You brought something to mind.... that comes up occasionally at our gigs. I'm a drummer.... I'm sitting the entire gig, right? So during a break what do I need to do?
Well, your guess is only partially right... I DO need to stand, stretch... briefly, very briefly... and then I need to sit. Makes no sense, right?
I don't even understand it... my guess is this: I'm not really sitting while playing... my butt is in contact with the seat, true, but only partially as I'm very much transferred to my feet for the bass drums and Hi-Hat. Also, I am NOT in a relaxed position... I don't lean back, for example.
Our bass player just a couple of years ago bought a 'bass chair'.. not sure that's what it's called, technically. It's like a stool but with a back and can swivel to switch upright position... from fully sitting to nearly standing. Leg position is always, and at any angle, nearly in a standing position, unlike a regular chair.
He swears by it... but i should note: He had very bad knees and had both replaced in the last few years.