"- if i then let it go, and let my wrist go loose and floppy, and let my hand fall down and pointing to the ground, it feels wonderful. that tiredness i felt in my wrist dissappears, which feels so relieving.
but at the piano, i'm getting the former (tired wrist) feeling even as i place my hands on the keys; my wrist looks "still" but it still gets tired!"
Sure- there's nothing inherently relaxing about being still- either at a piano or away. However, you can learn how to be totally comfortable by getting a feel for the minimum effort needed in both states. Away from the piano, you can learn how to feel the least effort required to only just stop gravity collapsing the wrist. Then once playing the keys even this effort can be released too.
Away from the piano practise hanging your wrist limp. Then feel a movement that is done so lightly, it barely overcomes gravity. When you stop moving, you cannot release this. If you released it even a fraction, you would start falling. At the top, try to feel how even the slightest release of the minimal effort allows gravity to very slowly pull you back down. It's the same principle as in the chicken clucking exercise for the shoulders. By scarcely moving at all, you improve sensitivity- so you no longer hold the wrist in a fixed position with "spare" effort but balance it perfectly. This is keeps it totally movable.
"then my wrists will be in proper playing position (ie more or less horizontal to the keys), BUT that it will feel as good as the second scenario in the experiment (ie letting the wrist flop loosely)?"
yeah, exactly. The effort is closer to the hanging wrist. Imagine a chain hung from one end compared to one pulled fairly taut from each end. There's no internal stiffness in the latter. Relaxing only causes limp dangling when you're supported at just one end.
"i am wondering about some of the videos that seem more arm-weight affiliated, that i've seen; where they lift their hands up from the keyboard and their wrists flop down very loose. to me, that /looks/ like it relieves the muscles that keep your wrists horizontal from continually doing their work."
Yeah. It's extremely valuable to be able to do that. But my belief is that everyone (who is successful) does much the same when contacting keys. The only time my wrists were relaxed before was when they were dangling, without contact with the keys. Upon contact, they stiffened. This is the moment that everything depends on.
"- are you saying that it /does/ in fact let those keep-wrist-horizontal muscles let go for a little bit, when you lift your hands up and let your wrists loose, but
` a) it's not necessary to have so much muscular work to keep your wrists horizontal, in the first place; because your main idea takes care of that, and
` b) even if you do let your wrists go loose when you lift your hands up, they will likely stiffen again when your fingers go down on the keys again?"
yeah, that's it. Dealing with tensions in between notes is pretty much futile- unless it spills over into what you do WHILE depressing the notes. It's like the equivalent of training someone who is careless at handling a knife how to apply plasters to wounds- rather than how to actually handle the knife. Relaxing after doesn't get to the real issues. People have assumed that any muscular activity is terrible and must instantly be turned off- which is why the "and then relax" is so popular. People who play with little feeling of effort generally just assume they must have just relaxed really quickly and that those who are stiff obviously need to relax faster after moving a key. But it's a collossal simplification to think that everything works harder to move the key and that everything is free to relax after. To retain unwanted stiffness after the key is depressed would be bad. But if you need to relax after playing a key, what you really need most of all is to eradicate what you're relaxing from at its source.