[Chris]

I don't ever double my workouts (with the exception of the occasional cardio on weight day). IMO it's pointless. You'll be so far down the endurance scale that it's almost ineffective = waste of time. If you're concerned about the missed body part, do that instead of cardio on the next day and then resume schedule. I've often substituted the missed workout into my freeday. Or, I just say F'it and pick it up next time. Your muscles need occasional breaks anyway. No big deal.