I agree it is interesting, which is why I am engaging in this thread!
I keep wishing that he could cite a reference other than his own experience. Is this a reflection of how ki moves up and down in the body during certain breathing meditations? Does anybody from Ki Society background know if this was ever explicitly discussed, taught or shown by Tohei Sensei?
Niall quite right in pointing out the gist of the thread. For those who find it interesting I have cited a reference they can look up in order to understand what Koshi is and some history of it and indeed how it is used generally within the martial arts. ie: as the pivot and power base and the place from which you move.
As to Tohei? I'd like to know too.
I have taught this for more than ten years and so have a good understanding of what I mean and I'm sure you'll understand that when teaching I don't give references but demonstrate and give exercises for people to do and learn and apply.
Thus I can see when someone is using good Koshi and when they are not. I recall someone pointing out a Shihan who used to say Aikido could be done on one mat. This teacher it is said used to draw shapes, as i recall for instance the letter D and basically the uke would splatt straight down and indeed wouldn't want to feel that again. To me this was an example of the Ki of Koshi or rather both being used, hara and koshi.
So I'm afraid I can only give you what I know and use and any citations which align with it.
As far as Ki and Ki flow through the body during breathing meditations? Well that's a bit of a subject in it'self.
Once again I can only give you my experience gained through solid practice over many years without referring to any references.
Through Ki breathing or meditation you do become aware of filling the body with Ki and also aware of Ki flowing through the body. The breathing analogy is just that to me, an analogy. You may start with physical breathing but in the ned it is the natural flow in and out from centre of Ki.
So from that perspective your question of up and down the body doesn't make sense for it is like saying does air move up and down the lungs.
However from another perspective in my opinion and experience it does.
I can only explain this however in terms of Koshi and Kokyu and maybe add on to that centerline.
Kokyu being universal heavenly Ki and Koshi being infinite earth Ki. Heaven and earth.
Now the connecting line being centreline and the gathering place for the heaven Ki being Hara.
Now you can direct your Ki to go up or down or sideways or circularly through the body if you wish but the best way in my opinion is in and out. So now to explain the difference between Kokyu Ki and Koshi Ki in laymans terms and operational effect.
Kokyu Ki enlivens, invigorates, energises, gives life to. Koshi Ki relaxes, receives, allows, settles.
So it is like the great universal space of love and the infinite void.
Thus more to do with Aikido exercises and waza than with breathing for Koshi can receive any and all force and negativity whilst Ki from hara (collected from kokyu) then takes it's place.
When you sit in seiza and relax the body you will then feel the tension and force in the body go straight down centre line through Koshi to earth. Then via hara you may refill your body with heaven Ki and feel refreshed and replenish it all with Ki breathing.
So there you are. I bet that's quite new for you to hear put in that way. Hopefully you find it interesting or even useful but alas no citations.