Subscapularis

The subscapularis is a broad, triangular, and deep muscle that covers the anterior surface of the scapula. It is the largest and strongest muscle of the rotator cuff and is anatomically positioned on the anterior aspect of the scapula, within the subscapular fossa. Together with the joint capsule and ligaments, it forms an important anterior stabilizing structure of the shoulder joint.

Origin

The origin of the muscle is complex and extensive.

• The medial two thirds of the subscapular fossa, covering almost the entire anterior surface of the scapula.

• Multiple tendinous septa within the fossa provide attachment for muscle bundles oriented in different directions.

• Additional muscle fibers arise from an aponeurosis covering the lateral third of the muscle.

The fibers have a fan-shaped orientation and converge laterally toward the humerus. As the tendon approaches its insertion, it glides over the subscapular bursa, which reduces friction between the muscle and the neck of the scapula.

Insertion

The subscapularis inserts via a strong tendon into the following structures.

• The lesser tubercle of the humerus on its anterior aspect.

• The anterior portion of the glenohumeral joint capsule.

The tendon may communicate with the joint capsule and is often continuous with the tendon of the teres major.

Innervation

The muscle is innervated by two separate nerves from the brachial plexus.

• The superior subscapular nerve (C5–C6).

• The inferior subscapular nerve (C5–C6).

Both nerves arise from the posterior cord of the brachial plexus. They supply the superior and inferior portions of the muscle, allowing functional subdivision and segmental activation during different movements.

Blood supply

The subscapularis has a rich vascular supply from three primary sources.

• The subscapular artery, a branch of the axillary artery, which serves as the main supply.

• Direct branches from the axillary artery.

• The suprascapular artery arising from the thyrocervical trunk of the subclavian artery.

Extensive anastomoses in the axilla and around the scapula provide redundancy and ensure adequate oxygen delivery across varying arm positions and in the presence of trauma.

Adjacent structures

The subscapularis forms a large portion of the posterior wall of the axilla and is closely related to the following structures.

Anteriorly, toward the thorax

• The serratus anterior covers the superolateral portion.

• The thoracic wall and ribs lie directly beneath the muscle.

• Loose connective tissue between the muscle and the thorax allows gliding and enables scapulothoracic motion.

Posteriorly, toward the joint capsule and rotator cuff

• The supraspinatus, infraspinatus, and teres minor lie posterosuperiorly.

• The tendon of the subscapularis blends directly with the joint capsule and forms part of the rotator cuff.

Medially and laterally

• The central portion of the muscle is crossed by neural and vascular structures of the brachial plexus and axillary region.

• The posterior cord.

• The axillary nerve.

• The axillary artery.

• The axillary vein.

Intermuscular spaces

The subscapularis forms the anterior wall of three axillary spaces.

• The quadrangular space, bordered by the teres minor, teres major, and humerus.

• The upper triangular space, bordered by the teres major, teres minor, and the long head of the triceps.

• The lower triangular space, bordered by the teres major, the long head of the triceps, and the humerus.

Function

The subscapularis is the only internal rotator within the rotator cuff and has several roles depending on arm position.

Primary functions

• Medial rotation of the humerus.

• Adduction of the arm, particularly from an abducted position.

• Extension when the arm is elevated.

Stabilization

• Plays a key role in concavity compression by pressing the humeral head into the glenoid and resisting dislocation.

• Prevents anterosuperior translation during activity of the deltoid, pectoralis major, biceps, and triceps.

• Stabilizes the glenohumeral joint during overhead activities such as throwing and lifting.

Coordination with the scapula

• Contributes to coordinated movement between the scapula and humerus during arm motion, known as scapulohumeral rhythm.

• Plays an important role in transferring force from the trunk to the upper extremity during functional movements.

Clinical relations

Impingement

• During overhead activities, the subscapularis tendon may become compressed between the lesser tubercle and the acromion.

• The risk of injury is increased in throwing athletes, swimmers, and manual workers.

Tendinopathy and rupture

• May occur in isolation or in combination with supraspinatus injury.

• Symptoms include pain during internal rotation, weakness, and loss of the ability to place the hand behind the back, commonly assessed with the Lift-off test.

Nerve compression

• Edema or hypertrophy may compress the brachial plexus or the axillary nerve, resulting in paresthesia or muscle weakness.

Clinical significance

Shoulder stability

• The subscapularis forms the anterior portion of the rotator cuff and resists anterior dislocation.

• It is particularly important in glenohumeral instability and post-traumatic instability.

Frozen shoulder

• In adhesive capsulitis, shortening of the subscapularis may exacerbate limitations in internal rotation.

• The muscle may also become painful and contribute to reduced shoulder mobility.

Postoperative assessment

• Following shoulder surgery, particularly arthroplasty and rotator cuff repair, the integrity of the subscapularis is always evaluated.

• Rupture or loss of function results in significant impairment of shoulder function.

https://www.youtube.com/watch?v=2PiMaQjHLI0

Common injuries and symptoms

• Tendinopathy or partial tearOften secondary to overuse or degenerative changes.Typically causes pain during internal rotation and weakness on specific clinical tests.Patients often report anterior shoulder pain and difficulty placing the hand behind the back.

