Re: does nikyo hurt?
@ Walter and Jon,
I think we are talking about very different things. No, I wouldn't trust my life to a non-painful nikajo the way we perform it in the dojo. However, I wouldn't trust my life to nikajo under any circumstances.
"Controlling" uke has different meanings. In the kenshusei program in Kyoto, everything we are doing is about learning how to use our own center and get control of uke's center. In that training context, nikajo/nikyo can definitely be done to control uke without pain. I have had it done to me. I couldn't really resist--I just crumpled onto the ground. Would it have worked if I had been full of adrenaline and trying to punch and kick and shite and my bodies weren't aligned properly? Probably not. That is not the point of aikido, though, in my opinion.
Eventually, at a higher level of performance, I think the lessons learned in aikido should translate into improved fighting. However, if all you want to do is learn self-defense techniques, then you are wasting a lot of time in an aikido dojo, when you could be just learning only the most effective take-downs and locks with the most "wiggle room" for street-brawl-conditions-error.