Q:  Is it best to work back and legs on different days since they hit a lot of the same muscles?

A:  Yes, and here’s why: A properly performed set of squats or deadlifts will both blast the glutes, erectors and hamstrings to a significant degree. In addition it takes a lot of thigh to rip a limit deadlift off the floor. For this reason it is best to hit legs and back at the opposite end of the workout week. Do you really want to be doing heavy squats on muscles not recovered from back training the previous day? That is a recipe for poor performance and is potentially dangerous.