I’ve done it for years (though less as I get older). It’s just a nervous habit.
I do this, it’s just a habit I’d say.
Energy + Restlessness. I never do it when I first wake up and I’m still kind of sleepy and I never do it at the end of the day when I’m beat. It’s when I’m wide awake and full of energy that my leg starts bouncing. My leg fails to bounce if I’m concentrating on something like a video game or a movie. If I’m just flipping through a magazine idly my foot gets at it again.
Just posting to say that I initially read the thread title as “Why do people shave their legs while sitting down?”.
I had this mental picture in my head of a woman trying her darndest to balance on one leg while wielding a razor aimed at the other leg. Not a pretty picture.
I don’t shake my legs much when I sit but I do have to cross them in some way. It feels somehow unnatural if I don’t.
I did it for years but found that it annoyed or distracted people so I tried to stop. Now I wiggle my toes a lot and clench and release my thigh muscles. Gives me the movement I need while being less obvious and annoying to others.
Also, Double Zombie! Just can’t keep a jiggling thread down!
I am somewhat anxious and repetitive motion soothes me. But mostly it’s just a habit I’ve always been prone to. I fidget almost non-stop. Eating more causes more fidgeting (and yes, I’m skinny).
I’m not a leg jiggler, but I do weirds thing with my feet, toes, and legs when I’m feeling very restless…which happens more frequently than I’m likely to admit if I had to give a number. I’ll lift up a leg and kick it out, or clench real tight. I’ll wiggle my toes or make them curl. I’ll flex my feet upwards and keep them that way indefinitely (you know, like how you’re supposed to do if you have a charlie horse). I can make my lower body be still with lots of conscious effort, but then the restlessness manifests in body-rocking, hand-flapping, finger wiggling, balling my hands into tight fists, head-shaking…well, you get the idea. The lower limb restlessness is preferable because it’s not as noticeable if I’m sitting at a desk or table. And since my hands and arms are usually occupied when I sitting, the energy will naturally go downwards.
Sometimes medication can cause the kind of restlessness that I have. But I’m not taking those drugs. It has a name–akathisia–and I’m grateful that I now have a name for it instead of “acting and feeling crazy.” It has gotten worse over time, for some reason. But I don’t know what’s causing it, nor what to do to make it go away. So most times I just ignore it when the “feeling” comes and ride it out as stoically as I can.
I’m know very well what conditions it’s associated with. I just try not to think about them.
I’m right up there with standardized test scores, too. And I’m a fidgeter. I just feel the need to do it. Can’t sit still.
At my previous job, I had a fellow cow-orker who shook his legs non-stop. Vigorously. Also, to make this worse, how shall I put this… he was very heavy. It got extremely annoying when you could physically feel his non-stop shaking even when he was seated at the opposite corner of the conference room from you.
In Japanese this is called 貧乏ゆすり(bimbou yusuri), which has no official translation that I can find, so I’ll loosely call it ‘the poor man’s shake.’ There are various theories as to how it came to be named this, including the idea that the action is reminiscent of a poor man shivering in the cold. Or the perhaps apocryphal assertion that loan sharks would shake the legs of borrowers when shaking them down for overdue repayment.
I’m not sure if I do it all the time because I’m not always aware of it. I suppose it’s restlessness. I have a hard time sitting still for long periods. I’m not a good movie or TV watcher. When I’m reading in bed, or anywhere for that matter, I’m usually twirling a strand of my hair in circular motions with my fingers. I also do this while I’m driving. I think that we all make some sort of movement with some part of our bodies while sitting still. Next time that I’m at a meeting at work, I think I’ll observe to see who is doing what.
Me too! Tetris is really good for being read aloud to. 
Keeping the beat with the music in my head.
To those of you who I bug the shit out of: I would like to apologize. I seriously have to consciously think to not do it, as soon as my mind wanders off, it kicks in again without me noticing. You may as well ask me to stop breathing.
I don’t shake my legs, but I wriggle my toes and clench and unclench my knees all the time, depending on the position I’m sitting in. I can stop if I absolutely have to, but not for long without feeling uncomfortable. However, it’s not going to make the seat jiggle and I doubt people really notice it.
My body just doesn’t like being completely still. I also find it difficult not to multitask.
ADD. An earlier poster said the leg bouncing helps the brain focus. This is very true, but difficult to describe.
In “normal ADD mode” I’ll have several things going on in my brain at once. For example right now I have this post, “Reflections” by the supremes, a programming problem from work, and thinking about what I will cook for football this weekend. The different threads are happening pretty much in parallel. One will randomly jump up and become the “primary” thread while the rest are in the background, but all are there.
As you can imagine, this makes having to focus on one thing quite an adventure. The fidgeting replaces these background threads with something that doesn’t require any actual thought. Leg bouncing is one method of fidgeting, and what I’ll usually do if I can’t get my hands on anything. I know a few neat coin/card flourishes. I have a quarter and a deck of cards at my desk at work and am CONSTANTLY doing something with them. I don’t consciously pick what fidget to do, or even to fidget at all - instead I’ll catch myself mindlessly doing it.
One cool thing that happens with ADD is hyperfocus. Sometimes all the threads in my brain will get set on the same task, even to the exclusion of things like smelling food or hearing someone talk to me. It is a 100% complete and total focus. When that happens, I don’t fidget at all.
Cool! You mean correlation, hospital records? I wonder if the percentage of leg-shakers has been increasing. Reduced legroom on long flights might provide enormous evolutionary pressure.
Vaguely similar: people who faint and fall down when viewing splashes of red liquid. Or people who are mysteriously creeped out by the thought of pointy objects approaching their eyes/throat/crotch. Over many millenia they might tend to die less often, leave behind more children. Eventually all humans experience slight nausea when viewing graphic films of eyeballs sliced by razors. Evolution doesn’t plan, it just amplifies.
Now imagine that you’re chewing on a rusty iron bar. Bite down hard!
I asked two doctors and they confirmed 3 normal reasons.
1 - concentrating on something.
2 - weakness (strange, right?)
3 - thinking of sex… not that is something I did not expect. But the doctor was from on these three things.
I think it is to minimize the rigor mortis.
I’ve always wondered how the zombies were able to move around so well. Ignorance fought.
Maybe they should stretch before shambling.