I do wonder what "straining" hands might be in Japanese though... maybe furishibori ie to muster (strength) ... ie marshal kokyu/jin in the body?
Good stuff Dave.
I asked Shishida about this the last time I saw him (since he wrote that article you quoted). The English translation is not so good, but the "straining hands" concept is part of a concept called "tekubi okoshi" or "hands rising". It is seen in Judo as well as Aikido through the use of tegatana. The idea is to break the balance of the attacker at the instant of contact.
Warning: What follows is my limited understanding of what was shown and in no way represents what Shishida may mean were he to answer himself.
In this case he showed it through a double wrist grab, the concept being to relax the arms and body in such a way as to allow its force to travel down ones arm through the body to the ground and then back up through the same path. At the point where the return force reaches the wrist the fingers are splayed, and tegatana is extended upward along the attacker's arms towards his shoulders. This causes his arms to lock out which connects to his shoulders and his spine, raising his whole body.
The trick to this is the timing of when to splay the fingers and extend into ones partner. There is also the aspect of relaxing and coordinating the whole body so that the rebound force is not lost or does not dissipate somewhere in ones own muscular structure.The force that is extended can be amplified within the body coming from the legs, waist and tanden through the spine and into the arms.
He also showed the reverse effect which through total relaxation projected downwards through tegatana disrupts balance downwards on contact, collapsing the attacker down upon himself or drawing him in towards your feet..
A few months later I read what Ellis said about Aikiage and Aikisage in HIPS and got an "aha" moment. I also found a thread on Aikiweb here - http://www.aikiweb.com/forums/showthread.php?t=16734
that has some interesting info on that side of things.
Finally, there is a clip of Nariyama Shihan that to me shows a bit of the concept as well. It is here - http://www.youtube.com/watch?v=c1QAv0FIQyE
. The one Shishida showed however used a lot less body movement.
Just my 2 cents.