I mentioned the arch but I didn't know if Kitty was talking about the same arch. The whole forearm is in the form of an arch. It is not structurally an arch like the bones of the feet or the pelvis arch but it is close enough. You can see it better by placing your whole forearm at the side of a table so that elbow and tips of the fingers rest on the same plane. Fingersa and elbow are the pillars of the arch and wrist is the is the apex.

If the wrist is the apex of your arch, what role do the knuckles play - or is there a secondary arch in that respect? I believe that in Mr. Kitty's construct, it's the knuckles which I suspect lend a springiness.

The apex of the arch is the part that goes from knuckles to wrist. So in that respect even the back of the hand belongs to the apex. If you observe your forearm while in the position I described you will see that both the forearm (its bottom) and the fingers with their round lines act as the sides of the arch white the straight zone on the top which is comprised of the wrist, hand and knuckles; act as a big keystone.

Now I'm curious to hear Mr. Kitty's arch - I have a feeling it's a microcosm to your macrocosm, and Kbk has some pulleys to add.

sorry for any misunderstanding.
It's a bit of a generalization but Russian pianists tend NOT to play with a pronounced knuckle arch.

The wrist is low, in a straight line from the elbow to the bridge og the knuckles running parallel to the floor.

Look at Disciple's video, or just about anything by Michelangeli and you'll see what I'm talking about.

Yes, I see what you mean. I'd say his wrist is not low so much as the forearm into hand make one straight line. (Michelangeli)
So is what you favour like what the Russian pianists do, or different, but you find strength in what they do anyway? I seem to remember that you have found something about a "square" which is sort of like a lifting of the fourth finger side - sorry, I have more of an image than words. And if so, does that go toward those pianists or unrelated?

The way I was taught to play is very different, almost opposite, to the way [most] Russians play.
Two performers with very "typical" Russian-style technique are Boris Berezovsky and Nikolai Demidenko.
Both are pianists on a titanic scale.
Very different approach to the physicality of playing the instrument than the one I adhere to.
Those two sit a bit higher, keep their wrists higher, and do not play with a pronounced knuckle arch.
I find a truly bizarre type of strength in the technique I was taught.

I still don't see this difference.
Kitty seems to play with the forearm parallel to the floor and wrist in a straight line with the hand and the forearm.

Knuckles?

pronounced arch:
http://youtube.com/watch?v=W8LoC3siqIY
http://youtube.com/watch?v=GmAQJYPAwAU&feature=related
http://youtube.com/watch?v=4wdJ5fj7REI
http://youtube.com/watch?v=kql_ztVUjOA

less arch:
http://youtube.com/watch?v=fb_dY864OJY
http://youtube.com/watch?v=G7y8zLnQi-M
http://youtube.com/watch?v=O5raMK4Z9co

It you look very closely, you'll see that Beresovsky has the arch going on there but it's much less pronounced than young Martha's in the Chopin Prelude.

When the arch is pronounced the palm has a flat, square shape to it. You can REALLY see it in the 2nd video when Chico Marx plays, particulary during his trills.

Yuma Osaki knuckles don't seem very pronounced and he hand, wrist and forearm look like your explanation of the "Russian" way.
The same for archerich.

It seems to me that shape the hand like an arch with pronounced knuckles one should have the wrist below knuckles level while all these examples had their wrist below knuckles level. The lower the wrist the more pronounced the knuckles and viceversa.