Serratus anterior is misunderstood and overlooked by most manual therapists, despite its central function of stabilizing the scapula during all arm movements. In CTB we have come to recognize it as the hidden key to scapular positioning and hence, shoulder pain and movement dysfunction.
When a client has rounded shoulder posture (a.k.a. upper crossed syndrome) the shoulders are protracted and the scapular stabilizers do not have normal resting length/tension. Serratus anterior is a primary scapular stabilizer and tends to adaptively shorten and defacilitate. This, along with pec minor adaptively shortening results in the chronic protraction of the scapula. This misalignment of the shoulder will alter the scapulohumeral rhythm and then also impact the glenohumeral motion.
However, unlike pec minor, serratus anterior is a broad muscle that has many digitations and the muscle fiber directions can span more than 120 degrees! Some fibers protract/abduct the scapula. The low fibers upwardly rotate the scapula. The lowest fibers attaching to the 12th rib can be very vertical and capable of depressing the scapula. In addition, the highest fibers attaching to the first rib can produce scapular elevation. There are a lot of different motions possible by this one muscle!
The serratus anterior attaches to the ribs and to the medial border of the scapula. Because of its wide span of fiber directions, it is antagonistic to many other scapular stabilizers including: low trapezius, mid trapezius, high trapezius, rhomboids, and levator scapula. It is in length/tension relationships with all these muscles. That’s why most therapists fail to get a release of taut fibers in these other scapular stabilizers, particularly in the interscapular area. They are not addressing the antagonist, serratus anterior, the hidden key.
If serratus anterior is locked into protracting the scapula, the interscapular muscles (mid/low trap, rhomboids) lock into a lengthened position. The neuromuscular system “locks down” the muscles by purposefully creating taut bands (trigger points) in the muscles to provide stability without having to expend energy. Trigger points are metabolically stagnant. No ATP is then required to keep the static posture. The body basically creates a “fake ligament” with the trigger points. It is a strategy that makes sense and has been pointed out by renowned osteopath and author, Leon Chaitow. Many massage therapists and bodyworkers endlessly strip this interscapular area with as much gusto as they can muster (and their clients can handle), to no avail. Taut bands in the antagonist muscle, serratus anterior, must be released for these interscapular muscles to change.
Another important but overlooked issue with the serratus anterior concerns its referral pain. It projects referral along the lateral border of the scapula, down the posterior arm to the last 2 fingers, but most importantly right into the belly of the low trapezius near the inferior angle of the scapula. Low trapezius referral projects upwards into the mid trap, rhomboids and upper trap. So referral pain generated by the serratus anterior reaches all its antagonists via satellite referral! This is a phenomenon (an agonist referring pain over its antagonist) Chuck Duff has termed “reciprocal referral”. Muscle dysfunction in reciprocal referral situations can quickly spiral into severity, but can be addressed effectively if one understands this relationship. Referral pain originating in the serratus anterior can also cause posterior neck pain and even migraine headaches via satellite referral through the low trapezius.
As if all that wasn’t enough, the serratus anterior is also an accessory breathing muscle. Because of its rib attachments it is recruited to assist in expanding the rib cage on inhalation. Thus dysfunction in the serratus anterior can be caused by dysfunctional breathing. If a person doesn’t adequately use their diaphragm to breathe, the serratus anterior is recruited to do more work than which it was designed. This overload causes trigger points to develop and cascades into shoulder pain and dysfunction.
Serratus anterior has so many fiber directions and relationships; to antagonist scapular stabilizers, shoulder posture, reciprocal referral and breathing. Through many years of clinical experience, we have come to see it as the hidden key to shoulder pain and dysfunction. Some of the fibers are deep to other muscles and structures and inaccessible via palpation. Even these fibers can be influenced by the penetrating vibration of the Muscle Liberator making it the perfect tool to treat serratus anterior.