The serratus anterior is a broad, fan-shaped muscle that wraps around the side of your ribcage, anchoring to the inner border of your shoulder blade. Its primary job is to hold the scapula flat against your back and rotate it upward when you raise your arm. When the serratus anterior works well, you barely notice it; when it fails, the shoulder blade juts out like a wing, and overhead movement becomes painful or impossible. Beyond its role in shoulder mechanics, this muscle turns up in surprising places: breathing physiology, chest-wall pain syndromes, regional anesthesia, reconstructive surgery, and even evolutionary biology.
Where It Sits and How It Is Built
The serratus anterior originates from the outer surfaces of the upper eight or nine ribs, near the side of the chest, and inserts along the entire length of the scapula’s medial border, the edge closest to your spine. The muscle is usually described in three functional parts. The upper portion attaches to the top ribs and the upper angle of the scapula. The middle portion fans out from roughly ribs two through four. The lower portion, which is the largest and most powerful section, arises from ribs five through eight or nine and converges on the scapula’s inferior angle, the bottom tip.
A cadaveric study dissecting 70 specimens confirmed this three-part arrangement and found that the nerve supply differs across sections. The upper part receives branches mainly from the C5 nerve root, sometimes with contributions from C4, C6, or C7. The middle and lower parts are supplied by the long thoracic nerve, which is formed from the C6 and C7 roots.1PubMed. A cadaveric study of the serratus anterior muscle and the long thoracic nerve A separate anatomical study showed that in the lower portion, the long thoracic nerve splits into many branches, and additional input arrives from intercostal nerves, giving that section a particularly rich nerve supply.2PubMed. An anatomic study of structure and innervation of the serratus anterior muscle This matters clinically: because different nerve roots supply different sections, an injury to one root can knock out part of the muscle while leaving the rest intact.
What the Serratus Anterior Actually Does
The serratus anterior’s signature action is scapular protraction, pulling the shoulder blade forward and around the ribcage. It also upwardly rotates and posteriorly tilts the scapula during overhead arm movement. Together these actions keep the socket of the shoulder joint pointing in the right direction as you lift your arm, which is essential for preventing the structures inside the shoulder from getting pinched.
The muscle does not work alone. It pairs with the trapezius in what clinicians call a “force couple,” a coordinated push-pull arrangement where the serratus anterior rotates the scapula from below while the trapezius does so from above. Observational data measuring these muscle force ratios in healthy people show that the lower fibers of the serratus anterior consistently produce more force than the lower trapezius or the rhomboids during normal shoulder use.3PubMed Central. Scapular force: Couple ratios in healthy shoulders – An observational study reflecting typical values When this balance tips, shoulder problems tend to follow.
Scapular Winging and Long Thoracic Nerve Injury
The most dramatic sign of serratus anterior failure is “winged scapula,” where the inner border of the shoulder blade lifts away from the ribcage. It is unmistakable when severe: push against a wall, and the blade pops out visibly. A consecutive series of 96 patients presenting with scapular winging found that 88% had a long thoracic nerve lesion. The leading cause was neuralgic amyotrophy, an inflammatory nerve condition, accounting for 47 of the 84 nerve-injury cases. Trauma was second, responsible for 33 cases.4PubMed. Scapular winging secondary to serratus anterior dysfunction: analysis of clinical presentations and etiology in a consecutive series of 96 patients
A separate electrodiagnostic study of 128 patients with unilateral winging offers a broader picture of the diagnostic landscape. Long thoracic nerve palsy accounted for 70 cases, spinal accessory nerve palsy for 39 (which affects the trapezius rather than the serratus anterior, producing a different winging pattern), and a handful of cases involved muscular dystrophy or orthopedic structural causes. Among the long thoracic nerve palsies, neuralgic amyotrophy was again the dominant trigger, present in 61 of 70 patients, and the right side was affected far more often than the left.5PubMed. Unilateral winged scapula: Clinical and electrodiagnostic experience with 128 cases, with special attention to long thoracic nerve palsy The right-side predominance may relate to hand dominance and the repetitive overhead or carrying motions that put the nerve at risk, though this remains debated.
