I have had many conversations that the biggest influence on Sosai was not Gichin Funakoshi nor Gogen Yamaguchi but was So Nei Chu, who was also Korean. I found a really interesting page on So Nei Chu that I wanted to share with everyone.
When I would go out drinking with my senpai in Tokyo, inevitably stories of Mas Oyama would come up in conversation. Some who trained under him would talk of the inspiration Oyama drew from things he read including legends about ninja. Oyama would read things, then tell his students that we too should be able to do such and such: handstands; handstand walking; stick jumping; extreme pull-up exercises. i've seen such tests administered randomly for shodan exams but not uniformly.