I am preparing a seminar on the applications of Empi kata, and found myself explaining yet again that the Shotokan back stance is the "new" back stance. Okinawan styles tend to use the "old" back stance, which is on display in Empi, too. The "old" back stance is very simple. You do a standard zenkutsu dachi, and then turn your head and shoulders to the rear. The "swallow block" position of Empi is just an extreme example of it.
Today I got curious and looked to see if the "new" back stance is, in fact, a Shotoism. I spent some time with Google, sifting through a sample of the 34,000 web pages that mention "kokutsu dachi." The "new" back stance is pictured on sites that promote Shotokan, Shotokai, Tae Kwon Do, and Wado Ryu karate. These, as we know, are Shotokan derivative styles. I did not find the "new" back stance in any of the non-Shotokan styles I visited.
If the "new" version is really confined to the Shotokan lineage, then it is likely to be yet another example of something that was changed purely to make katas more difficult and more impressive. When we interpret bunkai, we should experiment with either the "old" back stance or the cat-foot stance (nekoashi dachi) instead of trying to make the "new" kokutsu actually work in any practical way.