I switch between standing and sitting whenever I start feeling tired from standing or sluggish from sitting.
I did not know this whole 'standing whilst studying' thing was a thing. So are you saying that some people will stand whilst they read their textbooks / notes? And they do it for health related purposes? Cool.
Quite a few people walk while reading books and studying. I had a classmate who used to walk back and forth in the classroom while reading to himself aloud and gesturing violently :-)