The shoulder, comprised of the scapula (shoulder blade), clavicle (collar bone), and humerus (upper arm bone), is a highly mobile joint capable of positioning the hand virtually anywhere in space.
The scapula and clavicle enable the movement of the entire shoulder joint up, down, backward, and forward:
Elevation is the pulling of the scapulae in a superior, upward direction. The common description of this is a “shrug” of the shoulders. The joint moves up.
Depression is the pulling of the scapulae in an inferior, downward direction. This can be described as a “hunch” and can be accomplished by lifting the chest and pulling the shoulders straight down.
Retraction pulls the shoulder joint to the rear and toward the vertebral column. We can also call this “adduction of the scapulae.” A layman description might be “squeezing the shoulder blades together” or “bowing the chest.”
Protraction is the pulling forward of the shoulder joint. It can also be called “abduction” as the movement pulls the scapula away from the vertebrae. A layman description might be “rolling” or “rounding your shoulders forward.”
The possible movements of the humerus as it sits in the shoulder joint are:
Abduction, defined as the lateral movement of the arm away from the body.
Adduction, defined as the movement of the arm toward or across the body.
One other movement type possible at the shoulder, circumduction, is a fusion of the others. The simplest example is performing arm circles of 360 degrees. The shoulder utilizes all its capabilities to execute such a movement.
Extension is defined as a rearward movement of the arm to a point behind the body. (This is a counterintuitive term, because if you tell virtually anyone to “extend” their arm, they will either move it forward or overhead. This is due to the common perception that the word refers to lengthening something to create more reach.)
Flexion is defined as the forward movement of the arm to a point in front of the body.
External rotation is the twisting of the humerus in place to create an outward arc of movement of the arm.
Internal rotation is the twisting of the humerus in place to create an inward arc of arm movement.
In the illustration here, inward and outward rotation are depicted with a bent elbow to demonstrate rotation at the shoulder. It can be accomplished with a straight arm as well, but given that the wrist joint is also capable of rotation, the bent elbow used here isolates the rotation to the humerus only.