Hey Readers! I am so glad you are here! The term "rotator cuff" is super common and used frequently in the mainstream lexicon as well as in health and medical fields. You probably know that rotator cuff is in the shoulder, but do you know what muscles make up the rotator cuff and what they do? In this month's blog post, I will go over what the rotator cuff is made up of and what it does.
The rotator cuff (RC) consists of four muscles (i.e. supraspinatus, infraspinatus, teres minor, and subscapularis) that basically attach somewhere on the shoulder blade (i.e. scapula - to read more about the scapula click here) and upper arm bone (i.e. humerus). While each of the RC muscles has a different role to play in shoulder and arm movement (namely, rotating the head of the humerus, or upper arm bone), they all play a primary role in establishing dynamic stabilization of the shoulder joint (known as the glenohumeral, GH, joint). Re: stabilization, the RC muscles are responsible for reinforcing the GH joint by stabilizing the head of the humerus in the glenoid cavity of the shoulder blade (i.e. a small depression on the shoulder blade).
There is a pretty loose fit between the head of the humerus and the glenoid cavity (or fossa), permitting an extensive range of motion at the GH joint, and ultimately enhancing the reach of the entire arm. Essentially, the anatomic design of the GH joint favors mobility at the expense of stability. The RC group helps to stabilize the GH joint's natural laxity and propensity for instability. While most muscles that cross the shoulder provide some level of stability to the GH joint, the RC group truly excels in this capacity. The anatomic arrangement of the RC group forms a protective "cuff" (hence the name "rotator cuff") around the shoulder joint, becoming rigid when activated by the nervous system upon shoulder movement. Even though the RC muscles are arranged and designed to provide stability to the GH, or shoulder, joint, they also help to move the GH joint. Let's talk about the functions of each RC muscle!
Supraspinatus
The supraspinatus (pronounced "sue-pruh-spin-ate-us") is one of the most used muscles of the entire shoulder complex. This chunky muscle is located on the top of the shoulder joint, lying just underneath (or deep to) the trapezius muscle. The supraspinatus assists the deltoid muscle in abduction of the GH joint (i.e. lifting the arm out to the side). You abduct your shoulder when doing dumbbell side raises in a workout or when reaching to the side to grab something off your kitchen counter or the car seat next to you. Studies have shown that the supraspinatus and the deltoid muscle both produce about an equal share of the total abduction torque of the GH joint, meaning that both the deltoid and supraspinatus are equally involved in lifting the arm out to the side. In fact, if the deltoid was paralyzed for whatever reason, the supraspinatus muscle is capable of fully abducting the GH joint. The supraspinatus also helps to prevent downward dislocation of the humerus, such as when carrying a heavy suitcase. The supraspinatus and its tendon bear a lot of stress during many common activities of daily living (ADLs). The high forces, generated over many years, can partially tear the suprspinatus' tendon. The supraspinatus is innervated by the subscapular nerve.
Subscapularis
The subscapularis (pronounced "sub-scap-you-lar-is) is located on the scapula's anterior (or front) surface, forming part of the posterior (or back) wall of the axilla (or armpit region). This RC muscle is the chief internal (or medial) rotator of the humerus (along with the pectoralis major, latissimus dorso, teres major, and anterior deltoid), basically turning the head of the humerus inward, towards the body. Another way to think of internal rotation of the shoulder is to imagine turning the tops of your forearms in towards the side of your torso. You internally rotate the GH joint when you reach your hand around to scratch your back or when clutching an object close to your chest. One activity that naturally requires a large internal rotation torque (or force) of the subscapularis is high-speed throwing. The subscapularis is innervated by the subscapular nerve.
Infraspinatus and Teres Minor
The infraspinatus (pronounced "in-fruh-spin-ate-us") and teres minor (pronounced "tear-eez minor") are discussed together because they both have the same functions. These two RC muscles are responsible for externally (or laterally) rotating the GH joint (along with the posterior deltoid muscle), which basically means rotating the head of the humerus away from the body. The horizontal lines-of-pull of the infraspinatus and teres minor are ideal for this action. Both the infraspinatus and teres minor are located on the posterior (or back) side of the shoulder blade, as shown in the image above (note: the teres minor is not pictured above; however, this smaller muscle essentially runs the same direction as the infraspinatus, below, or inferior, to it). You externally rotate your shoulder when starting a pull-cord lawnmower, when fanning a smoke-filled room with your arms, or during the cocking phase of pitching a baseball. The infraspinatus is innervated by the subscapular nerve, and the teres minor is innervated by the axillary nerve.
Summary
The RC consists of four muscles (supraspinatus, subscapularis, infraspintaus, and teres minor) that all work together to provide stability to the unstable glenohumeral (GH) joint (i.e. shoulder), but also each have individual functions in helping to create movement at the shoulder. The RC muscles essentially attach somewhere on the upper arm bone (i.e. humerus) to the shoulder blade (i.e. scapula). The supraspinatus is responsible for abducting the shoulder (lifting the arm out to the side). The subscapularis is responsible for internally rotating the shoulder, such as when you reach behind you to scratch your back. Both the infraspinatus and teres minor are responsible for externally rotating the shoulder, such as when you are getting ready to throw a baseball. The RC muscles have a tendency to become overused and injured (known as "Rotator Cuff Syndrome") because they are used practically all the time, whether for stability or movement. Understanding these muscles' function and location can potentially help you to move with more awareness and mindfulness. Plus, I truly believe knowledge is power, so now you know a little more about the anatomic, and physiologic, arrangement of your shoulder. Thanks so much for reading!
As always, the information presented in this blog post is derived from my own study of human movement, anatomy, and yoga. If you have questions about your rotator cuff muscles, please follow up with your physician, physical therapist, or personal trainer. If you are interested in private yoga and/or personal training sessions with me, Jackie, email me at info@lotusyogisbyjackie.com for more information about my services. Also, please subscribe to my website so you can receive my monthly newsletters (scroll to the bottom of the page where you can submit your email address). This will help keep you "in-the-know" about my latest blog releases and other helpful yoga and wellness information. Thanks for reading!
~Namaste, Jackie Allen, M.S., M.Ed., CCC-SLP, RYT-200, RCYT, NASM-CPT, NASM-CES, NASM-CNC
References:
Biel, A. (2014). Trail Guide to the Body: A hands-on guide to locating muscles, bones, and more. 5th Edition. Books of Discovery. Boulder, CO.
Marieb, E.N. (2004). Human Anatomy and Physiology. 6th Edition. Pearson. San Francisco, CA.
Neumann, D.A. (2017). Kinesiology of the Musculoskeletal Systems: Foundations for rehabilitation. 3rd Edition. Elsevier. St Louis, MO.
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