Answer:
Vertical Plane.
Explanation:
Shoulder joint is at a right angle to the the rest of the body. It is a ball and socket joint capable of performing a constellation of movements which no other joint is caple of.
As the arm is at right angle to the body the rotational movement occurs in the sagittal plane normally if not coupled with other movements.When there is just rotational movement, the plane of the body and that of the movement are parallel.
