Glossary of Directional Terms
abduction – Movement away from the midline in the frontal place.
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 straight.
lateral rotation – Rotation around an axis in the lateral direction.
medial rotation – Rotation around an axis in the medial direction.
protract – Movement anteriorly in a horizontal plane.
retract – Movement posteriorly in a horizontal plane.
action – The movement created when a muscle moves (see movement terms above).
agonist – The muscle that is performing the action.
antagonist – The muscle that opposes the movement crated 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 a pair of muscles that are antagonists that when contracted stabilize the origin of the prime mover.