The Shoulder Girdle, or Pectoral Girdle is formed by the clavicle (collar bone) and the scapular (shoulder blade). Together these act like a yoke, from which the arms are suspended on each side of the body.The shoulder girdle is part of the appendicular skeleton and only articulates with the torso, the axial skeleton, at the sternoclavicular joints which are formed on either side of the top of the sternum (breastbone). These joints allow the clavicle to move in response to arm and shoulder movements. This structure means that in effect, the arms and whole shoulder girdle, hang from these small joints made between the collar bone and breast bone.
The clavicle acts as a shock absorber and articulates with the scapular at the acromion. Unless it is pulled out of alignment, the collar bone acts as a strut, helping to push the scapular backwards and to widen the shoulders outwards.
The scapular, or shoulder blade, is only linked to our central skeleton, the axial skeleton, through the many muscles to which it is connected. It does not have a bony joint. This allows the scapular to move around the upper back and ribs fairly freely, unless restricted by muscle tension and mis-use.
The long bone of the upper arm, the humerus, articulates with the scapular at the gleno-humeral joint. This joint is shallow in order to allow the arms great mobility but it is also a somewhat insecure joint which can become dislocated.
The freedom of movement available to the arms is related to the integrity of the shoulder girdle and the manner in which it is used. When people tend to slump forwards a lot, so that the shoulders curl in and down, or perhaps do the opposite and rigorously 'pull the shoulders back' in order to 'sit up straight', the tension this often creates can restrict the range of arm movements available to them. Such restrictions can contribute to problems such as RSI.
Changes that can be seen in someone's body after they have had some Alexander Technique lessons, is that their upper back and chest often tend to be more open, they look more poised and the use of their arms tends to become much freer and easier.