The latissimus dorsi is a large, flat muscle that spans the middle and lower back, reaching up to the pelvis and the lower ribs. A well-developed latissimus dorsi gives the back a wider appearance, making the waistline seem narrower in contrast.

Functionally, the latissimus dorsi has several key roles including:

• Shoulder Extension: This occurs during any pulling motion, where the arms are brought down and back from an elevated position.
• Shoulder Adduction: Moving the upper arm toward the body, as seen in pull-downs or rows.
• Internal Rotation of the Shoulder: Twisting the arm so that the elbow points outwards, away from the body.
• Lateral Flexion of the Spine: Bending the torso from side to side.

Additionally, the latissimus dorsi aids in hyperextension of the spine (arching the back) and anterior pelvic tilt (the motion of sticking the buttocks out by tilting the pelvis forward).

In summary, the latissimus dorsi is actively involved in any pulling motion as well as in the bending and twisting movements of the spine. It plays a crucial role in the overall functionality and aesthetics of the upper body.