Final answer:
The humerus will move about two times as much as the scapula for full range of motion overhead.
Step-by-step explanation:
For full range of motion overhead, the humerus will move about two times as much as the scapula. During upper limb abduction, the scapula undergoes superior rotation, in which the glenoid cavity moves upward as the medial end of the scapular spine moves downward. This motion allows the arm to be lifted above shoulder height and contributes to the full range of motion overhead. Without superior rotation of the scapula, the greater tubercle of the humerus would hit the acromion of the scapula, preventing full abduction of the arm.