I was thinking about how much activity playing the piano takes...both mental and physical.
And how draining it CAN be on both, one's mind and body
I think piano is 80% a mental activity, maybe even more. I also beleive that certain music can be more physically demanding than other music, but it is still mainly a mental activity: you are constructing the music in your head as you play it, you are sending messages from your brain for your fingers to move in a certain way, and at the same time you are listening and feeling emotions. I think the reason you feel so exhausted after playing a challenging piece is mostly due to mental exhaustion, and partly physical exhaustion.
It is certainly possible to create music, for example away from the instrument, which is solely a product of the mind. However, I have found when I do this that the results are inclined to be "unpianistic".
I love all these percentages people seem to pull out. "Playing the piano is 95% mental." Where do these numbers come from??
OMG! I totally agree, I have been composing for a while now, and I have always had a nack for improvisation, and that's how I compose almost completely. (Some etudes and deliberately detailed sections I will work out on paper many times because it is so complex it is very helpful to have a plan in front of you) I am very pleased with the results I get from this, and music that some of my friends have written completely away from their instrument sounds....well not too musical and not too well thought out. I think it's the trial and error, along with the experimental nature of improvisation that allows a composer to...well, experiment with their emotions.
Could you show us some of your compositions? ( midi files, pdf, images,mp3, anything)