Isn’t there too much lumbar rotation in the twisting stretch Gray Cook named after Brett Jones?
There is no lumbar rotation with this technique.
If you have your hips locked up and not moving AND you have some cervical or t-spine limitations, it will certainly become lumbar rotary.
However, the verbal cue is to twist as far as your upper back will let you, no further. If you try to get your chest to the floor, you will have to rotate in the lumbar. I would consider that poor form.
I think the strain is bypassing the lumbar spine. It’s like 3 different stretches, and the hand holds and floor are the stability mechanisms.
Static hip extension/knee flexion on the down leg. That alone would yield the lumbar spine into extension.
The hip extension is stabilized by the horizontal ADDuction of the front leg. You become like a buoy. You could probably stop the stretch there, and there should be no lumbar motion. There is strain or influence, but it is blocked by the hand holds. The control of the lumbar spine comes from the control of the motion of the hips.
Then on the top side, the rib roll will only go as far as the t-spine will allow if you maintain the hip position.
There are forces created, absolutely. But they are attenuated by the floor and locking down the hips and keeping them there.
I know when I personally do it this way and when others do it this way, you feel nothing in the lower back. It’s actually an “empty” kind of feeling.