The latissimus dorsi (plural: latissimi dorsi), meaning 'broadest muscle of the back' (Latin latus meaning 'broad', latissimus meaning 'broadest' and dorsum meaning the back), is the larger, flat, dorso-lateral muscle on the trunk, posterior to the arm, and partly covered by the trapezius on its median dorsal region. The latissimus dorsi is responsible for extension, adduction, transverse extension also known as horizontal abduction, flexion from an extended position, and (medial) internal rotation of the shoulder joint. It also has a synergistic role in extension and lateral flexion of the lumbar spine. Due to bypassing the scapulothoracic joint and attaching directly to the spine, the actions the lat has on moving the arm can also influence the movement of the scapulae, such as their downward rotation during a pull up.-Wiki-
