Maybe something chess professionals learned decades ago is relevant. It is hard to win a match against an opponent who is in good physical shape. Hours of concentration where one bad move loses the contest means the body must support the mind. Good posture allows a better flow of blood to the brain and increases stamina. Rodin's statue "The Thinker" shows a horribly contorted body -- wouldn't mind being paired against such a "thinker" in the final round of a chess tournament. Also don't think it's a workable new-fangled "remodified modified Weaver" stance.
The posture for Zen meditation would be ideal before a physical or mental challenge. It brings out calmness, concentration and confidence. (This assumes you are not on a cold stone floor of a Zen temple with young monks beating you with bamboo swords.) And indeed, Frandoc, Masao Abe's writings on Zen are the best available in either English or Japanese. Simple but not easy. I have played my best chess, shot my best scores and done my best professional work when in good physical condition and having cleared the mind through Zen.
