Right hand on mouse, left hand on home row... moving either hand to hit the pgdwn key requires an arm movement from the shoulder. Whereas space is already under

Right hand on mouse, left hand on home row... moving either hand to hit the pgdwn key requires an arm movement from the shoulder. Whereas space is already under my thumb, and if I'm not in a form field, has no other use anyway. Historically, space is also the hotkey for 'more'.