Thanks for that Jason. That's a fairly clear explanation. Questions that follow your description are: How do you move/raise your arms without using shoulders/shest biceps? What do you move?
Also, how do you "get under" someone if you cannot drop your hips e.g when you are in seiza?
I'd bet that if someone took an electromyogram of the shoulders, chest muscles and biceps (and trapezius) they'd find that the only way you raise your arms (without using swing momentum or outside help) is to engage the muscles. Denervate those muscles, no movement.
I'm at a complete loss about the 'get under' part if you can't lower your centre of mass.