How Clinicians Test for Serratus Anterior Weakness
The classic bedside test is the wall push-up test: you stand facing a wall, push against it with both hands, and the examiner watches whether the scapula wings. It is intuitive, but it has a problem. A study comparing the wall push-up test to a shoulder flexion resistance test found that the wall push-up was perfectly sensitive (it caught every case of lower serratus anterior deficiency) but had 0% specificity, meaning it could not distinguish serratus anterior weakness from other causes of abnormal scapular motion. The shoulder flexion resistance test, which applies manual resistance while the patient lifts the arm at different angles, achieved both 100% sensitivity and 100% specificity when tested across 30, 60, and 100 degrees of flexion.6PubMed Central. Serratus anterior dysfunction examination: wall push-up or shoulder flexion resistance test? In practical terms, the wall push-up is a good screening tool, but if it looks positive, a clinician should follow up with the resistance test to confirm the serratus anterior is truly the culprit.
Ultrasound imaging has also been explored as a way to measure serratus anterior thickness at rest and during contraction. Same-day reliability is generally good, but measurements taken on different days or by different examiners show more variability, which limits ultrasound’s usefulness as a standalone diagnostic tool at this stage.7PubMed. Ultrasound imaging of the serratus anterior muscle at rest and during contraction
The Link to Shoulder Impingement
Shoulder impingement, the painful pinching of tendons and bursa beneath the bony arch of the shoulder, is one of the most common reasons people see a doctor about shoulder pain. A review of muscle activity studies in people with impingement found a consistent pattern: decreased activation of the middle and lower serratus anterior, delayed firing of the middle and lower trapezius, and increased activation of the upper trapezius.8Brazilian Journal of Physical Therapy. Scapular and rotator cuff muscle activity during arm elevation: a review of normal function and alterations with shoulder impingement An electromyographic study comparing patients with subacromial impingement to healthy controls found significantly less serratus anterior activity in the symptomatic shoulders during both abduction and external rotation. Interestingly, altered muscle patterns also appeared on the non-symptomatic side, suggesting the abnormal motor strategy may be a contributing cause rather than just a consequence of pain.9PubMed. The activity pattern of shoulder muscles in subjects with and without subacromial impingement
The mechanism that connects serratus anterior weakness to impingement is straightforward. When the muscle fatigues, the scapula loses posterior tilt and drifts into internal rotation during arm elevation. A fatigue study confirmed that after the serratus anterior was experimentally fatigued, posterior tilt decreased between 60 and 120 degrees of arm elevation, and internal rotation increased, recreating the kinematic pattern associated with shoulder pain.10Journal of Sport Rehabilitation. Serratus Anterior Fatigue Reduces Scapular Posterior Tilt and External Rotation During Arm Elevation For anyone with recurrent shoulder pain during overhead activity, weak or poorly timed serratus anterior firing is one of the first things a physical therapist will investigate.
Best Exercises for Strengthening It
The serratus anterior responds best to exercises that combine scapular protraction with upward rotation on a stable surface. An early electromyographic study designed a progression of eight exercises and found that the push-up plus (a standard push-up with an extra rounding of the upper back at the top), the knee push-up plus, the dynamic hug, serratus anterior punch, and scaption with external rotation all reliably activated the muscle above 20% of its maximum contraction. The push-up plus and the dynamic hug produced the highest activity because they maintained an upwardly rotated scapula while accentuating protraction.11PubMed. Serratus anterior muscle activity during selected rehabilitation exercises
