Science & nature · Evidence-backed
Rotator Cuff Muscles
The rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis) originate from or insert onto the scapula and are essential for shoulder stability and movement.
The rotator cuff is a group of four muscles and their tendons that stabilise the shoulder joint, enabling a wide range of arm movements while keeping the humeral head centred in the glenoid fossa.
Supraspinatus initiates arm abduction
The supraspinatus muscle, located on the upper part of the scapula, is primarily responsible for initiating the abduction of the arm, lifting it away from the body's side in the first 0–15 degrees before the deltoid takes over. This function is critical for overhead reaching and is frequently assessed in clinical tests of shoulder impingement. Source: Britannica human muscle system overview.
Infraspinatus enables external rotation
The infraspinatus, a thick triangular muscle covering the posterior scapula, is the primary external rotator of the shoulder. It allows the arm to rotate outward away from the body, a movement essential for activities such as throwing, reaching behind the back, and maintaining shoulder joint integrity during rotation. Source: Britannica human muscle system overview.
Teres minor assists external rotation and stabilisation
The teres minor, a small muscle on the lateral border of the scapula, works alongside the infraspinatus to produce external rotation of the humerus. It also contributes to the overall stability of the glenohumeral joint, helping to keep the humeral head centred during movement. Source: Britannica human muscle system overview.
Subscapularis enables internal rotation
The subscapularis is a large, powerful muscle situated on the anterior (front) surface of the scapula. It is the main internal rotator of the shoulder, allowing the arm to rotate inward toward the body, and it also assists in adduction and stabilisation during pushing movements. Source: Britannica human muscle system overview.
Rotator cuff tendons fuse with the glenohumeral capsule
The tendons of the four rotator cuff muscles blend with the capsule of the glenohumeral joint, forming a continuous sleeve that reinforces the joint capsule. This anatomical arrangement provides dynamic stability and helps resist superior migration of the humeral head during arm elevation. Source: Britannica human muscle system overview.
Supraspinatus is most commonly torn in shoulder impingement
The supraspinatus tendon is the most frequently injured structure in rotator cuff pathology, particularly in subacromial impingement syndrome where repetitive overhead activities compress the tendon between the humeral head and acromion. Degenerative tears often begin here. Source: Britannica human muscle system overview.
Rotator cuff muscles originate from the scapula
All four rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis) originate from or insert onto the scapula, with their tendons passing under the acromion to attach to the greater and lesser tubercles of the humerus. Source: Britannica human muscle system overview.
Rotator cuff dysfunction leads to loss of shoulder range of motion
When the rotator cuff muscles are weakened or torn, patients experience significant loss of shoulder range of motion, particularly in abduction and external rotation, making everyday tasks such as dressing or reaching overhead difficult. Source: Britannica human muscle system overview.
Supraspinatus performs the initial 'setting' movement of the arm
Electromyographic studies show that the supraspinatus fires first during arm elevation, acting as a 'setting' muscle that initiates humeral head centration before the larger deltoid muscle generates the bulk of the lifting force. Source: Britannica human muscle system overview.
Infraspinatus and teres minor form the posterior rotator cuff
The infraspinatus and teres minor muscles together form the posterior aspect of the rotator cuff, providing the primary external rotation force and contributing to the dynamic stabilisation of the shoulder joint during throwing and reaching movements. Source: Britannica human muscle system overview.
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