So in doing tekubishindo undo today I felt tingling lines based on where I was trying to activate. I first imagine I'm sucking a pingpong ball into each hand, more or less centrally located, just above the heel of the palm. I expand my palm trying to feel the pull on this "pingpong ball" as I shake up and down above my head. I try to relax whatever begins to feel muscular strain while maintaining the bouncing action. When I throw my hands upward, my body moves up with it, so my whole body is bouncing as part of the movement.
Mentally, I keep coming back to focus on those "pingpong balls" and hara, trying to hold their respective feelings at the same time in my mind.
...Anyway, FWIW. Mine is not even close to an authoritive understanding; just sharing what I'm trying out. My hope is to map out different approaches to these simple exercises, which I believe have deeper ramifications than simply "warming up."
Some supplemental examples I found online:
(@4:10 = tekubi shindo undo)
This is the only one I found which offered some kind of description for application.
Here's an example of tori fune undo followed by something that has similarities to the Chinkon Gyo I've practiced.
Another example including the Chinkon Gyo similar to the Tamura Sensei example.