Latissimus dorsi m.

The latissimus dorsi m. is the large, flat, dorsolateral muscle on the trunk. It lies posterior to the arm and is partly covered by the trapezius m. at the midline on the back. The latissimi dorsi mm. are commonly known as the "lats”.

The latissimus dorsi is responsible for extension, adduction, and medial rotation of the humerus. It is very important in returning the arm to the side when the arm is extended overhead (e.g., climbing, some swimming strokes). It also has a synergistic role in extension and lateral flexion of the lumbar spine and can influence the movement of the scapula, rotating it downward during a pull-up.