• Full-thickness tearResults in marked loss of internal rotation strength and shoulder stability.Common in older individuals and in athletes exposed to repetitive loading.

• Trigger pointsLocated deep within the subscapular fossa.May cause referred pain to the posterior shoulder, down the dorsal aspect of the upper arm, and in some cases toward the wrist.

Examination

Palpation

• Difficult to access due to the deep location of the muscle and the overlying thoracic wall.

• Indirect palpationThe arm is abducted and slightly externally rotated.The therapist palpates toward the thoracic wall behind the latissimus dorsi and serratus anterior.This technique may be uncomfortable for the patient.

Clinical tests

Lift-Off Test (Gerber’s test)

• The patient places the hand on the lower back with the dorsum of the hand against the body.

• Instruction: “Lift the hand away from the back.”

• Positive test: inability to lift the hand, indicating subscapularis rupture or significant weakness.

Belly Press Test

• The patient presses the hand against the abdomen while keeping the elbow anterior.

• With weakness, the elbow drifts posteriorly as a compensatory strategy.

• More sensitive for the superior portion of the muscle.

Bear Hug Test

• The hand is placed on the opposite shoulder with the elbow pointing forward.

• The examiner applies resistance into external rotation.

• Positive test: inability to maintain the position or marked weakness, indicating subscapularis involvement.

Napoleon sign / Belly-off sign

• A variation of the belly press test.

• The test is positive if the patient compensates with shoulder extension and is unable to keep the elbow forward.

Exercises and activation of the subscapularis

Research, isolation exercises, EMG findings, and clinical application

The subscapularis is a deep and powerful internal rotator that is difficult to isolate completely. However, research and EMG studies have identified several effective exercises and clinical principles for activation and rehabilitation.

Research and EMG findings

Multiple EMG studies, including those by Gerber et al. and Pennock et al., demonstrate that subscapularis activity is highest during:

• The lift-off test, reaching approximately 70 percent of maximal voluntary contraction.

• Bear hug and belly press tasks, which activate both the superior and inferior portions of the muscle.

• Exercises performed with the shoulder in slight abduction combined with internal rotation, which provide high activation with relatively low joint load.

An important consideration is that the superior and inferior portions of the muscle have different activation profiles. The belly press predominantly activates the superior portion, whereas the lift-off preferentially recruits the inferior portion.

Effective isolation exercises

The following exercises have been shown to activate the subscapularis effectively.

• Isometric internal rotation against a wallThe arm is held at the side with the elbow flexed to 90 degrees.The patient presses inward against a wall or towel.This provides minimal joint load and high early activation during rehabilitation.

• Resistance band belly pressA resistance band is placed around the back, and the palm is pressed against the abdomen.This increases resistance and allows progressive strengthening.

• Prone resisted internal rotation in 90/90 positionThe patient lies prone with the shoulder abducted to 90 degrees and the elbow flexed to 90 degrees.The forearm is rotated downward toward the surface against resistance.

• Standing cable internal rotationA resistance band or cable is set at elbow height.The forearm is rotated inward with emphasis on controlled movement and proper alignment.

• Push-up plus with narrow hand placementActivates the subscapularis synergistically with the serratus anterior.Commonly used in the functional phase of rehabilitation.

Functional multi-joint exercises

Although the subscapularis is not fully isolated, it plays a substantial role in several complex exercises.

• Pull-ups and lat pulldowns with narrow gripInternal rotation occurs during the concentric phase.Requires good scapular control.The subscapularis contributes primarily as a stabilizer.

• Turkish get-up and overhead carriesThe subscapularis works dynamically to stabilize the humerus.These exercises are useful in sport-specific and rotational training contexts.

Summary – what works best at each stage

Phase	Goal	Exercises
Acute / early rehabilitation	Pain reduction and activation	Isometric internal rotation, belly press, scapular control
Strengthening phase	Selective strengthening	Prone internal rotation 90/90, standing internal rotation, resistance band exercises
Late rehabilitation / functional	Control and strength during movement	Push-up plus, Turkish get-up, cable exercises, rotational lifts
Sport / high load	Maximal activation and control	Pull-ups, overhead holds, complex rotational lifts

Sources

1. Cael, C. (2010). Functional Anatomy: Musculoskeletal Anatomy, Kinesiology, and Palpation for Manual Therapists. Philadelphia, PA: Wolters Kluwer Health/Lippincott Williams & Wilkins.

2. Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2014). Clinically Oriented Anatomy (7th ed.). Philadelphia, PA: Lippincott Williams & Wilkins.

3. Netter, F. (2019). Atlas of Human Anatomy (7th ed.). Philadelphia, PA: Saunders.

4. Palastanga, N., & Soames, R. (2012). Anatomy and Human Movement: Structure and Function (6th ed.). Edinburgh: Churchill Livingstone.

5. Standring, S. (2016). Gray’s Anatomy (41st ed.). Edinburgh: Elsevier Churchill Livingstone.