Understanding how the human body moves requires a dual focus on two scientific disciplines: arthrology, the study of joint structure and function, and kinesiology, the study of musculoskeletal movement. While joints (articulations) are simply any points where two bones meet, the way they move—or don't move—is determined by their anatomical classification. In this article, we will explore the specific terminology used to describe body movements and examine the complex anatomy of key synovial joints, known as diarthroses.
Fundamental Movement Terminology
To describe movement accurately, anatomists use a "zero position," which refers to the body standing in the standard anatomical position. Movements are categorized by how they deviate from this position and the plane in which they occur.
Angular Movements
Most common at hinge joints, angular movements change the angle between articulating bones:
- Flexion: A movement that decreases the joint angle.
- Extension: A movement that straightens a joint, returning it to the zero position.
- Hyperextension: Extension that moves the joint beyond its zero position.
Frontal Plane Movements
These movements occur in the frontal plane (side-to-side relative to the midline):
- Abduction: Moving a body part away from the midline.
- Hyperabduction: Raising an arm over the back or front of the head.
- Adduction: Moving a body part back toward the midline.
- Hyperadduction: Crossing the fingers or ankles.
Vertical and Transverse Movements
- Elevation and Depression: Vertical movements in the frontal plane, such as shrugging the shoulders (elevation) or lowering them (depression).
- Protraction and Retraction: Movements in the transverse (horizontal) plane. Protraction is anterior movement (forward), while retraction is posterior movement (backward).
- Circumduction: A circular motion where one end of an appendage remains stationary while the other end moves in a circle.
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