I am currently working on 10,2 alongside 25,6.
Assuming you did experience some 'growing pains' (literally) as I am, how long before your hand was fully acclimated to this piece? I get some discomfort in the right side of my hand after about the 3rd time through this piece.
I initially used this as a 'read through' to warm up for work on 25,6, but after it started to fall better into place I decided to fully embrace it.
Good job. May I ask how long you worked on it and roughly how intensely?
Thx. In the early stages, what helped me was "ghosting" - i.e. playing the right hand but just touching the keys, not pressing them down at all. Then pressing them down ever so slightly with absolutely minimum motion and effort.
This piece easily causes pain but not for the reasons one might think. The mere usage of the outer fingers isn't the problem. I can play the upper voice on its own with relative ease. It's the chords that make it so nasty as they interrupt the arm movements that naturally support the upper voice. There is no easy solution to it. At least I haven't found one.
You can try just playing the lower parts of the chord (the thumb) and see how much easier it is when your 2nd finger is allowed to stay close to the 3rd. Some pianists (won't mention names) also perform it like that even.
You can practice the upper voice while holding both thumb and 2nd finger far away (so you stretch between 2nd and 3rd) while doing that. Another approach is to snap the 2nd finger up as soon as it's "plucked" the chord. The thumb can stay close to the key as it's independent.
It's relatively new actually. I'd only learned the notes of it some years ago and periodically practiced it a little. Since the summer about I started regularly practicing it but only alongside others. I focused my attention on it after the last etude (November or something) but got interrupted with real life. But really turned the heat up about 2 months ago. I was worried I'd hurt my hand. Always had to curb my ambition to go that extra mile. This piece punishes that.