Bill Glasheen wrote:However... The crescent is about several things.
The obvious issue is what George discussed - maintaining the center (without side-to-side movement) while stepping. To the degree that it's only about that, then the decision to crescent - or not - depends a lot on your speed of movement and the degree to which you are willing to telegraph the direction you want to go as you commit to move.
As always, anything I write here on the subject of karate, at which I am at best journeyman and at worst a novice, should be considered a "teaching opportunity".
This is an interesting topic for me because I began my karate training in Matsubayashi-Ryu. Even though I no longer practice that style (except for performing Naihanchi and Passai once in awhile), I still generally try to look for underlying truths that affirm both traditions, especially where they differ. Here, they differ. Matsubayashi-ryu uses a stance with one foot forward is called "natural stance" (shizentai-dachi) where Uechi-ryu uses sanchin. The rear foot at 45 degrees or so and the forward foot facing directly forward. I don't recall anybody needing to use crescent stepping to avoid moving side to side when stepping forward, but of course the stance is narrower to begin with, and the grounded foot is nearer to the center of gravity. With the grounded foot farther to the side in sanchin, some consideration of side-to-side stability is needed if one is not stepping very quickly. When moving very quickly, crescent stepping for balance
makes no sense, which is presumably why we don't do it when lunging into zenkutsu-dachi or the evenly-weighted Uechi long stance (sometimes referred to as kiba-dachi for lack of an official name). So that all makes sense to me. We practice crescent stepping when moving at slow to moderate speeds when stepping from sanchin to sanchin because it corresponds to better balance at those speeds (when stepping from sanchin into sanchin) and
because it corresponds to applications that can take
balance from an opponent when fighting in close.
However, I wonder if just a little too much is made of not moving side-to-side. It seems to me that there is a minimum speed required to avoid it. At a "normal" sanchin stepping speed, the motion of the crescent step is sufficient dynamically
to counteract the loss of the supporting foot without moving the center of gravity more than the slight translation that is implied by the motion of the leg itself. It is therefore unnecessary to translate the pelvis sideways in order to maintain an upright posture. The "kicks/sweeps" in Matsubayashi-ryu's version of Naihanchi kata (e.g., http://www.youtube.com/watch?v=Dk91kI_76jU
) rely on the same dynamic principle. However, the slower the step, the slower the leg moves, the more a static analysis applies, and the static case all too clear. When stepping from sanchin to sanchin, if you're going too slow, you will fall sideways if you fail to shift your center of gravity sideways, and with Naihanchi, if you don't perform that leg motion quickly enough, you will fall down even more quickly. So of course a simple solution is not to do those stepping/kicking motions too slowly, but what I'm getting at is that if you actually do
do them slowly, as with, say, demonstrating for a beginner or performing them with dynamic tension or for whatever reason, I wouldn't think it would be wrong
to do what physics requires.