The rotator cuff (will reference as RC from here on out) is a group of 4 muscles and their associated tendons that span the shoulder joint, or more anatomically speaking, the glenohumeral joint.
These muscles are: the supraspinatus, infraspinatus, teres minor, and subscapularis.
The RC is extremely vital to dynamic shoulder joint stability, as they are the only muscles that directly span the glenohumeral joint. While our bigger muscles, like our deltoids, lats, and pectorals control gross movements around the shoulder, the RC acts to stabilize the glenohumeral joint during these movements.
Why is it so important?
The RC primarily exerts a compressive and downward shear force at the glenohumeral joint. The compressive force is vital to keep the head of the humerus centered within the glenoid fossa. The downward shear force is vital in preventing the head of the humerus from migrating upwards. The area between the humeral head and the coracoacromial arch of the scapula is known as the subacromial space.
This space is extremely tiny, between 9-10mm! In this small space lie some very important structures, including the supraspinatus tendon, biceps long head tendon, subacromial bursa, and superior labrum. Normally, this 10mm of subacromial space is maintained as we move our shoulder throughout its range of motion through the stabilizing actions of a strong and intact RC. However, as the RC fatigues from excessive use, weakness, or lack of endurance, the shoulder joint becomes progressively less stable and the subacrominal space decreases. This can cause any of the above structures to become impinged between the humeral head and the coracoacromial arch. This leads to inflammation, pain, and ultimately an injury if left untreated. Weakness of the RC is very commonly associated with a host of shoulder pathologies, such as shoulder impingement, rotator cuff tendinitis, sub-acromial bursitis, biceps tendonitis, and rotator cuff tears. Common symptoms for rotator cuff/impingement pain include shoulder pain in the front and back of the shoulder, pain with overhead activities, and pain when lifting your arm to shoulder height, with or without weakness.
A strong and competent RC provides the stability that the shoulder joint, with its extreme range of motion, demands. Even if you aren’t experiencing any symptoms, RC strengthening should definitely be incorporated into your workout regime. A recent 2015 systematic review published in Manual Therapy further supports the use of RC strengthening and stretching as an effective treatment for subacromial impingement. Any internal or external rotation exercises of the glenohumeral joint will target the RC and improve glenohumeral joint stability.