involuntary movement, semi-involuntary movement, kriyas:

In meditation, sometimes one might go through periods of having involuntary movements (as distinct from sort of finding oneself sort of involuntarily inclining into different postures or body positions, and also as distinct from muscle tension, but/though all of which have pretty similar deep causes).

Involuntary movement can be arm movements, hand movements, head movements, shoulder movements, full body movements like arching of the back, eye movements, pretty much anything. Sometimes vocalization is a thing. Sometimes it's repetitive rocking or turning, sometimes it's more isolated and intermittent twitching or jerking.

Sometimes it can catch one by surprise and so be quite involuntary. Other times, because it's more rhythmic, one can incline towards gently, experimentally suppressing or quelling it, but as soon as one sort of semi-forgets about it, and attention goes a bit elsewhere, the movement will start up again, for a time.

As with lots of phenomena, questions that come up a lot with involuntary movement are, (a) is this a thing (for other people or in general)?, (b) what's causing this?, and (c) is it good or bad? (or, is it an indicator of progress?).

We'll mostly only focus on the latter question, here, though the other questions may be partially answered somewhat incidentally.

As an answer to "is it good or bad," as a general theme in this book, the answer, here, too, is, it depends.

(a) Sometimes movement is part of "redo to undo," and so it's "good." This can include some repetitive-seeming movements.

(b) Sometimes movement that is sort of repetitive means something is "stuck," like the body is trying to "compute out" something with movement but it can't quite complete the calculation. In this case one might consider this "neutral" or "bad." (As per usual, big scare quotes on "bad.")

(c) Sometimes movement, repetitive or otherwise is because other parts of the system are getting "squeezed" and so the movement is sort of "pressure release." I think in these cases, this is more likely to indicate entrenchment/burn-in, or at least loss of slack elsewhere but with a twist still remaining, and so this is "bad."

(d) Sometimes movement that looks a lot like (previous) (b) or (c) is actually (a). That is, one starts out with movement that's stuck or entrenching, but, in seconds, minutes, hours, or months, the system figures out how that that prior movement was counterproductive, and so repeats it to undo whatever the suboptimality was.

But, as per usual, it can be hard to tell which of these is going on at any given time, in part because it can often be a mixture of one or more, including all four, going on at once.

Do note, not all suboptimal movement needs to overtly redone as per redo to unto. There can be "liminal redo to undo" even when movements were very large and overt. That said, some overt movement, for some people, will eventually need to repeat itself, intermittently over weeks or months, at some point during the three to five to seven to ten to twenty to thirty years of the path (depending on how much time or resources a person has to meditate and how amenable one's system is to high temporal density practice, on average, etc.). Sometimes this is just a little bit and sometimes it's an almost "exhaustive" replay, though not necessarily all at once. It might come and go over months or even years.

In terms of generalities:

So, in general, maybe, if someone is experiencing a tiny bit of movement, fairly regularly, then this is a weak positive lead indicator.

If someone is experiencing a lot of movement early-to-intermediate, I consider this a weak indicator that someone might benefit from exploration of their models of practice.

If someone is experiencing a lot of "high-amplitude" movement "late" in their practice, in a meditation system that doesn't have something vaguely like global wayfinding, I consider this maybe a medium indicator that their practice took a wrong turn somewhere and they would have a decently long way to go, still (and maybe still heading partially in the wrong direction with a lot of momentum, as it were--and I'd then also be on the lookout (especially but not assuming it's necessarily definitely there, or anything, and it might not outside-view/observationally useful, in any case) for possible behavioral/cognitive/emotional rigidity or suppression and other issues such as lots of reduced slack). And not to reify or pass judgment on on of this, in a vacuum, all of this subject to outside-view provisionality and the limitations of anemic, vague, or abstract concepts, and, etc.)

If someone is experiencing a lot of low-amplitude movement (and maybe a tiny bit of high-amplitude movement); (especially that maybe keeps coming back but is interleaved with lots of other things), medium-to-late in practice, in a meditation system that has something vaguely or explicitly like global wayfinding, I would consider that a neutral-to-positive indicator, and first-pass assume that their practice was going fine, and I wouldn't be especially worried or find it remarkable or even notice, at all, if they had counterfactually reported no movement.

In any case, there are exceptions to all of this. It'll depend very much on the contingencies of that person's system, including earlier life experiences and the types of practices they might have previously engaged in.

In general, over time, nonmonotonically, movement becomes less and lower amplitude, more shimmery, people general become more still when not overtly moving, though not in a suppress-y way (and, for what it's worth, late stage, at the time of this writing, I change positions all the time, for comfort and self-care, and I jiggle a leg a little bit, or whatever, if I'm a bit too much in caloric surplus).