i'd be interested in knowing where the studies of yonkyo as periosteal pain can be found...if that were the case, then pressure anywhere on bones of sensitive individuals would cause the same pain, and i'm told the feelings are distinctly different...and since one most often pointed to area of pain is where, as others have said, the radial nerve usually passes, i'd like to see what those articles have to say.
Dr. Greg Olson did the series in "Perceptual & Motor Skills" (71(3 Pt 2):1059-66, 1990 Dec. for the yonkyo)
Eckert and Lee did a follow-up on nikyo, where they discuss the periosteal pain. (same journal, Dec 1993.
My wife's the Doc, anatomy professor, and Medical Examiner; she tends towards the periostial pain side of the argument.