Dumbbell rows are undoubtedly one of the best mass builders for the back. It is also one of the most commonly improperly performed exercises. Most people never reap the full rewards of this exercise. The issue stems from an old wives tale that describes the exercise as somebody starting a lawnmower. This leads to a lot of torso rotation, as opposed to scapula retraction. This is what is supposed to be primarily rowing the dumbbell up. If you are twisting your body sideways to row it up, you are not hitting your lats at all. The key to this exercise is to use a weight that you can handle without using momentum to yank it in the air. During each rep, remember to not to over-rotate the body, otherwise you will not hit the targeted lats as much as you could be. Get a flat bench and put one knee on it. Then firmly plant the same side leg as the arm you will be using on the ground to keep your body stabilized. The opposite arm should be planted firmly on the front of the bench. Hold it there to stabilize the rest of your body and keep your back straight. To target your lats even more, row the weight further back towards your hips. To target your rear delts and traps more, row the weight straight up to the armpit area. You will add a lot of overall thickness to your lats and density to your back by doing this exercise correctly. I definitely attribute a lot of my back progression to the proper execution of this exercise.