On reading through this interesting thread one of Mike's sentences that jumps out at me is:
The point is that Aikido, Taiji, and other arts aren't considered complete without these kinds of skills because their core concepts were designed to work with this form of strength.
I am quite surprised at some aikidoka either not practicing or having little awarenes of unbendable arm ( another description that doesn't really accurately describe what it is! ). For me having been brought up on practicing and testing this exercise since day one, I wonder how do you do aikido without it? It is not a party trick, it is a fundamental basic mind body state central to aikido.
My guess is that those that have practiced 'enough' probably 'have it' anyway.
For those of us who do practice this particular exercise we know that 'un bendable' arm is not an arm that can't be bent!!, it is a mind body state that allows the transfer of forces to be optimised, from the hand/arm to/from the centre/onepoint. It is difficult to gain understanding from a written explanation of this.
Mike did a good job in post # 32, but to understand it you have to practice it, to practice it you have to have the teacher to point you in the right direction and correct you when you inevitably start 'modifying' what he/she has just shown you. Being shown something once and then going off to practice on your own allows any 'missunderstandings' to be habituated, and therefore difficult to change.
just a few thoughts,