Which of the following is a prime mover for scapular retraction?

The rhomboid muscles are indeed prime movers for scapular retraction. Their primary function is to draw the scapulae (shoulder blades) together towards the spine, effectively retracting them. This retraction is important in various movements, especially when performing exercises that focus on strengthening the upper back or maintaining proper posture.

The rhomboids also assist in stabilizing the scapula during arm movements and contribute to the overall function of the shoulder girdle. This makes them a crucial component in activities that require shoulder extension or retraction, emphasizing their role in stabilizing the scapula against the thoracic wall.

While the trapezius is also involved in scapular retraction, it has a more complex role, functioning in various movements of the shoulder girdle, including elevation, rotation, and retraction. The serratus anterior primarily aids in scapular protraction and upward rotation, and the pectoralis major has a more significant role in shoulder flexion and adduction. Consequently, among the given options, the rhomboid muscles are specifically noted for their direct action in scapular retraction.