I really like bent-over barbell rows (BORs). BORs strengthen the muscles of the upper and mid back; unlike pull-ups, it is easy to vary the training load by adjusting the weight on the bar. The position the trainee assumes is extremely challenging which has benefits and drawbacks. Due to the difficulty of maintaining a strong position, it is often done incorrectly which places excessive strain on the lower back. Done correctly however, the lift trains the whole body which supports the weight in a strong position.
I recently completed a training cycle with a focus on BORs. In addition to the size and strength gains in my upper-back, which I expected, I also found I had dramatically increased my flexibility in hip flexion (bending forward). As it turns out, I had effectively incorporated a type of propioceptive neuromescular facilitation ("PNF") stretch into my training. By maintaining a strong lumbar position, I transmitted the dynamic load of the moving barbell to my hamstrings. Since the hamstrings maintained a long isometric hold by supporting the weight of the bell and my torso throughout the set, and had to react to a changing load as the barbell moved, I triggered both the inverse stretch reflex and myotatic stretch reflex, respectively. By triggering both reflexes, I adapted my nervous system to allow for increased flexibility.