Because of its relationship to the humerus, your lats support your shoulders and aid in arm movement. The lat muscle is one of the biggest in the human body because it extends to the middle of your upper arm bone (humerus). When you raise your body up by using your arm, your lat muscles come into play.
 

Just below the outside and upper back areas is where the lats, or latissimus dorsi, begin. They extend from the lower back down the length of the torso. Despite being a single muscle, the lats can be specifically targeted in the outer, lower, and middle lats using a variety of lat exercises, grip positions, and body position changes.

This Android app will help you learn easy and effective exercises you may do during your free time.