The antigravity shoulder muscles prepare to bring the arm to shelf level,and the hand is prepositioned and oriented to prepare forgrasp-ing.

• 当伸手动作展开时，前肋骨侧边的肌肉及上下颈部斜方肌会同时收缩使肩胛拉开向上，而旋转环膜会让肱骨呈外旋的姿势，并使得肱骨头置入关节窝。