This question came up in the Online 10-day Retreat Nov 3, 2020, guided by Delson Armstrong. Day 1 was part of a daily 30-minute discussion on the suttas, the Dhamma talk and reflections.
Slightly edited to improve readability
Movement is a bodily Formation.
I would not say the three Formations are necessarily interwoven. They are categorizations of different experiences that are caused by them.
In the case of mental Formations, they cause the Feeling and Perception. The sensations, the experience within and without the body and mind, and the perceptions that are tied to it.
The physical Formations, generally and traditionally speaking from the suttas, are related to the breath, first and foremost. But there is also the decision-making process arising from that Formation to move a limb, for example. I would also categorize that under the physical Formations, but that is the way I would view it.
The vocal or verbal Formations are really the Formations that arise from your Perception. What I mean by that is; right now, you perceive that I am speaking to you. And you are listening to what I say. In your mind you might start to be making thoughts, as a response to what I’m telling you. So, the perception that you experience in the way of listening and understanding what is spoken, then conditions or activates the Formations, that create or condition the speech that you may have in the way of responding to what I might be telling you.
They are not interconnected, but they arise so quickly, in the way of how Contact arises, that they seem like they may be interwoven.
For example, when you’re in meditation, or when you are just sitting down and you make a body movement, you move a limb. You notice that it also creates thoughts in the mind, or it creates other kinds of mental Formations, but that is caused and conditioned by the Contact. It will actually spurt out, if you will, two different types of Formations. First of all, the physical Formation had already taken place when you moved the limb and as a reaction to that, you had the thought of moving the limb. That created further thought patterns.
These two things are like forks in the road; you started first with moving the limb, but that process was conditioned by a physical Formation. That process of movement didn’t cause or condition or activate a physical Formation; it was the other way around. The other fork in the road is a result of having moved. They are thoughts that arise, based on the mental Formations, that come from the Contact of having moved the limb.