I can never get as much air into my belly when I'm under load as I can without, so I get a huge belly breath and brace it down before I unrack the bar... That entire first rep is all on the same breath. I will do this for anywhere between one to three reps, depending on how many I'm going for. If at that point I need to take in more air, I will get my air at the top of the rep. So let's say I take my breath, I unrack the bar, I get three reps, and I need more oxygen. At lockout, I will rebreathe (take a couple little breaths), re-brace, huge belly breath, rebrace and then drop in for reps... then I just continue this pattern for as long as needed. Never EVER breathe when the barbell is in motion.