How shoulders work
Understanding the shoulder
The shoulder is the most moveable and high functioning joint in the human body. It is not only affected by the movement and stability of one joint but instead is impacted by the movement of four joints and an exceptional amount of muscle stabilisation. With this in mind, understanding the dynamics of the shoulder is both interesting and worthwhile.
The main static stabiliser of the shoulder is the Inferior glenohumeral ligament. When the shoulder is positioned up and out to the side it is this ligament (via the front band preventing movement of the humerus forwards and by the back band preventing backwards movement of the humerus), which stabilises the joint.
The dynamic stabilisers of the shoulder are the rotator cuff muscles. This muscle group is comprised of the supraspinatus, infraspinatus, subscapularis, and teres minor muscles. These muscles work by co-contracting to counteract the force of the deltoid muscle in order to prevent the head of humerus moving upwards as the arm is raised. Any disruption to the tendons or muscle bellies of the rotator cuff may lead to pain and altered dynamics at the shoulder.
As I said earlier, the shoulder requires the adequate functioning of not only one, but four joints. These joints are: the glenohumeral, scapulothoracic, acromioclavicular, sternoclavicular joints, and the integrated movement of all of these joints is referred to as ‘scapulohumeral rhythm’.
Scapulohumeral rhythm should be smooth, co-ordinated and symmetrical and needs to be adequate to achieve full shoulder elevation. Abnormalities of scapulohumeral rhythm are usually due to weakness, shortening or poor control of the scapular stabiliser muscles (trapezius, serratus anterior, rhomboids, levator scapulae and pectoralis minor) and weakness or dysfunction of the rotator cuff muscles.
In conclusion, the shoulder relies on a vast number of joints, ligaments, capsules, and muscles to keep functioning adequately. For this reason it is important to exercise and train both your scapular stabiliser and rotator cuff muscles regularly in the appropriate scapular position which you can speak to any personal trainer or physiotherapist about.