Muscles pull the bones in various directions: forward, backward, to the side, and back in to the body. Each of these movements at a joint has a particular name Joint movements are allowed by the shape of the bones at the joint, and how they fit together.
To understand joint movements, it is best to start with an understanding of the ANATOMICAL POSITION, a reference position where the person is STANDING, FEET SLIGHTLY APART, FACE FORWARD, and ARMS HANIGING LOOSELY AT THE SIDES, PALMS FORWARD.
In the ANATOMICAL POSITION, bony joints are STRAIGHT, EXTENDED, or in EXTENSION.
EXTENSION: When joints are fully straight or returning toward the anatomical position. (A person standing has all joints extended).
FLEXION: When a joint BENDS comfortably in the anteior/posterior direction, such as bending the elbow, or bending the knee. (A person in the FETAL position, totally curled up, has all joints FLEXED or in FLEXION)
ABDUCTION: When a joint moves a bone or body part laterally, away from the midline, such as moving the entire arm or leg laterally
ADDUCTION: When a joints moves a bone or body part toward the body, such as moving the arm or leg medially