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jennypenny focal dystonia, his condition, isn't caused by chairs...
https://en.m.wikipedia.org/wiki/Focal_dystoniaThe causes are unknown but the results are that mappings in the brain of what are normally distinct areas for each muscle group become indistinct. For highly trained fingers, this can happen in primates...
So it isn't a leap to link technique with this, bc overtraining seems to be implicated.
If you have seen pianists strain and sweat when they are doing little, that sort of strain is not consistent with ergonomic technique.