The one arm dumbbell row is great for working the back muscles. The largest muscle in the back is scientifically known as the latissimus. 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 fridge or a car door, you are primarily using the lat muscles.

To begin, place one knee on a bench. Then use your hand (on the same side) to support your upper body. In the opposing, hand grab a dumbbell and let it hang straight down. Next, pull the dumbbell into the side of your abdomen. Be sure to keep your elbow close to your side as you pull the weight up. Slowly lower the dumbbell back to the starting position and repeat the movement. You should exhale as you pull the weight into your abdomen.