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You said my system was “mostly” good. No, for me it’s ALL good …essential in fact. People can/will ignore/disagree with all/some of it … fine. The proof of it for me is that I can now play discomfort-free to a high standard for as long as I want. Others may benefit similarly if they take the same route. Each of us has to work out what is optimum for us.
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Right - there is no universal truth here, rather 'variations on a theme'. I probably do much of what you say, and have been using the same basic approach for close to 40 years, including the 'floating thumb' from long before it was brought to wider public attention by Willis. I am certainly not dogmatic about my left hand but that comes from experience. Sometimes my thumb is vertical, sometimes diagonal and sometimes parallel with the neck. Sometimes I use a 1-2-4 Simandl-style fingering, sometimes 1-3-4 Bille-style and sometimes a 'cello-esque 1-2-3-4. Sometimes I shift and other times I pivot on the thumb. And all the time playing perfectly in tune. One thing I don't do is over-curl my fingers - for me every joint from elbow to digit contributes to getting the tip down in the right place and at the right angle, which spreads the load and makes for longer levers. Longer levers = greater mechanical advantage = lower input effort for the same output force.
But the breathing thing is a really good point - it not only helps with posture and relaxation, but also helps produce better music, IME.
