Part way through the last practice I realized all of a sudden it had become much much easier - I was playing faster and louder with less effort. I looked down and my little finger had adjusted itself (totally without asking permission) so it was no longer playing on the tip but down on the shaft.
So what do you think? It works, but seems like cheating.
Cavear emptor as always but...IMHO "heavy work" "banging" - might be figures of speech - but they are suggestive that you're using more effort than you need to.
I'm fairly sure that trying to get higher melody notes to play over the bass by using effort is why I injured my right arm. It's almost a subconscious thing that you play louder to get the same volume [I'm left handed too, which probably accounts for less control over the right hand as well]
A piano teacher showed me something - It was just an exercise to play notes with the little finger(s) by moving lowering your hand with your arm from above the key, but you lower the arm very slowly and brush / press the key so softly that the force used to lower the key actually pushes the playing finger(s) back. At the lowest point you feel like you're "inside" the keys and if you hold the note, you're holding it with not much more effort than the non playing fingers.
The result is, as best I can describe it, visually similar to Yundi li's playing. Someone described that on youtube as "the fingers are pressing down the keys, but everything else is relaxed" [but in fact the arm is playing through a loose wrist]
You should be able to get loud without much more effort at all than that. At the same time you can play from the key rather than the exaggerated lowering, but still keep the essence of the movement and the feeling you get in your arms and fingers when you do it.
I'm finding it's a case of taking that basic idea and then applying irrespective of the position my fingers need to be in to play - whether that's flatter or more curved. I see that as a bit of a red herring TBH, I can do the same relaxed movement with my hands held as loose fists or with the palms.
To apply it to playing took a bit more mental effort though. Obviously to play you'll move the fingers from position to position, so your fingers do move. You can't play every note by lowering from above as in the exercise, and I found it more tricky to switch from finger to finger whilst keeping the same 'no effort' feeling, especially with pieces I've played but once I did, things like playing, say, the scales in K545 were much, much easier.
With the tension gone some of the stuff about the arm being used to make gestures and shape phrases that others have talked about begin to make sense too.