The second was (I think this is what its called) suwari waza ryotetori yonkyo. I was having trouble with technique with my partner and Suganuma Shihan come by to show us. He grabbed me by both my wrists and applied yonkyo. The shock ran up my arms and locked my elbows, I made my best "Popeye" face in agony and fell over backwards. I am one of the people who yonkyo is difficult to apply and Suganuma shihan nailed me as soon as he grabbed me.
Thanks for reminding me - this is one of his signature techniques, and I have no idea how he does it... Here is a one handed version:
As you say, uke has elbows locked, shoulders lifted immediately, and yet Suganuma sensei's wrists are not rigid or seemingly being subjected to huge forces - and yet resistance is futile!
Time for another round of research on this one...