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I managed a 190 degree stretch once. Unfortunately, it hurts like hell(obviously, it is extremely taxing on the tendons and I've cheated to get that stretch, since it's practically inhuman from my observations) and doesn't help(except allowing some minimal expansion to my 180 degree stretch, as in I can stretch 180 degrees with my hands perfectly flat), since 190 degree length is the same as 170 degree, so it's pointless. So now, I'm stretching the joints(very dangerous, I know, but I do it with hands alone, as in stretching as far as a single hand will allow, no "assistance" from the other hand). I went from a somewhat comfortable minor tenth to an awkward major tenth that way.

I know, they demand that in level 9 RCM piano exams.

Ah yes. He was a very lucky man, unlike poor Robert. Of course, young Frycek was a boy at the time, unlike Robert who was a grown man when he attempted to do some...expansion. Plus, Chopin had been associated with flexibility(suppleness, as contemporaries of his said) of the hands and even body, I think, during his lifetime.

Over 180 is unnatural, really. XD 180 and you're good to go. It's not common for you to be playing with your hands stretched to its maximum anyway, because that eliminates the arch in your hand and really diminishes your power.

I did my finger stretching exercises as a child too, and it's probably much easier than doing it now. I have a friend who's left hand can stretch all the way, but her right hand looks cramped between her thumb and index finger--probably from bad playing position before, but her right hand can't really do octaves, unlike her left. She's trying to stretch it now, but it's proving very difficult now that she's fully grown.

I can reach 11ths, 10ths are comfortable, 9ths are my natural hand size when I put them in an open position on the piano xp (to me the most natural feel is a chord with two fifths, like C G D )

CRAP YO! an 11th??!! DANG. I can barely squeeze a 10th out! Dag yo. Man. If I could reach an 11th, dang I'd be SOO happy.