The bent row with weighted straight bar primarily targets the greater muscles of the back. The largest muscle in the back is scientifically known as the latissimus dorsi. You might see it referred to as the "lats" or "wings." The lats are used any time you pull something (e.g. openning a fridge or car door).

Begin with your feet approximately shoulder width apart. With the weighted straight bar in hand, bend over about 45 degrees (Note: Your back does not have to be perfectly flat). The proper position is with the lower back arched and the butt out. Your neck should be neutrally aligned with your spine. Next, slowly pull the weighted straight bar into your abdomen. You should breathe out as you lift the weight. Finally, lower the weight back to the starting position and repeat the movement.