The shoulder complex is a multi-joint structure that provides the link between the thoracic cage and upper extremities. The shoulder complex has the highest degree of mobility of any joint in the body and as a result, the shoulder complex is very unstable. Because the bony structures of the shoulder complex provide relatively little support, much of the responsibility for stabilizing this region falls on the muscles, the ligaments, the joint capsules and proper shoulder mechanics.
We will now look a little deeper into the area of the shoulder complex by breaking it down into the following two regions:
THE GLENOHUMERAL JOINT-The glenohumeral joint is a ball-and-socket joint which is the area of articulation between the head of the humerus and the glenoid fossa of the scapula. The glenoid surface is one third to one fourth the size of the humeral head, this produces a minimum area of contact which in turn results in minimal stability. The joint must rely on static and dynamic stabilizers for its stability and its motion. The static stabilizers include the following but are not limited to the glenoid labrum and the glenohumeral ligaments (anterior, posterior, and inferior). The dynamic stabilizers include muscles that directly move the arm and they include the Pectoralis Major, Latissimus Dorsi, Teres Major, Coracobrachialis, the Deltoid consisting of the front, side and rear head and the rotator cuff consisting of the Supraspinatus, Infraspinatus, Subscapularis, and Teres minor. The glenohumeral joint has a large range of motion and great mobility that sacrifices stability.
THE SHOULDER GIRDLE-The shoulder girdle region contains the scapula and the clavicle and is made up of three joints the Acromioclavicular joint (AC joint), Sternoclavicular joint (SC joint), and Scapulothoracic joint which is not a true synovial joint. The Scapulothoracic joint is formed by the articulation of the scapula with the thoracic cage. Any movement of the scapulothoracic joint results in movement of the Acromioclavicular, Sternoclavicular, and Glenohumeral joints. The scapulothoracic joint provides mobility and stability for the orientation of the glenoid fossa and the humeral head for arm movements in all planes. The muscles involved in shoulder girdle movement, mobility and stability include the following but are not limited to the Pectoralis Minor, Serratus anterior, Levator Scapulae, Rhomboid Major and Minor and the Trapezius consisting of the upper, middle and lower fibers.
More Answers from Salvatore Lupia - NASM Elite Trainer