My days off are not always the same, but I try to avoid training more than two days in a row. My work is usually the determining factor. This week was a bitch because I had to work additional days at two different labs, and I'm on call (and getting paged more than usual) all week long.
I had to miss a day, so I tweaked my schedule a bit to sacrifice back day, which is what I'll most often do when needed since my back is my best developed muscle group. I would hate to skimp on the others, which need much more attention.