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When we think of the rotator cuff, the first thing that may come to mind is pain and quite often that may be the only thing that comes to mind. Yes, the rotator cuff can be a common source of pain and restriction. Although it is a pretty simple little group of muscles with each having a primary function and a secondary function, diagnosing, treating or fixing the issue can prove to be frustrating and time consuming. Although the only way to truly diagnose a rotator cuff injury is through imaging like and MRI, at least by understanding the anatomy of these 4 muscles we can begin to understand how we can have pain without experiencing a legitimate injury. We can also begin to seek out and correct movement and strength dysfunctions in the gym with a plan as opposed to randomly pushing on tender areas.
The rotator cuff is composed of 4 muscles. The infraspinatus, subscapularis, supraspinatus and teres minor. In simple view, each muscle has its own attachment points, its own primary job as well as a secondary job where it becomes a “helper” of another function. To begin to visualize these muscles, they are essentially grabbing ahold of the upper arm and attaching somewhere on the other side of the shoulder. It looks like they are pulling the arm into the shoulder socket, basically holding the arm to the torso.
Infraspinatus: This muscle is located on the backside of your scapula (shoulder blade) and attaches to the majority of the scapula including the edge closest to the spine. The other side attaches to notch on the humerus (upper arm) close to where the arm meets the shoulder joint. The main function of the infraspinatus is external rotation. With your arm straight to the side, twist your upper arm so that your thumb points outward. Secondarily, this muscle will assist in pulling the arm from a raised position back toward the body. As with all rotator cuff muscles, it also serves to stabilize the arm in the glenoid cavity (shoulder socket).
Subscapularis: This is typically the strongest muscle of the 4 and is also the largest. It attaches to the INSIDE of the scapula, (think between the shoulder blade and the rib cage) and it covers virtually the whole surface of the scapula as the other end of the muscle is attaching to its own bony bump on the frontside of the humerus. The main job of subscapularis is internal rotation, the exact opposite of infraspinatus. This muscle will aid in pulling the arm toward the body (adduction) and like all rotator cuff muscles, it also serves to stabilize the arm in the glenoid cavity.
Supraspinatus: This muscle is located on the back of the scapula, but at the very top. We have a large ridge located ¼ of the way down from the top of the scapula (spine of the scapula) and this muscle is located just north of that. This is often the landmark I use to help people find it. It attaches to the whole upper surface of the scapula while the other side attaches to its own bump toward the top of the humerus just above where the infraspinatus attaches. Its primary function is abduction of the shoulder joint (raising the arm away from the body) and can assist in internal and external rotation depending on arm position. As with all rotator cuff muscles, supraspinatus is contributing in stabilization of the glenohumeral joint (main shoulder joint).
Teres minor: This one is a little trickier to find due to its size and location and surrounding muscles. It is located on the backside of the scapula, on the bottom/outer border and just south of the infraspinatus and also attaches to the humerus just below where infraspinatus attaches. Its main job is externally rotating the shoulder along with infraspinatus. Teres minor will assist in raising the arm away from the body and plays more of a role in this function during the initiation of the movement (first 15 degrees or so). Like the other rotator cuff muscles, teres minor does play a role in stabilization of the humerus in the shoulder socket.
I hope this helps in visualizing the rotator cuff as a group and what its purpose is. The next post will begin to explore different common dysfunctions and injuries.