Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative to the anatomical position of the joints. Anatomists use a unified set of terms to describe most of the movements, although other, more specialized terms are necessary for describing the uniqueness of the movements such as those of the hands, feet, and eyes.
In general, motion is classified according to the anatomical plane it occurs in. Flexion and extension are examples of angular motions, in which two axes of a joint are brought closer together or moved further apart. Rotational motion may occur at other joints, for example the shoulder, and are described as internal or external. Other terms, such as elevation and depression, describe movement above or below the horizontal plane. Many anatomical terms derive from Latin terms with the same meaning.
Motions are classified after the anatomical planes they occur in, although movement is more often than not a combination of different motions occurring simultaneously in several planes. Motions can be split into categories relating to the nature of the joints involved:
Apart from this motions can also be divided into:
The prefix hyper- is sometimes added to describe movement beyond the normal limits, such as in hypermobility, hyperflexion or hyperextension. The range of motion describes the total range of motion that a joint is able to do.  For example, if a part of the body such as a joint is overstretched or "bent backwards" because of exaggerated extension motion, then it can be described as hyperextended. Hyperextension increases the stress on the ligaments of a joint, and is not always because of a voluntary movement. It may be a result of accidents, falls, or other causes of trauma. It may also be used in surgery, such as in temporarily dislocating joints for surgical procedures.  Or it may be used as a pain compliance method to force a person to take a certain action, such as allowing a police officer to take him into custody.
These are general terms that can be used to describe most movements the body makes. Most terms have a clear opposite, and so are treated in pairs.
Flexion describes a bending movement that decreases the angle between a segment and its proximal segment. For example, bending the elbow, or clenching a hand into a fist, are examples of flexion. When sitting down, the knees are flexed. When a joint can move forward and backward, such as the neck and trunk, flexion is movement in the anterior direction. When the chin is against the chest, the head is flexed, and the trunk is flexed when a person leans forward. Flexion of the shoulder or hip is movement of the arm or leg forward.
Extension is the opposite of flexion, describing a straightening movement that increases the angle between body parts. For example, when standing up, the knees are extended. When a joint can move forward and backward, such as the neck and trunk, extension is movement in the posterior direction. Extension of the hip or shoulder moves the arm or leg backward.
Abduction is the motion of a structure away from the midline while adduction refer to motion towards the center of the body. The centre of the body is defined as the midsagittal plane. These terms come from Latin words with similar meanings, ab- being the Latin prefix indicating "away," ad- indicating "toward," and ducere meaning "to draw or pull" (cf. English words "duct," "conduct," "induction").[b]
Abduction is a motion that pulls a structure or part away from the midline of the body. In the case of fingers and toes, it is spreading the digits apart, away from the centerline of the hand or foot. Abduction of the wrist is also called radial deviation. For example, raising the arms up, such as when tightrope-walking, is an example of abduction at the shoulder. When the legs are splayed at the hip, such as when doing a star jump or doing a split, the legs are abducted at the hip.
Adduction is a motion that pulls a structure or part toward the midline of the body, or towards the midline of a limb. In the case of fingers and toes, it is bringing the digits together, towards the centerline of the hand or foot. Adduction of the wrist is also called ulnar deviation. Dropping the arms to the sides, and bringing the knees together, are examples of adduction.
Ulnar deviation is the hand moving towards the ulnar styloid (or, towards the pinky/fifth digit). Radial deviation is the hand moving towards the radial styloid (or, towards the thumb/first digit).
The terms elevation and depression refer to movement above and below the horizontal. They derive from the Latin terms with similar meanings[c]
Rotation of body parts is referred to as internal or external, referring to rotation towards or away from the center of the body.
Internal rotation (or medial rotation) is rotation towards the axis of the body.
External rotation (or lateral rotation) is rotation away from the center of the body.
The swinging action made during a tennis serve is an example of circumduction
Dorsiflexion and plantar flexion refer to extension or flexion of the foot at the ankle. These terms refer to flexion in direction of the "back" of the foot, dorsum pedi, which is the upper surface of the foot when standing, and flexion in direction of the sole of the foot, plantar pedi. These terms are used to resolve confusion, as technically extension of the joint is dorsiflexion, which could be considered counter-intuitive as the motion reduces the angle between the foot and the leg.
Dorsiflexion is where the toes are brought closer to the shin. This decreases the angle between the dorsum of the foot and the leg. For example, when walking on the heels the ankle is described as being in dorsiflexion.
Plantar flexion or plantarflexion is the movement which decreases the angle between the sole of the foot and the back of the leg; for example, the movement when depressing a car pedal or standing on tiptoes.
A ballerina, demonstrating plantar flexion of the feet
Palmarflexion and dorsiflexion refer to movement of the flexion (palmarflexion) or extension (dorsiflexion) of the hand at the wrist. These terms refer to flexion between the hand and the body's dorsal surface, which in anatomical position is considered the back of the arm; and flexion between the hand and the body's palmar surface, which in anatomical position is considered the anterior side of the arm. The direction of terms are opposite to those in the foot because of embryological rotation of the limbs in opposite directions.
Pronation and supination refer most generally to assuming prone or supine positions, but often they are used in a specific sense referring to rotation of the forearm or foot so that in the standard anatomical position the palm or sole is facing anteriorly (supination) or posteriorly (pronation).
Pronation at the forearm is a rotational movement where the hand and upper arm are turned inwards. Pronation of the foot is turning of the sole outwards, so that weight is borne on the medial part of the foot.
Inversion and eversion refer to movements that tilt the sole of the foot away from (eversion) or towards (inversion) the midline of the body.
Eversion is the movement of the sole of the foot away from the median plane.Inversion is the movement of the sole towards the median plane. For example, inversion describes the motion when an ankle is twisted.
Unique terminology is also used to describe the eye. For example:
Other terms include: