What is the role of the pectoralis major muscle?

The pectoralis major muscle primarily functions in shoulder flexion and adduction, making the provided answer the most accurate. This muscle is a thick, fan-shaped muscle located in the upper chest, and it plays a critical role in various movements of the shoulder joint.

During shoulder flexion, the pectoralis major assists in lifting the arm forward, while its action in adduction helps bring the arm closer to the body. The muscle also aids in internal rotation of the shoulder. Additionally, the upper fibers contribute to flexing the humerus, while the lower fibers assist in bringing the arm down from a raised position.

Understanding this muscle's key functions can help in activities related to upper body movements, such as throwing, pushing, or lifting. It is critical for not just athletic performance but also for everyday activities that involve using the upper limbs.