The latissimus dorsi is a powerful muscle that plays a crucial role in many upper body movements. It is often referred to as the "lat" muscle, and is one of the largest muscles in the body. It is a broad, triangular muscle that originates at the lower six thoracic vertebrae and the lumbar vertebrae, and inserts at the humerus bone of the upper arm.

The latissimus dorsi is involved in several key movements of the upper body, including adduction (pulling the arm down and back), medial (inward) rotation of the arm, and extension of the shoulder joint. This means that the muscle is heavily used in activities such as rowing, swimming, and rock climbing, where these movements are important. In daily life, the latissimus dorsi is used in activities such as reaching for objects, carrying heavy items, and doing pull-ups.