The one-arm dumbbell row is a stretch-position exercise for the mid back. While it may appear that you get peak contraction at the top
of the range of motion, most trainees don't achieve complete contraction due to torso roll. As you pull up, your torso rolls away from
the dumbbell, which prevents peak contraction in your mid back.
Two-arm mid back movements performed with your arms slightly wider than shoulder width are best for hitting the midback's contracted position; for example, bent-arm bent-over laterals. This exercise allows you to squeeze your scapulae together at the top of the range of motion, which is a prerequisite for mid back contraction. Although your hands do come together at the bottom of bent-arm bent-over laterals, achieving the complete stretch position for the mid- back, because you're much weaker in the contracted position, you're forced to use a weight that you can take to the top, and that weight is going to be too light to force activation of the myotatic reflex. In addition, you should keep a constant bend at your elbows throughout the movement, which also prevents you from reaching the stretch position. So you now have one-arm dumb-bell rows for hitting the stretch position and bent-arm bent-over laterals for the contracted position.
As for mid back midrange movements, you should be pulling from overhead to hit this position, and your arms should travel slightly back to get some scapulae movement. Behind-the-neck pulldowns fit those specifications. With this exercise you get synergy from your biceps and lats, and if you concentrate on a scapulae squeeze at the bottom, you'll really feel every rep in your mid back.
The behind-the-neck pulldowns involve synergy from your biceps and lats and give your mid back a thorough heavy-weight hit. Then the one-arm dumbbell rows allow you to activate the myotatic reflex and prime your mid back for maximum fiber recruitment. The bent- arm bent-over laterals let you squeeze your mid back in the contracted position so you can fire the reserve muscle fibers that were called into action during the dumbbell rows. This is a very efficient and effective routine for building mid- back thickness.