I 'can't stand' standing when I play the keyboard. Even in my early 20's it put considerable strain on my back because I've always required at least one foot pedal (sustain). To maintain healthy posture without developing back strain requires (at least for me) keeping both feet squarely on the floor when standing. Because I use sustain frequently throughout a song and throughout an evening gig, I position my keyboard height somewhere in between standing and sitting position, allowing me to sit on and/or lean against the edge of a high stool, of which helps support my balance and maintain body alignment when playing the pedal(s). Without the stool, it's like having to support my body all night on one (left) foot.