Muscle Minute TUESDAY - Meet the Subscapularis

Diagram of pectoralis minor muscles in human skeleton.

The subscapularis is a powerful muscle, the only internal rotator of the rotator cuff. It plays a role in anterior stabilization of the humeral head. It also helps you hug people. Let’s take a deeper dive.

Origin	subscapular fossa (anterior scapula)
Insertion	lesser tuberosity (humerus)
Action	internal rotation of humerus, anterior stabilization humeral head
Innervation	upper and lower subscapular n. (C5, C6)
Antagonists	teres minor, infraspinatus

The Real World Subscapularis

Three tests for subscapularis:

Gerber lift-off test: Patient places hand behind back on lumbar spine and lifts hand off back, extending and internally rotating the shoulder. This has been shown to be the most accurate test for subscapularis.
Belly press test: Patient places hand on belly and pushes inward. A positive test is if the patient pushes with wrist flexion versus a neutral wrist.
Bear hug test: Palm is places on opposite shoulder. Patient is instructed to hold the hand in that position while the clinician attempts to pull the hand off the shoulder.

Pain or weakness with any of the above tests may indicate a subscapularis tendonitis or tear.

An intimate connection. The subscapularis has been shown to have attachments to the bicep long head tendon, which sits in the intertubercular groove just lateral to the lesser tuberosity. Trigger points or tightness of the subscapularis may cause the bicep tendon to migrate medially out of the groove. This may also produce pain in the anterior shoulder with resistance to elbow flexion and internal rotation.

Friends for life. One of the most important relationships to the subscapularis is to its functional synergist, the ipsilateral gluteus maximus. During functional rotation to the right, for example when throwing a ball, the subscapularis is eccentrically loaded in conjunction with the same side butt. Subscapularis injury or overload may occur if the gluteus maximus is not doing its job or if hip or thoracic spine are limited on the same side.

Partnered with the ipsilateral gluteus maximus, the subscapularis decelerates external rotation of the glenohumeral joint, making it the primary stabilizer against anterior dislocation of the shoulder.

Here’s a short list of why this matters:

Due to its attachment, subscapularis may be involved with bicep long head subluxation
Anterior stability of the shoulder is dependent on an intact subscapularis AND a strong ipsilateral gluteus maximus
Subscapularis may be torn in 30-50% of patients with rotator cuff pathology.
It is a key muscle used in hugging

Conventional thinking says: The subscapularis internally rotates the shoulder, so strengthen it with theraband internal rotation exercise

Real World Thinking asks: The subscapularis works in concert with the ipsilateral gluteus maximus. If it is torn, one must assess the ability of the ipsilateral hip to internally rotate and load the gluteus maximus. Small muscles like the subscapularis are usually compromised when bigger muscles don’t come to play. So a proper rehabilitation program for the subscapularis should include retraining of the ipsilateral functional rotation pattern which includes: subtalar joint eversion, knee flexion, hip flexion and internal rotation and thoracic rotation.

Because nobody has time to be in pain.

Until next time…