I sing in a symphony chorus and in about a month we're going to have to stand for the entire verdi requiem.. . I'm guessing about 1.75 hr. I always get something that feels like a back spasm that makes me feel I have a band of pain around my back and rib cage. There are probably some easy instructions for this sort of standing (not able to change position nor put a foot up on something).. . Can anyone help?