The subscapularis is a broad, flat muscle that lies between the scapula and the posterior rib cage. It covers the anterior surface of the scapula and lies superficial to the serratus anterior muscle.

The subscapularis is one of four muscles that make up the rotator cuff, a small group of muscles deep in the shoulder that surround the head of the humerus. The rotator cuff muscles all originate on the scapula and insert on the humeral head. Together, these small muscles stabilize the humeral head within the glenoid fossa of the scapula. Each muscle has a specific role in steering the head of the humerus within the shallow glenoid fossa as the arm moves into different positions. The subscapularis is the largest rotator cuff muscle and the only internal rotator of the four.

Primarily, the subscapularis stabilizes the humeral head during powerful downward movements of the shoulder and arm. It helps maintain the alignment of the glenohumeral joint as large prime mover muscles, such as pectoralis major, latissimus dorsi, teres major, and deltoid, rotate internally and extend the shoulder, pulling the raised arm downward. This is an essential movement for activities like throwing and hitting overhead, as in tennis or volleyball. In daily life, this movement helps close a vertical window or the hatch of a car. Executing overhead motions requires a precise balance between all four rotator cuff muscles. Each must have adequate strength and flexibility to maintain the position of the humeral head, centering it within the glenoid fossa.

Dysfunction of the subscapularis creates pain or weakness when performing shoulder extension and internal rotation from an overhead position. Clients may complain of pain or difficulty pulling their arm down forcefully. This may be the result of muscles impinging or becoming compressed against bony structures like the coracoid process of the scapula. Inflammation of the shoulder bursae or tendons of the rotator cuff may also result from weakness and/or lack of mobility in the subscapularis muscle.

A shortened subscapularis will often result in a slightly protracted scapular posture. The humerus also appears internally rotated during standing posture or when the client is lying supine. The muscle belly of subscapularis may become adhered to the underlying serratus anterior muscle, holding the entire scapula snug up against the posterior rib cage; this can limit scapular mobility globally, creating tension and pain in the posterior neck and shoulders. It is important to address mobility of both the subscapularis and the serratus anterior muscles in this instance.

Palpating Subscapularis

Positioning (see image below): client prone with arm slightly flexed and resting on practitioner’s leg

1. Palpate the lateral border of the scapula with the palmar side of the four fingers.

2. Press posteriorly and medially to the latissimus dorsi, which forms the posterior border of the axilla.

3. Use your other hand to scoop the scapula laterally, improving access to the anterior surface of the scapula, as you palpate the anterior surface.

4. Client resists shoulder internal rotation to ensure proper location.

Christy Cael is a nationally certified massage therapist, certified athletic trainer, and certified strength and conditioning specialist. Her private practice focuses on injury treatment, biomechanical analysis, craniosacral therapy, and massage for clients with neurological issues. She is the author of Functional Anatomy: Kinesiology and Palpation for Manual Therapists (Lippincott Williams & Wilkins, 2009), scheduled for release in October. Contact her at functionalbook@hotmail.com.

Subscapularis

Attachments

• Origin: subscapular fossa of the scapula

• Insertion: lesser tubercle of the humerus

Actions

• Rotates the shoulder internally

Innervation

• Upper and lower subscapular nerves

• C5–6

Client Homework—Stretching

Positioning: seated
or standing
1. Sit or stand straight with trunk aligned and head centered over your shoulders.

2. Reach straight up with the arm you will be stretching.

3. Let your elbow relax and bend while you grasp it with your other hand.

4. Gently pull your elbow toward the opposite shoulder until you feel a stretch in the back of your armpit.

5. Try actively pressing your scapula (shoulder blade) down toward the floor as you continue gently stretching the arm.

6. Take several deep breaths, relaxing into the stretch. Repeat as necessary.