What is the main action of the latissimus dorsi?

The latissimus dorsi is primarily responsible for shoulder extension and adduction. This large muscle spans the lower back and extends upwards to attach to the humerus in the upper arm. When the latissimus dorsi contracts, it pulls the arm down and back, facilitating movements like pulling or rowing actions. The shoulder extension refers to moving the arm backward, while shoulder adduction involves bringing the arm closer to the body. This muscle is essential in various activities that require upper body strength, including lifting and pulling movements.

Other choices refer to actions that fall outside the primary functions of the latissimus dorsi, such as scapula elevation and scapula depression, which are primarily accomplished by other muscles like the trapezius and serratus anterior, as well as shoulder flexion, which is mainly governed by muscles such as the deltoids and biceps. Thus, shoulder extension and adduction capture the main action of the latissimus dorsi effectively.