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. For example, when you open a refrigerator or a car door, you are primarily using your lat muscles. The one arm lat pulldown is a great way to work the back. The following are instructions for performing this exercise:

Ensure that the single handle attachment is connected to the cable pulley. If the machine has leg pads, adjust them as needed. Grasp the handle and sit down with one arm extended. Pull the handle down to your shoulder area. Be sure to keep an erect posture (chest high and back arched). Slowly allow the cable to ascend to the starting position. Be sure to control the speed of the weight going up. Stop the momentum of the weight just short of allowing the elbows to fully extend. Repeat the exercise on both arms.