If we are talking about how the body physically works, we are talking about the body as a machine.
There are also aspects of Mental and Spiritual use, but as far as I can see we don't need to get into those just yet, because we can't even agree on body use yet.
I get hung up on this too. Recently I changed my thinking on this when I was actually able to manifest intent to move uke. With no discernable movement on my part and just using intent uke is driven down into the mat. How's the model explain that?
By no discernable movement I mean I did not move, I did not mean to move and I had no intention of moving and I'm pretty sure if viewed from a third party they would not have seen me move. Yet uke is driven down just by 'thought'.
Anybody that tried to explain it to me I'd have laughed (and did) them off as full of BS, hypnotized, colluding or brainwashed, etc.
Really, no way for me to explain it without everyone calling BS and blowing me off (unless you are one of 'them'). Even video would result in the BS flag being thrown.
Only way was for me to be the uke and feel it done to me ... then do some directed body work and then be able to do it myself. Granted I'm not very good and I'm pretty sure I'm not quite able to explain it hands on (as in teach one how to do it) but progress is happening. Some body work and basic conditioning is required as a prerequisite except for the most rudimentry manifestations.
When I'm able to pull it off with 50% success rate I'll look you (Chris Hein) up next time I'm in Fresno (any excuse to break away from the mother in law).
I think this is what Mike Sigman would call a mind directed manipulation of a ground path (jin) - maybe he would not call it that. From what little I know of Mike Sigman I'd say there is more to it than that (Mike always says that anyway). I'm happy to be wrong ... I usually am. I do like whole bananas.