To really blast the mid-back muscles, which are often weak and underdeveloped, grab a suspension trainer and try this:
The Triple Threat Mid-Back Blast
This is a giant set of three pulling variants, which train the mid-back muscle from the center out. Here's the breakdown:
We begin with Y pulls because it's the most difficult of the three movements, and the most difficult to perform correctly. Since it's the weakest of the three movements used in this protocol, we have figure competitor Deanna Avery standing with a high body angle. Deanna also keeps her arms open in the shape of a "Y" (or V) to better match the line of action of the low traps.
The second pulling movement is wide elbow rows, which we do to hit the mid-traps, rhomboids, and rear-delts. The elbows are kept at a 90-degree angle to minimize biceps recruitment, which could take work away from the mid-backs muscles. Since we're using larger muscles than before, we can lengthen the lever arm (to add load) by moving the feet in toward the anchor point of the suspension trainer about one foot.
The final movement, underhand grip rows, is the easiest and strongest to perform because you can bring your lats and biceps into the game. That's why we have you walk your feet in another foot or so closer to the anchor points, raising the load further by increasing the lever arm.