Anatomical terms of motion are used to describe the actions of muscles. All body movement, which is caused by muscle contraction, is classified by the directions in which the affected structures are moved. In human anatomy, all descriptions of position and movement are based on the assumption that the body is in the anatomical position. All motions are considered to be a mixture of or a single contribution by the following types of movement. Most terms of a motion have clear opposites, and as such, are treated below in pairs.
General Motion of the Body
|Adjusting angle between two parts||
Flexion - The opposite of extension; a bending movement that decreases the angle between two parts. Bending the elbow joint, or performing a sit-up are examples of flexion. When sitting down, the knees are flexed. Flexion of the hip or shoulder moves the limb forward (towards the anterior side of the body).
Extension - The opposite of flexion; a straightening movement that increases the angle between two parts. In the top of a pushup position, the arms are fully extended. When standing up, the knees are extended. Extension of the hip or shoulder moves the limb backward (towards the posterior side of the body).
|Adjusting relation to midline of body||
Abduction - A motion that pulls a structure or part away from the midline of the body (or, in the case of fingers and toes, spreading the digits apart, away from the centerline of the hand or foot). Abduction of the wrist is called radial deviation. Raising the arms laterally, to the sides, is an example of abduction.
Adduction - A motion that pulls a structure or part towards the midline of the body, or towards the midline of a limb. Dropping the arms to the sides, or bringing the knees together, are examples of adduction. In the case of the fingers or toes, adduction is closing the digits together. Adduction of the wrist is called ulnar deviation.
|Rotating body parts||
Internal rotation (or medial rotation) of the shoulder or hip would point the toes or the flexed forearm inwards (towards the midline).
External rotation (or lateral rotation) is the opposite of internal rotation. It would turn the toes or the flexed forearm outwards (away from the midline).
Elevation - Movement in a superior direction.
Depression - Movement in an inferior direction, the opposite of elevation.
Special motions of the hands and feet
|surfaces of the hands and feet||The palm (adj palmar) of the hand corresponds to the sole (adj plantar) of the foot. The adjective volar, used mainly in orthopaedics, is synonymous with palmar and plantar.||The dorsum (back) of the hand corresponds to the dorsum (top) of the foot.|
|rotation of the forearm||Pronation - A rotation of the forearm that moves the palm from an anterior-facing position to a posterior-facing position, or palm facing down. This is not medial rotation as this must be performed when the arm is half flexed. (See also Pronator quadratus and Pronator teres muscle.)||Supination - The opposite of pronation, the rotation of the forearm so that the palm faces anteriorly, or palm facing up. The hand is supine (facing anteriorly) in the anatomical position. (See also Supinator muscle.)|
|flexion of the entire foot||Dorsiflexion - Flexion of the entire foot superiorly, as if taking one's foot off an automobile pedal.||Plantarflexion - Flexion of the entire foot inferiorly, as if pressing an automobile pedal. Occurs at ankle.|
|movement of the sole of the foot||Eversion - the movement of the sole of the foot away from the median plane.||Inversion - the movement of the sole towards the median plane (same as when an ankle is twisted).|
Other special motions
|anterior/posterior movement - general||Protrusion - The anterior movement of an object. This term is often applied to the jaw.||Retrusion - The opposite of protrusion, moving a part posteriorly.|
|anterior/posterior movement - shoulders||Protraction - Anterior movement of the arms at the shoulders.||Retraction - Posterior movement of the arms at the shoulders.|
|motion within body (such as in blood vessels or the digestive system)||anterograde motion is in the normal direction of flow. (For example, passage of food from the mouth to the stomach.)||retrograde motion means reversed flow. (For example, gastric reflux.)|
Some additional motions without clear opposites are as follows:
- Rotation - A motion that occurs when a part turns on its axis. The head rotates on the neck, as in shaking the head 'no'.
- Circumduction - The circular (or, more precisely, conical) movement of a body part, such as a ball-and-socket joint or the eye. It consists of a combination of flexion, extension, adduction, and abduction. "Windmilling" the arms or rotating the hand from the wrist are examples of circumductive movement.
- Opposition - A motion involving a grasping motion of the thumb and fingers.
- Reposition - To release an object by spreading the fingers and thumb.
- ExRx.net - Articulations, great site for demonstrating each term of motion.
- Hypermuscle: Muscles in Action at med.umich.edu