This pair of actions occurs about a transverse axis through a joint. The movement at a joint which decreases the angle between two adjacent body segments is know as flexion. The opposite action is extension, where the angle between body segments is increased. These actions are possible about an axis arranged in an antero-posterior direction through a joint. A reference point must be identified on the lateral aspect of the distal bone.
Lateral rotation is the opposite action.
The reference point is moved posteriorly or laterally, away from the body midline. Medial rotation involves a torsion of the distal bone so that the reference point is moved anteriorly or medially toward the body midline. Circumduction A combination of the actions of flexion, abduction, extension and adduction, in that order, is known as circumduction . Actions of the Scapula Several of the special muscle actions occur in the movement of the scapula. The scapula is rather firmly connected to the clavicle via the acromioclavicular joint, hence these two bones move together as a single unit.