A systematic review and meta-analysis of 19 studies looking specifically at the push-up plus refined the picture further. The highest serratus anterior activity with the lowest unwanted upper trapezius activity occurred when the exercise was performed on a stable surface with arms fully extended, hands placed shoulder-width apart, and the shoulder flexed to around 110 to 120 degrees. Lifting the leg on the same side as the working arm also boosted serratus anterior recruitment. Performing the exercise on an unstable surface, by contrast, increased upper trapezius activity without helping the serratus anterior.12PubMed Central. Serratus Anterior and Upper Trapezius Electromyographic Analysis of the Push-Up Plus Exercise: A Systematic Review and Meta-Analysis A separate study in people with scapular dyskinesis confirmed this: an unstable surface decreased serratus anterior activity and increased trapezius activity, the opposite of what rehab aims to achieve.13PubMed. Electromyographic analysis of the serratus anterior and trapezius muscles during push-ups on stable and unstable bases in subjects with scapular dyskinesis
Among punch-style exercises, the serratus punch (lying on your back and punching a weight straight toward the ceiling) produced significantly more serratus anterior activity than pectoralis minor activity, making it a good isolation option. Modified push-up plus variations on a wall or the floor activated both muscles more equally.14PubMed. Serratus anterior or pectoralis minor: Which muscle has the upper hand during protraction exercises? Research also suggests that the pectoralis major stabilizes the activated serratus anterior during maximal protraction efforts, effectively boosting serratus anterior output, so the “serratus punch” posture may work partly because it allows this stabilization partnership.15PubMed. Effects of horizontal shoulder abduction and adduction on the activity and strength of the scapular protractors
The Serratus Anterior as an Accessory Breathing Muscle
Because it attaches to the ribs, the serratus anterior can help expand the ribcage during heavy breathing. An older but widely cited study detected phasic respiratory activity in the serratus anterior in every subject tested, with timing that was predominantly inspiratory. The muscle kicked in at lower breathing volumes when subjects sat leaning forward with elbows supported (about 35% of vital capacity) compared to standing relaxed (about 61% of vital capacity). The researchers concluded the serratus anterior should be classified as an accessory muscle of respiration, particularly in postures where its rib attachments are mechanically advantaged.16PubMed. Role of selected muscles of respiration as influenced by posture and tidal volume
A later study, however, tempered this conclusion. During upright cycling at increasing intensities in healthy subjects, the serratus anterior showed little muscular effort devoted to ventilation.17PubMed. Recruitment of the serratus anterior as an accessory muscle of ventilation during graded exercise The most likely reconciliation is that the serratus anterior can assist breathing, but in healthy, upright individuals it rarely needs to. It becomes more relevant in people with respiratory disease, those in leaning-forward postures (the “tripod” position familiar to anyone with severe asthma), or during extreme ventilatory demand.
Serratus Anterior Plane Block in Surgery
In the last decade, the serratus anterior has become a landmark for a regional anesthesia technique called the serratus anterior plane block. An anesthetic agent is injected between the serratus anterior and the surrounding tissues under ultrasound guidance, numbing the lateral branches of the intercostal nerves that supply sensation to the chest wall. A meta-analysis of randomized controlled trials found that patients who received this block after thoracic surgery had significantly lower pain scores at 2, 6, 12, and 24 hours, used less opioid medication, and experienced lower rates of postoperative nausea and vomiting compared to controls.18PubMed Central. The serratus anterior plane block for analgesia after thoracic surgery: A meta-analysis of randomized controlled trails
A narrative review of its use after video-assisted thoracoscopic surgeries notes that the block provides effective pain control of the anterolateral chest wall and carries a promising safety profile because the injection site is more superficial than alternatives like thoracic epidurals or paravertebral blocks.19PubMed Central. Serratus Anterior Plane Block for Pain Management After Video-Assisted Thoracoscopic Surgeries: A Narrative Review It has also been studied as an alternative to thoracic epidural analgesia for open thoracotomy and appeared to be a safe and effective option in that setting.20PubMed. Ultrasound-Guided Serratus Anterior Plane Block Versus Thoracic Epidural Analgesia for Thoracotomy Pain For patients where epidural placement is risky or contraindicated, the serratus anterior plane block has quickly become a go-to alternative.
