Coming back to say that I personally have found that I need even more rest between the two upper body workouts, so from now on, I plan to do back/biceps on day 1, legs on day 3, and chest/triceps on day 4 or 5 (with cardio and stretch workouts in between). Just another option. For me, that gives my sensitive shoulder more time to rest, and means I can hit the weights hard each time I do an upper body workout.