The body’s connective tissue has structurally significant properties, enabling humans to function effectively throughout their everyday lives. Ligaments hold bones together. Tendons attach muscles to bones. Muscles act as motor units to move bones closer or further away from each other. Bones act as the internal framework that allows our body to move through various ranges of motion and also protect vital organs.
Three critically important joints that commonly endure musculoskeletal injuries include the lower back, knees, and shoulders. While the lower back and knees seem to get a little more attention, let’s not forget about the hypermobile, yet less structurally reinforced ball-and-socket joint of the shoulder. Raising one’s arm overhead requires a substantial amount of electrical signals sent from the brain, down the spinal cord, to the muscles attached to the shoulder joints, working in a harmonious symphony of neuromuscular interaction to execute a seemingly simple movement. Unlike its ball-and-socket cousin, the hip joint, the shoulder has a shallower socket, called the glenoid fossa, which grants an increased range of motion, but also increases the likelihood of injury if not properly strengthened and cared for. Appreciating the composition and functions that make joints move benefits everyday human functionality in more ways than appear on the surface level.
Similar to its cousin, the hip joint, the shoulder joint consists of the connection of a convex, nob-like attachment of the proximal portion of the humerus that inserts into a concave surface of the lateral border of the shoulder blade, much like blocks fitting into each other when playing a game of Tetris. The shoulder blade is also known as the scapula. This triangular-shaped bone is integral to the successful movement of the shoulder joint due to its high number of muscular, tendinous, and ligamentous attachment points. Muscles of scapular stabilization support optimal movements of the shoulder joint, enabling activities such as lifting objects overhead, reaching behind the body, or engaging in recreational athletic activities like golf, tennis, or pickleball. However, suboptimal conditioning of the muscles involved in scapular stabilization can lead to a range of debilitating conditions.
Throughout my college studies in exercise physiology and human anatomy classes, we used a mnemonic consisting of the letters “SITS” to aid in remembering four important muscles that originate from the scapula and attach to multiple areas of the humerus. Along with the other bones, tendons, ligaments, muscles, and an array of organs we had to memorize, remembering “SITS” was very helpful for young, easily distracted, and sleep-deprived students studying musculoskeletal anatomy during bi-weekly five-hour lab sessions. “SITS” refers to the muscles supraspinatus (S), infraspinatus (I), teres minor (T), and subscapularis (the other “S”).
Common shoulder functional insufficiencies caused by musculoskeletal problems typically result from disruptions to the connective tissue involving these SITS muscles. Possible symptoms of shoulder dysfunction include sharp, twingy, popping, or clicking pain when lifting the arm over the head or behind oneself. These symptoms can occur when performing regular everyday activities such as reaching through the holes of a shirt or jacket and assembling it over the top of the torso, reaching behind oneself to retrieve a seatbelt when driving, or throwing a ball during a recreational sporting activity, such as playing fetch with a dog or playing catch with a youngster.
The first “S” of the SITS muscles is the supraspinatus, which resides on the top portion of the shoulder blade, between the neck and humerus. The supraspinatus lifts the arm laterally away from the body, similar to a “snow angel” type motion. The “I” is the infraspinatus. It resides in the middle of the scapula and attaches to the back of the humerus. Its function is to assist in the “gate hinge” movement, such as rotating the humerus backward and abducting the arms posteriorly, similar to the opposite action of hugging someone. The “T” is the teres minor. It originates from the lateral border of the scapula and assists with external rotation and abduction. The second “S” is the subscapularis, which is unique due to its anterior origin and attachment points. One wouldn’t be able to see this muscle unless the scapula were removed from the body and someone could look underneath it. This commonly overlooked muscle is critically important for shoulder stability and mobility, particularly when internally rotating the shoulder and decelerating the shoulder as the arm is moved away from the torso. The subscapularis has robust attachment points on the anterior surface of the scapula and inserts in the middle of the ball-like prominence of the humerus. These muscles work in unison to hold the shoulder together and produce wide variations of upper extremity functionality.
Adhering to a strength and conditioning routine is crucial for maintaining shoulder strength, as well as the numerous physical, psychological, and emotional benefits it offers. Delving deeper into understanding the muscles that grant us human movement, such as the “SITS” muscles of scapular stabilization, can empower a happy, healthy, and strong life.
Sean McCawley, the founder and owner of Napa Tenacious Fitness in Napa, CA, welcomes questions and comments. Reach him at 707-287-2727, napatenacious@gmail.com, or visit the website napatenaciousfitness.com.