The shoulder is a complex area of the body, comprising the glenohumeral joint (shoulder joint) which is formed by the head of the humerus and the glenoid socket of the scapula (shoulder blade). In order for it to move effectively, an extensive group of 'shoulder girdle' muscles work closely together to time the movement of both the scapula and the head of the humerus correctly and therefore produce 'normal' shoulder movement. The timing and co-ordination of this muscle firing is vital to ensure that movement patterns do not go wrong, however the balance frequently becomes upset, causing altered shoulder movement which leads to pain during activity and problems with function. The stability of the joint also relies upon the integrity of its ligaments, labrum (cartilage) and joint capsule in order to secure the ball in the socket whilst allowing normal movement to take place. In addition, as some of the shoulder girdle muscles are also involved in movements of the neck, both these areas must always be considered together when unravelling the source of a shoulder problem, and treatment may therefore target both areas in order to be fully effective.