Even though I got my ARCT 5 years ago and can stretch to reach a 10th, simply put, the torrent etude is the hardest etude I have come across played at the right speed, true presto, like how Richter did. At that speed, I have played all the other parts correctly but somehow the right hand in the start of the 2nd bar always gets me.
How can I practice that in a way that accounts for the physiology of the hand? Some people suggest playing it EXTREMELY slow, but it doesn't work as I tried that for 3 months already and there's no improvement. I then tried playing it at Richter's speed for that section for 2 months, and in each practice session there were a few tries hitting the correct sequence of notes, but it isn't consistent, no clear improvement until I tapered from doing that for 1 month. I can then play the section with greater accuracy at high speeds for 3 days, but the next few days I couldn't do it. The tapering process is too slow.
Some people suggested tapping on the table, but clearly, tapping on the table with a book the same height as the note's pressed depth doesn't work both when lifting the fingers to tap and no lifting of the fingers. Also, I've tried all sorts of different positions for the section but sometimes they work and sometimes they don't, and it's not a problem with strength because I don't work out my forearms AND I found that power napping helps with playing it at high speeds in a controlled manner (power napping relaxes certain muscles and improves others); hence, it's a problem with muscle activations – but the muscle/joint movements are extremely subtle, simply practicing trilling doesn't work.
My question is, for people who know hand anatomy very well, how can I improve the torrent etude? Or is there a more general tactic like power napping to focus on muscle activation for that specific section? I mean, I really want to get this section right so I can carry on with other pieces, and at times I can play it at high speeds in a controlled and accurate way, but it isn't consistent.
Some more information: I notice when playing at the position of the "controlled accurate way" which is the slight bend of the second finger joint in anticipation of the next part and immediate bend of the fifth finger joint upon the fourth finger hitting, sometimes my middle finger doesn't activate after the fourth finger hitting, but it always activates when the fifth note doesn't get hit, so 2343 is accurate at high speeds, not 23435. Possibly it is the stretch that makes it hard for me compared to Richter's massive hands. Also, 3435 with both the second finger holding the note down and second finger pointing horizontally is accurate at high speeds (however, I did notice that my middle finger in this case moves a little laterally to press the second time, maybe it uses the interossei instead of the fdp? Maybe I should focus on practicing middle finger pressing down straight, so to activate the other muscle), but just not 23435 – it's the combination 23435 that hinders me, when broken down into specific parts such as 3435 and 2343 it works quite well. But somehow, I managed to pull the section off at Richter's speed 5 times in a row accurately and in a controlled way in the 3 days after taper, so it's doable, I think.