Glossary of Directional Terms

Movement Terms

adduction – Movement towards the midline in the frontal place.

depression – Movement inferiorly.

elevation – Movement superiorly.

extension – Increasing the angle of a joint (straightening the joint).

flexion – Decreasing the angle of a joint.

hyperextension – Increasing the angle of a joint past 180 degrees.

lateral rotation – Rotation around an axis in the lateral direction.

medial rotation – Rotation around an axis in the medial direction.

protraction – Movement anteriorly in a horizontal plane.

retraction – Movement posteriorly in a horizontal plane.

Other Terms

action – The movement created when a muscle contracts (see movement terms above).

agonist – The muscle that is performing the action.

antagonist – The muscle that opposes the movement created by the agonist.

insertion – The moving end of the muscle.

origin – The stationary end of the muscle.

synergist – A muscle with an action not being performed but involved in making the movement more efficient. These muscles are usually paired muscles that are antagonists so that when both are contracted they stabilize the origin of the prime mover.