So, I said in a previous post or three that the unbendable arm in aikido is not really unbendable, rather it is the arm that is not supposed to be bent - or perhaps you could think of it as the unbending arm. If you are moving correctly then you should almost never have to bend your arms to do something in aikido.
This makes the arms a great gauge as to whether or not you are moving correctly. When you do a wrist release, do you come to a point where you have to bend your arm or twist your own wrist to fit with uke? If so, you are not in the right place at the right time. So unbendable arm is not a thing that you have to do because that is how it is supposed to be. Rather, you can tell if you are doing everything else right or wrong by paying attention to your arm posture.
Patrick Parker, is a Christian, husband, father, judo and aikido teacher, Program Director for a Cardiac Rehab, and a Ph.D. Contact: firstname.lastname@example.org or phone 601.248.7282