In the pronated wide grip variant, the upper latissimus dorsi, the teres major, and the lower pectoralis major muscles are involved in shoulder joint adduction. In this action your arms are pulled down in a side (lateral) plane until your upper arm is below shoulder level. In the shoulder girdle, downward rotation of the scapulae is performed by the rhomboid and pectoralis minor muscles. In this action the right scapula rotates clockwise and the left counterclockwise (when viewed from the rear).
In the narrow neutral grip variant, the lower latissimus dorsi, the lower pectoralis major, and the teres major are involved in shoulder joint extension. In this action the arms move from in front of the body down to the sides of the trunk. This action is perpendicular to the lateral plane of movement as seen in the wide grip variant.
In the shoulder girdle the rhomboid, the pectoralis minor, and the middle trapezius are the major muscles involved in downward rotation and adduction of the scapulae. In this action the muscles pull the scapulae in toward the spine and at the same time rotate the right scapula clockwise and the left counterclockwise when viewed from the rear.