You notice it in the evening, on the sofa: a spot on your calf moves on its own. You look and see it twitching under the skin. It does not hurt, it does not limit you, but it goes on for minutes, and as soon as you search for it online you find the word you did not want to read.
This article exists to give you the context that search does not.
The figure that changes the perspective
A study published in the American Journal of Physical Medicine and Rehabilitation did something simple and very useful: it took 50 people with no history or sign of neuromuscular disease and recorded the electrical activity of some muscles with needle electromyography.
The result: 94% showed fasciculation potentials in the abductor hallucis, and 60% in the extensor digitorum brevis (Prevalence of denervation in paraspinal and foot intrinsic musculature, Am J Phys Med Rehabil, 2001).
Ninety-four per cent of healthy people. Fasciculations are not an anomaly: they are a background noise of the nervous system that almost everyone has, and that we usually do not notice because we are not looking for it.
A more recent study, using ultrasound instead of a needle, confirmed that fasciculations are commonly seen in the muscles of healthy subjects, from 21 to 82 years of age (Quantitative sonographic evaluation of muscle thickness and fasciculation prevalence in healthy subjects, Muscle & Nerve, 2020).
What really makes the difference
It is not the twitch. It is what accompanies it.
There is a clinical label for this picture, benign fasciculation syndrome, and its definition is explicit on this point: persistent muscle contractions in the absence of a serious underlying disease, and in particular without weakness and without muscle wasting. It is precisely on this that it is distinguished from motor neuron diseases (Benign fasciculation syndrome among health care workers, Georgian Medical News, 2025).
Be careful with a distinction that makes all the difference: in the same study, 33.3% of people with benign fasciculations reported perceived weakness. Perceived, not measured. Feeling that your arm is "less strong" while watching it anxiously is common; the figure that counts is real strength, the kind that is measured: no longer being able to open a jar, a foot that flops, a hand that loses its grip on objects it used to hold.
Why anxiety is not a detail
In that same 2025 work, among those with benign fasciculation syndrome 60% suffered from anxiety, more than half in a severe form, and 33.3% had a diagnosis of depression. The authors note that anxiety and, specifically, the fear of having ALS seem to play a role in the picture, not just be a consequence of it. The study also found that healthcare workers, who know more about those diseases, have a much higher prevalence: 13.9% against 3.0% in the general population.
It is the classic mechanism: the more you know about the serious possibility, the more you search for it; the more you search, the more you notice twitches that have always been there; the more you notice them, the more tension and insomnia increase, and these in turn increase them.
Put without beating about the bush: if you are spending your nights testing the strength of your hands, that behaviour is part of the problem and should be addressed as such.
What makes them more frequent
The factors that appear most often, and that you can check on yourself over two weeks:
- insufficient sleep, which is what almost everyone recognises first;
- caffeine in high amounts, and alcohol;
- intense or unusual physical effort, especially in the days that follow;
- dehydration and salt imbalances, for example after a long activity in the heat;
- stress and anxiety;
- some medicines (it is worth reading the leaflet if the symptom appeared after starting a new one).
It is not a list of culprits to eliminate at all costs: it is a list to look through to see whether there is a thread. Often there is.
When you need a neurologist, not an article
Get seen, without waiting, if along with the twitches there is at least one of these:
- Real loss of strength: you can no longer do something you used to do, and it shows.
- A muscle that has shrunk in volume compared with the opposite side.
- Difficulty speaking or swallowing, a change in voice.
- Significant and widespread cramps together with the fasciculations, getting worse.
- Fasciculations that always stay in the same spot and progressively spread.
- Onset after a trauma, or together with loss of sensation in a specific area.
And I will add one line that is worth as much as the others: if the anxiety about this symptom is taking away your sleep, that alone is reason enough to talk to a doctor. A visit that closes the question is worth more than any reassurance read online, including this one.
What we can do, and what we cannot
We do not make neurological diagnoses, and this kind of picture, when it has a red flag, belongs to the neurologist. What we do, when the problem is instead a muscle that contracts after poorly distributed loads, a tension linked to working posture or poorly managed recovery, is look at how you move and put the load back in order. In a twenty-minute free first consultation we work out together which of the two situations you are in.
If what you feel are instead real, painful cramps, the chapter is different and has its own rules: muscle cramps, why they come and what works.
Sources
- Prevalence of denervation in paraspinal and foot intrinsic musculature. American Journal of Physical Medicine and Rehabilitation, 2001
- Quantitative sonographic evaluation of muscle thickness and fasciculation prevalence in healthy subjects. Muscle & Nerve, 2020
- Benign fasciculation syndrome among health care workers, a single center study. Georgian Medical News, 2025
