Hi! :- )
The original article is this one, http://detectovision.com/?p=1073
, in which we discuss the strain to Felix' pronator teres muscle.
In baseball pitching, it is considered a given that supination (rotating your right hand clockwise when throwing a "slider" curving fastball) is dangerous, and that pronation (rotating your right hand counter-clockwise, as when throwing a "circle change" offspeed pitch) is not.
Football coaches also teach quarterbacks to throw the (heavier) ball with a pronating movement, though they may be a little vague as to why.
Supination occurs for the uke in the kotegaeshi movement; pronation is illustrated in sankyo.
The question is baseball is *why* this should be the case -- why rotating your R hand counter-clockwise is safe for a pitcher, whereas rotating it clockwise produces a huge number of elbow surgeries.
State-of-the-art motion research in baseball has reached a consensus on the *results* of pronation vs supination -- that is, the results of long-term supination are harmful, and that the results of long-term pronation are not. However, researchers at HSMI, etc., are not clear as to why this is the case.
Felix Hernandez strained the muscle that rotates the R hand counter-clockwise, in the "sankyo" type movement. In loose terms, you might say that he was "performing sankyo on himself" a bit too aggressively as he delivered his pitches.
This is welcome news to Mariners fans, since he is staying away from the slider motion that in effect "performs kotegaeshi" on oneself. (This was the thrust of the original article linked above.)
And the result was merely a fatigued muscle, as opposed to (with over-supination) a torn ligament and "Tommy John" UCL replacement surgery.
A physical therapist pointed out, in comments to the article above, that the rest of the body is much more friendly to a sankyo motion than to a kotegaeshi motion, although he did not phrase it in those terms.
This is self-evident. If you stand with hands at your sides, and raise both arms naturally, of course both thumbs point at the sky....
If from this natural "default" position you rotate your R hand clockwise, as you know, we have only about 90 degrees of comfortable motion; if counter-clockwise, we have at least 180 degrees of comfortable motion.
Even more to the point, the body obviously accommodates OVER-rotation differently in sankyo and kotegaeshi. In kotegaeshi, when one's wrist is turned out even a bit too far, immediately one has to take a quite-unnatural ukemi in order to avoid catastrophic injury. On the other hand, as sankyo is applied aggressively, the entire body cooperates more harmoniously to accommodate the pressure applied by nage (hara floating, shoulders rotating naturally, etc).
The ways in which the hara responds to an aggressive sankyo pin, vs the hara's reaction an aggressive kotegaeshi waza, provides a partial answer as to why pronation is safer for baseball pitchers than is supination. The body "blends" :- ) more easily with pronation.
As is frequently the case, a baffling puzzle in another sport is simply and easily resolved by the insight that aikido offers. Japanese baseball players have always been friendly with aikidoka. Sadaharu Oh, who holds the alltime home run record in Japan, went to O-Sensei for instruction.
Baseball researchers might spend the next twenty years trying to figure out why pronation is safer than supination, or they might go ask an aikidoka what is going on in the throwing movement. ;- )