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The scapula, commonly referred to as the shoulder blade, is the bone that sits above the rib cage in the upper back. The scapulohumeral muscles are muscles that connect the scapula to the humerus. The scapula can move in six directions, and each movement is produced by specific, primary muscles. The deltoid muscles cover and shape the shoulder, enabling arm abduction, flexion, extension, and medial and lateral rotation. The supraspinatus on the superior scapular region assists the deltoid in arm abduction. The infraspinatus on the posterior scapula causes lateral arm rotation. The teres minor causes extension and lateral arm rotation along with infraspinatus. The subscapularis, located at the anterior surface of the scapula, causes medial arm rotation.
| Characteristics | Values |
|---|---|
| Number of scapular muscles | 7 |
| Muscle that abducts the arm past 15 degrees | Deltoid |
| Muscle that assists the deltoid in arm abduction | Supraspinatus |
| Muscles that cause arm extension, adduction, and medial rotation | Teres major and latissimus dorsi |
| Muscles that cause extension and lateral arm rotation | Teres minor and infraspinatus |
| Muscle that causes medial arm rotation | Subscapularis |
| Muscle that helps with arm flexion and adduction | Coracobrachialis |
| Muscles that move the scapula | Middle trapezius, lower trapezius, rhomboid major, rhomboid minor, infraspinatus, teres minor |
| Muscle that influences the movements of the scapula | Trapezius |
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What You'll Learn
- Trapezius and serratus anterior muscles work together to abduct the scapula
- Teres major and latissimus dorsi cause arm extension, adduction, and internal rotation
- The deltoid abducts the arm past fifteen degrees
- The upper and lower trapezius and serratus anterior are muscle synergists for scapular upward rotation
- The infraspinatus, teres minor, subscapularis, and supraspinatus form the rotator cuff
Trapezius and serratus anterior muscles work together to abduct the scapula
The scapula, or shoulder blade, is a bone that sits above the rib cage in the upper back. It is involved in the creation of the shoulder joint, where it meets with the head of the humerus, or upper arm bone. The scapula can move in six directions, and each movement is produced by specific, primary muscles.
The trapezius and serratus anterior muscles work together to abduct the scapula. The trapezius muscle is located in the nuchal region and the dorsal part of the thorax. It originates from the external occipital protuberance, the nuchal ligament, and the spinous processes of the seventh cervical vertebra and of all the thoracic vertebrae. The serratus anterior is a fan-shaped muscle that originates on the superolateral surfaces of the first to eighth or ninth ribs at the lateral wall of the thorax. It inserts along the superior angle, medial border, and inferior angle of the scapula.
The coordinated interaction between the trapezius and serratus anterior muscles forms an essential force couple that enables efficient upward rotation and stabilization of the scapula during arm elevation. The upper trapezius initiates movement by elevating and stabilizing the scapula's superior angle. The serratus anterior becomes the primary upward rotator, pulling the inferior angle of the scapula laterally. The lower trapezius activates to counterbalance the serratus anterior’s upward pull by maintaining the scapula’s stability and pulling the scapular spine inferiorly.
The middle trapezius stabilizes the scapula in retraction, preventing excessive anterior tilt or winging. The lower trapezius and serratus anterior maintain scapular upward rotation to ensure the glenoid fossa stays aligned with the humeral head. The upward and lateral pull of the serratus anterior and the downward pull of the lower trapezius create a torque that rotates the scapula upward. The middle trapezius plays a stabilizing role, preventing lateral drift or winging.
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Teres major and latissimus dorsi cause arm extension, adduction, and internal rotation
The scapula, or shoulder blade, is the bone that sits above the rib cage in the upper back. It creates the shoulder joint where it meets with the head of the humerus, the upper arm bone. The scapula can move in six directions, and each movement is produced by specific, primary muscles. The trapezius and serratus anterior muscles work together to abduct the scapula.
The teres major is a small muscle that runs along the lateral border of the scapula. It is one of the seven scapulohumeral muscles that act around the glenohumeral joint to facilitate shoulder movement. The teres major assists in the extension and medial rotation of the humerus. It is sometimes called "lat's little helper" because of its synergistic action with the latissimus dorsi. The latissimus dorsi tendon inserts under the deltoid on the humerus, and the muscle originates from the lumbar vertebra and pelvis.
