculation: our motor control systems are a bit delicate, and smooth, precise management of our muscles is the result of a miraculous balancing act that’s fairly easy to throw a little off kilter. And yet there are so many amazing checks and balances that it’s much harder to throw them off a lot. This may be why unwanted contractions are so common and yet usually meaningless.
https://www.painscience.com/articles/cramps-spasms-twitches-tremors.php