Flexion
When referenced from anatomical position, flexion is decreasing
the angle of the joint, or movement out of
anatomical position.
(This motion is in the sagittal plane.)
Extension
When referenced from anatomical position, extension is increasing
the angle of the joint, or movement back to
anatomical position. Hyperextension is continuing
with extension past anatomical postion.
(These motions are also in the sagittal plane.)
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