What is the primary action of the pectoralis major muscle?

The primary action of the pectoralis major muscle includes a combination of movements that are essential for shoulder function. Specifically, this muscle is primarily responsible for horizontally adducting, flexing, extending, and medially rotating the humerus.

In terms of horizontal adduction, the pectoralis major assists in bringing the arm across the body, which is crucial for movements such as hugging or reaching across the front of the body. Flexion of the humerus occurs when the arm is raised forward and upward, such as when lifting an object overhead. Additionally, the muscle plays a significant role in extension from a flexed position and medially rotating the humerus, which facilitates a variety of upper body movements.

This multifaceted capability makes the pectoralis major a key muscle in many compound movements involving the upper limb and is fundamental in activities such as pushing, lifting, and throwing. Understanding these actions emphasizes the importance of the pectoralis major in dynamic upper body mechanics.