In which movement does the pectoralis major not participate?

The pectoralis major is primarily involved in movements such as medial rotation, adduction, and flexion of the shoulder. Each of these movements engages its various muscle fibers effectively.

In terms of extension of the shoulder, the pectoralis major is not a primary mover in this action, particularly when it refers to extension without assistance. The pectoralis major does have some contribution to shoulder extension when the arm is already flexed, but it is not its primary function, nor does it extend the shoulder from a neutral position effectively on its own. This is typically the role of other muscles, such as the latissimus dorsi and the teres major, which are more involved in shoulder extension when moving the arm from an anatomical position or a fully flexed position.

Thus, the correct answer is identified because the pectoralis major does not play a significant role in the extension of the shoulder when isolated from any assistance or additional forces.