Re: right way of doing sitting kokyu-ho
In sitting kokyu-ho, usually there's a tendency to grab very strong and hold the wrists down, so Uke doesn't let Tory perform the movement. If Uke is pressing down there are ways to perform a technique and break his/her balance.
But we must remember that Kokyu-ho is not an exercise to train the strength of the arms, but an exercise to train the center/balance. So in the BASIC kokyu-ho, Uke doesn't press down, because in this fashion, he/she only controls Tory's arms, but doesn't affect Tory's center/balance. Uke should grab the wrists and press forward, with the intention of breaking Tori's balance (push Tori in his back).
From this situation, Tori has to redirect Uke's force, keeping a balanced center, redirecting Uke's force up, with the kokyu-ho movement, and the is Tori who is able to breack Uke's balance. Remember. It is not for training muscular strength, it is for training the center.
If Tory is correctly centered and balanced (pressing his/her center forward and down) he/she should be able to resist Uke's push, no matter how strong he/she pushes. Now, this has nothing to do with magic or some kind of mystical force; it's just physics. As Uke pushes forward, Tory channels this strength through his/her body towards the ground, making him/her very hard to move.
Now to unbalance Uke, Tory should keep pressing his/her center forward and down, but his/her arms make 2 important movements to take Uke off balance:
1 A circular movement forward and up from the shoulder
2 A rotational movement from the elbow up to the hand, so the palm of Tory's hand face Uke (with this movement one could bend the elbows a little to help take Uke's center up)
These movements should take Uke up and off balance, so now Tory keeps pressing forward from the center (keeping the center low) and to the side he/she chooses to throw Uke.
Aikido Goshin Dojo