Use in Reconstructive and Nerve Transfer Surgery
Surgeons also harvest the serratus anterior as a free flap for reconstructing defects elsewhere in the body. The muscle is thin, pliable, and served by a reliable blood supply from the thoracodorsal artery, making it useful for covering wounds where bulkier flaps would be impractical. A systematic review of lower-extremity defect reconstructions found data on 198 serratus-based flaps across 37 studies, with about 63% being serratus-only flaps and the remainder chimeric flaps that combined serratus tissue with other components from the same vascular pedicle.21Journal of Reconstructive Microsurgery. Reconstruction of Lower Extremity Defects Using the Serratus Anterior Free Flap: A Systematic Review and Retrospective Case Series In more complex cases, surgeons have used composite flaps incorporating rib, cartilage, muscle, and skin from the serratus anterior region to rebuild facial defects after cancer surgery.22PubMed. Free Composite Osteotomized Serratus Anterior Chondroosteomusculocutaneous Flap for Dynamic Reconstruction of a Pediatric Combined Maxillectomy and Hemimandibulectomy Defect
On the receiving end, when severe brachial plexus injuries leave the serratus anterior paralyzed, nerve transfer surgery can restore function. In a small series of five patients with C5-C6 root avulsions, the thoracodorsal nerve (which normally powers the latissimus dorsi) was rerouted to the long thoracic nerve. All five recovered serratus anterior function; two had complete resolution of scapular winging, and three had only mild residual winging. No significant loss of shoulder adduction strength was observed despite sacrificing the thoracodorsal nerve.23PubMed. Nerve transfer to serratus anterior muscle using the thoracodorsal nerve for winged scapula in C5 and C6 brachial plexus root avulsions
Myofascial Pain Originating from the Serratus Anterior
Trigger points in the serratus anterior can produce pain that mimics cardiac, pulmonary, or even abdominal conditions, making it a diagnostic headache for clinicians. The pain can radiate to the chest, back, neck, or arm, which is why serratus anterior myofascial pain syndrome is sometimes called a diagnostic conundrum.24Pain Medicine. Serratus Anterior Muscle Pain Syndrome: A Diagnostic Conundrum People with this condition often undergo extensive cardiac and pulmonary workups before anyone considers a muscular source. A key clinical clue is reproduction of the pain with direct pressure over the lateral ribcage and relief with targeted stretching or dry needling of the trigger points.
Congenital Absence and Poland Syndrome
In rare cases, the serratus anterior is absent from birth. Poland syndrome, a congenital condition defined by absence of the pectoralis major on one side, sometimes involves the serratus anterior as well. Imaging in such cases has revealed absence of the pectoralis major, pectoralis minor, latissimus dorsi, serratus anterior, and hypoplasia of the trapezius on the affected side.25European Respiratory Journal. Abnormalities of trapezius muscle may be a part of Polands syndrome Familial cases have also been documented outside of Poland syndrome. A three-generation family showed a pattern of absent shoulder girdle muscles: the grandfather lacked the lower two-thirds of the pectoralis major along with the serratus anterior and latissimus dorsi on one side, the father lacked the serratus anterior and part of the latissimus dorsi on one side, and the grandson lacked the sternocostal head of the pectoralis major on one side.26Journal of Medical Genetics. Familial absence of the pectoralis major, serratus anterior, and latissimus dorsi muscles This family’s pattern suggests that pectoralis absence is part of a broader spectrum of shoulder girdle developmental defects rather than an isolated anomaly.
An Evolutionary Perspective
The serratus anterior is not unique to humans, and its shape across primate species tells a story about how different animals use their forelimbs. In primates that rely heavily on climbing and hanging from branches, the lower fibers of the serratus anterior run more parallel to the trunk’s long axis. This alignment helps retract the scapula for propulsive climbing without dragging the entire shoulder girdle downward. In the human version, the muscle appears adapted for arm-raising functions, consistent with descent from a small ape with a broad chest.27American Journal of Physical Anthropology. An electromyographic study of serratus anterior in atelines and Alouatta: Implications for hominoid evolution
A recent comparative anatomy study across multiple primate groups found three morphological types of the serratus anterior and its neighboring muscles. The ancestral form appeared in all groups, while a derived type involving separation of the upper serratus anterior from the levator scapulae occurred only in great apes and humans, likely reflecting increased functional demands on the upper portion in species that use their arms overhead extensively.28PubMed Central. Comparative anatomy of the levator scapulae, serratus anterior and rhomboid muscles in primates In quadrupedal primates like vervet monkeys, the muscle (called serratus ventralis in that context) supports body weight during the stance phase of walking, but unlike in many non-primate mammals, it plays a relatively minor role in swinging the limb forward.29Journal of Zoology. Serratus ventralis function in vervet monkeys (Cercopithecus aethiops): are primate quadrupeds unique? Our version of this muscle, in other words, has been gradually repurposed over millions of years from a weight-bearing strut into a precision rotator that lets us reach, throw, and push overhead.