Collapse the wrist or not? Or keep it straight?
The only way to accomplish this without pedal is to shift fingers. Which is awkward.
Hm I see. You know, the problem with theory books on practical exercises, is it simply doesn't show you how to do something and how it should feel. No amount of reading about how to drive a car and how it should feel could prepare you to drive a car 100% first time... Cortot's comments and theories have often been questioned (most likely just as every other theory book on playing the piano goes) with some users even suggesting injury from his instructions. I have no doubt his instructions are sound and can no doubt prove a massive success for some, however...I wouldn't take the concepts explained in books even by the best pianists word for word, because nobody can truly explain how it should feel or be to you, except you. Take their ideas and experiment yourself (if a piano teacher is not available) and see what works. Often core ideas of a practical matter are similar, for example all Olympic sprinters run on 2 feet, all top level pianists play the piano with 2 hands and 10 fingers, but when we get down to the nitty gritty details, generally known as "technique" we see many pianists approach and act very differently.Despite her reviews, the camera angles for Valentinas performances are often very good for the etudes to give you some ideas. Looking at her performance you can see her wrists remain high and it looks to me here is a combination of her wrists fluttering with a downward motions of the forearm. Again it may not be exact for you, but you could at the very least then consider a straight or U shaped wrist probably wouldn't work.When I try and practice this motion, to get as fast as I can (not even at a piano) what I find is the hand is still the lead of the movement and that drives the forearm down at quick speed, I don't think it's coming from the elbow, but I imagine that the wrist is flicking down and almost being rebounded from the keys to counter weight and then back down again and that makes the forearm follow.I imagine it as a hammer hitting a spring. If the head of the hammer was at the bottom rather than the top, you'd have no weight on the downward force. Lastly we must think of the fingers, if you tried to hit them down on the keys dead straight, it would be, in my opinion the same as jumping from a great height without bending your knees! OUCH! What happens when we jump and bend our knees? Without thought we straighten again, it's not conscious, we just do it to get back to position. I think for octaves at this speed similar happens, as you come down I imagine your thumb and pinky give way for a split second and then spring back to shape providing you the "spring off" upward force you need without actively trying to do it.
Hm I see. You know, the problem with theory books on practical exercises, is it simply doesn't show you how to do something and how it should feel. No amount of reading about how to drive a car and how it should feel could prepare you to drive a car 100% first time... Cortot's comments and theories have often been questioned (most likely just as every other theory book on playing the piano goes) with some users even suggesting injury from his instructions. I have no doubt his instructions are sound and can no doubt prove a massive success for some, however...