What are the primary actions of the pectoralis major muscle?

The primary actions of the pectoralis major muscle indeed include adduction, horizontal adduction, and medial rotation of the humerus. This muscle is a key player in movements that bring the arms towards the body (adduction), move the arms across the chest (horizontal adduction), and rotate the upper arm inward (medial rotation).

When performing these actions, the pectoralis major assists in various functional tasks, such as pushing or throwing motions, which heavily rely on the muscle's strength and stability. In the context of upper body biomechanics, these movements are crucial for numerous activities, including weightlifting and many sports.

The other options involve actions that are either not primarily associated with the pectoralis major or pertain to different muscle groups or movements. Understanding the specific functions of the pectoralis major gives insight into how it contributes to overall shoulder mechanics and upper body strength.