That is interesting about the hand application.
I had an experience a couple of years back that may be relevant.
I'm primarily a trombone player. One of the things I taught myself during a period overseas when practice time was quite limited was to be familiar with all key signatures. I did this by taking one key a week and working it every day note by note - two notes at a time for my entire range, then three, then four, etc. This built motor memory (I hate that term, it's really in your brain, but we know what I mean) separately for each key. This is good on trombone, because there is often a choice of position for a given note, and a scale in one key signature may use very different choices than in another. The trombone is an asymmetric instrument where some half steps are close and easy, others very hard. The advantage of this exercise was that no key signature became intimidating, and I could sightread music in longer phrases rather than note by note.
Then I injured my right shoulder. No problem, you can put a trombone together left handed just as easily.
Except, the scales were gone. Not from muscle memory, where I expected some impact, but from theoretical memory. I could no longer remember what notes were in a B major scale without stopping to think. Or in an Eb major scale that I've probably played many thousands of times.