參考閱讀：
人體的方位、軸和斷面—圖解和視頻詳解，供學習和收藏
人體的方位、軸和斷面圖示
運動解剖學的常用術語，圖解便於學習、建議收藏
人體標準解剖學姿勢（醫學英語）
解剖平面（醫學英語）
解剖相對位置關係的術語名詞（醫學英語）
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視頻
Flexion and Extension
Flexion and extension are movements that take place within the sagittal plane and involve anterior or posterior movements of the body or limbs.
For the vertebral column, flexion (anterior flexion) is an anterior (forward) bending of the neck or body, while extension involves a posterior-directed motion, such as straightening from a flexed position or bending backward. Lateral flexion is the bending of the neck or body toward the right or left side. These movements of the vertebral column involve both the symphysis joint formed by each intervertebral disc, as well as the plane type of synovial joint formed between the inferior articular processes of one vertebra and the superior articular processes of the next lower vertebra.
In the limbs, flexion decreases the angle between the bones (bending of the joint), while extension increases the angle and straightens the joint.
For the upper limb, all anterior-going motions are flexion and all posterior-going motions are extension. These include anterior-posterior movements of the arm at the shoulder, the forearm at the elbow, the hand at the wrist, and the fingers at the metacarpophalangeal and interphalangeal joints.
For the thumb, extension moves the thumb away from the palm of the hand, within the same plane as the palm, while flexion brings the thumb back against the index finger or into the palm. These motions take place at the first carpometacarpal joint.
In the lower limb, bringing the thigh forward and upward is flexion at the hip joint, while any posterior-going motion of the thigh is extension. Note that extension of the thigh beyond the anatomical (standing) position is greatly limited by the ligaments that support the hip joint. Knee flexion is the bending of the knee to bring the foot toward the posterior thigh, and extension is the straightening of the knee.
Hyperextension is the abnormal or excessive extension of a joint beyond its normal range of motion, thus resulting in injury. Similarly, hyperflexion is excessive flexion at a joint. Hyperextension injuries are common at hinge joints such as the knee or elbow.
腕掌關節的屈曲和伸展
掌指關節的屈曲、伸展和過伸
拇指的伸展和屈曲
參考翻譯：
屈曲和伸展
屈曲和伸展是指在矢狀面發生的運動，涉及身體或四肢的前後運動。
對於脊柱，屈曲（前屈）是指頸部或身體的前（向前）彎，而伸展則涉及到向後運動，如從彎曲位置伸直或向後彎曲。側屈是指頸部或身體向右側或左側彎曲。脊柱的這些運動既包括每個椎間盤形成的聯合關節，也包括椎體的下關節突和下一個椎體的上關節突之間形成的平面滑膜關節。
在四肢中，屈曲意味著減少骨骼之間的角度（關節彎曲），而伸展則增加角度並拉直關節。
對於上肢，所有的前向運動都是屈曲的，所有的後向運動都是伸展。這些動作包括手臂在肩部的前後移動、前臂在肘部的前後移動、手在手腕的前後移動以及手指在掌指關節和指間關節的前後移動。
對於拇指，伸展將拇指從手掌移開，與手掌在同一平面內，而屈曲是將拇指帶回到食指或手掌中。這些運動發生在第一腕掌關節。
在下肢，使大腿向前和向上是髖關節的屈曲，而大腿的任何向後運動都是伸展。注意，大腿超出解剖（站立）位置的伸展受到支撐髖關節的韌帶的極大限制。膝關節屈曲是指膝關節的彎曲使足朝向大腿後部，而伸展是指膝關節的伸直。
過度伸展是指關節在正常運動範圍之外的異常或過度伸展，從而導致損傷。同樣，過度屈曲是指關節過度屈曲。過伸性損傷常見於鉸鏈關節，如膝關節或肘關節。
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重要詞彙：
flexion 屈曲
extension 伸展，伸
flexed 屈曲的
intervertebral disc 椎間盤
synovial joint 滑膜關節
articular processes 關節突
metacarpophalangeal 掌指的
interphalangeal 指間的
thumb 拇指
palm of the hand 手掌
carpometacarpal 腕掌的
thigh 股，大腿
hyperextension 過伸
hyperflexion 過屈
hinge joints 鉸鏈關節
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