Re: why do people outside Aikido for IS?
If I understand Mary's OP correctly, you're really trying to understand the inner experience that leads someone to look for this kind of training.
Y'know, people say it takes years of all these solo exercises to really develop this stuff and I'm sure that's true. But it doesn't take years to start to see the benefits. Some pictures:
Your teacher says, do this exercise. You do it. Interesting exercise, extending the spine up and down simultaneously, but pretty esoteric. But your teacher says it's important so you practice it every day .
Then a few weeks later, your teacher says, "Remember that exercise? When uke attacks you, do it. Then do the technique."
This is pretty silly. Extending the spine doesn't have anything to do with handling an attack. It doesn't even counter the power uke is putting into the attack. But you do it anyway.
And uke's on the mat.
What? But I didn't do anything!
Katate dori. You're practicing the IS skills.
"You're pushing," says your teacher.
Damn. Drop tension, drop resistance.
"You're still pushing."
Damn again. Where's the tension? There it is. Drop it, let it go.
"Now you're pushing the other way. Relax."
I am relaxed, already! There, let that piece of tension. Connect this to that. Hey, I'm moving naturally--all that tension I didn't know was there is gone. And my teacher is flying across the room.
Huh? But I didn't do anything!