in extension？啥意思？

The levator scapula originates from the transverse processes of C1–C4 vertebrae and inserts into the superior angle of the scapula. It is innervated by C3–C4 cervical nerves and the dorsal scapular nerve (C5). This muscle elevates the scapula and laterally flexes the head when in extension.

肩胛提肌起源于C1-C4椎骨的横突，插入肩胛骨上角。由C3-C4颈神经和肩胛背神经(C5)支配。该肌肉伸展时抬高肩胛骨、使头部侧屈。

in extension？伸展时？指肌肉收缩？

国内的资料这么说：单侧肩胛提肌:上提肩胛骨、下回旋肩胛骨(肩胛胸廓关节)，侧屈头和颈，向同侧旋转头和颈

双侧肩胛提肌:后伸头和颈