The glenohumeral joint is structured in such a way as to allow it to be the most mobile joint in the body.  With 120 of unassisted flexion and abduction of the arm over more than 90 (above the horizontal), the shoulder joint achieves a large range of movement required of the root of the upper limb in athletics and daily activities.  The full extent of the three-dimensional movement of the shoulder girdle and upper arm is achieved by the interaction of muscle strength on the underlying bones and the many diarthrosis and synarthroses joints of this girdle which are linked mechanically and act in unison. The fibrous joints greatly influence the control of the shoulder girdle joint. The range of motion of the sternoclavicular joint and the acromioclavicular joint is limited by ligaments. The costoclavicular ligament accomplishes and important stabilizing funtion because it connects truck and shoulder girdle (Wülker et al. 2001). In addition to the fibrous joints and shoulder joint, two slide bearings are significant for the kinematics of the shoulder: those being the subacromial space or ‘subacromial secondary joint’ and the scapulothoracic articulation (Wülker et al. 2001). Through these structures the bones of the shoulder girdle exhibit a wide range of motion: the scapula rotates upwards, tilts to the back and rotates externally (Ludewig  et al. 1996, McClure et al. 2001), the clavicle  elevates and retracts (McClure et a l.  2001,  Ludewig et al. 2004) and the humerus elevates and rotates externally (Ebaugh et al. 2006).  These movements however are never autonomous motions.Investigations into the kinematic and electromyographics of shoulder girdle movement have shown mechanically that every joint is linked and is involved in the initial phase of every elevation of the arm (Freedman and Munro 1966, Bateman 1978, basmajian 1980, Tillmann and Tichy 1986, Tillmann 1998).  For example, in the elevation of the shoulder in the frontal plane up to 150, 90 of the range of motion is allotted to the shoulder joint and 30 to each shoulder girdle joint. The glenohumeral joint  is either stabilised on (by fibrous joints) or moved into a certain position (by muscles) to generate, absorb and transfer forces that accomplish work or athletic tasks (De Vita et al. 2008).

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