I don't think one needs to try to get that detailed into mechanism. Why not just say "it changes the way you expect your body and muscles to move, you don't consciously run all your muscles all the time but instead rely on automatics, and between that and the fact that the interplay between our overgrown thermostat of a brain and the body it is a part of is so close expectations actually matter especially with motion"?

I wanted to mention something like this as a stage trick. I was not sure if it is done globally. An aikidoka friend of mine has formed an O with his thumb and index finger and asked me to pull it apart. He did not seem to be pressing them together hard at all, yet I could not even though I an fairly strong. He explained he was visualizing his fingers turning into an iron ring. I still don't understand how this can work. My best guess is 1) with lots of visualization practice he convinced himself 100% 2) due to his confident body language I doubted myself and my strength was sapped.

EDIT: wait, I found it online! http://bodymindandmodem.com/CoolKi/Finger.html

More tricks: http://bodymindandmodem.com/CoolKi/CoolKi.html

Thanks for the idea, this is what I meant by cool stage tricks.

EDIT2: possible explanation: http://aikidoforbeginners.blogspot.com/2007/06/unbendable-arm.html