I have tried on several Fridays standing at work. I raise the desk so high that I can work standing, not sitting on the office chair.
I have a desk which can be raised or lowered by simply pressing a button, which is really convenient, even though the desk is not quite as stable in the high position as lowered down. But it works, "standing Fridays" seem to be a great idea.
I should start doing the same on other days as well, maybe half a day each work day, or something like that. One really notes the difference in how the muscles are used, and the first time I felt some strain after two or three hours, but today it wasn't so bad any more.
(Posting title is from the poem Mayakovsky by Frank O'Hara.)