The teres major and latissimus dorsi muscles act in synergy to extend, adduct and internally rotate the shoulder. The latissimus dorsi is the prime mover of shoulder extension and adduction and may contribute to shoulder internal rotation (medial rotation). The teres major assists the latissimus dorsi in drawing the previously raised humerus downwards and backwards (extension, but not hyperextension). It also helps stabilise the humeral head in the glenoid cavity.
The teres major and latissimus dorsi muscles act in the acceleration and follow-through phases of the throwing motion in baseball pitching. Stretch or impact injuries to the teres major muscle, sustained while playing sports or in motor vehicle accidents, as well as falls onto the lateral scapula, are implicated in the evolution of teres major injuries. Isolated teres major injuries are rare but may occur in baseball or cricket players, especially pitchers and bowlers.
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The deltoid abducts the arm past fifteen degrees
The deltoid is a thick, triangular shoulder muscle that gets its name from its shape, which resembles the Greek letter delta (Δ). It is the principal abductor of the arm at the glenohumeral joint, but it can only abduct the arm when the arm is already lifted beyond 15 degrees. The deltoid cannot initiate abduction because it contracts parallel to the humeral axis. The initial part of abduction is produced by the supraspinatus muscle.
The deltoid is formed of three parts: the acromial (middle fibres), clavicular (anterior fibres), and scapular spinal (posterior fibres). The acromial part abducts the arm, while the clavicular and scapular spinal parts play a significant role in stabilization, ensuring a steady plane of abduction. The clavicular part can also act as a flexor and internal rotator of the arm, and the scapular spinal part can extend and externally rotate.
When the three parts of the deltoid contract simultaneously, the muscle can assist in abducting the arm past 15 degrees. Throughout abduction, the anterior and posterior parts of the deltoid stabilize the arm, while the lateral segment assists in raising the arm from 15 to 100 degrees. The deltoid also works with the rotator cuff muscles to stabilize the glenohumeral joint. When carrying heavy objects with the arm fully adducted, the deltoid produces a line of force (static contraction) that prevents the inferior displacement of the glenohumeral joint.
The deltoid is a very powerful muscle used in many activities of daily living, such as putting clothes on a line, carrying shopping bags, or washing hair. It is also used in athletic activities such as netball, swimming, and water polo. Deltoid pain can affect individuals who perform repetitive overhead activities, such as house painters, swimmers, and water polo players.
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The upper and lower trapezius and serratus anterior are muscle synergists for scapular upward rotation
The scapula, or shoulder blade, is a bone that sits above the rib cage in the upper back. It forms the shoulder joint where it meets the head of the humerus, the bone of the upper arm. The scapula can move in six directions, and each movement is produced by specific, primary muscles.
The serratus anterior is a fan-shaped muscle that originates on the superolateral surfaces of the first to eighth or ninth ribs at the lateral wall of the thorax and inserts along the superior angle, medial border, and inferior angle of the scapula. It is the prime mover in scapular protraction and scapular upward rotation. The serratus anterior becomes the primary upward rotator, pulling the inferior angle of the scapula laterally. The serratus anterior is also a key scapular stabiliser, keeping the shoulder blades against the ribcage when at rest and during movement.
The middle trapezius stabilizes the scapula in retraction, preventing excessive anterior tilt or winging. The upper trapezius maintains tension to support the scapula's position. The upward and lateral pull of the serratus anterior and the downward pull of the lower trapezius create a torque that rotates the scapula upward.
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The infraspinatus, teres minor, subscapularis, and supraspinatus form the rotator cuff
The scapula, or shoulder blade, is the bone that sits above the rib cage in the upper back. It forms the shoulder joint where it meets the head of the humerus, the bone of the upper arm. The scapula can move in six directions, and each movement is produced by specific muscles.
The subscapularis is the largest and strongest of the rotator cuff muscles. It completely covers the front of the shoulder blade and attaches to the front of the humerus, allowing the upper arm to move inward toward the centre of the body (internal rotation). The subscapularis also lets you hold your arm outstretched, away from your body. It attaches to the middle of your scapula and stretches to the lower part of your humeral head.
The infraspinatus helps you rotate your arm. It reaches from the bottom of the scapula and connects to the humerus behind the supraspinatus. The infraspinatus is a powerful lateral rotator of the humerus. The teres minor also helps with arm rotation. It attaches to the outside edge of the scapula and attaches to the humerus beneath the infraspinatus.
The supraspinatus muscle primarily helps bring the arm directly out to the side (abduction) and assists with other shoulder motions. It is the only muscle of the rotator cuff that is not a rotator of the humerus.
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Frequently asked questions
The trapezius and serratus anterior muscles work together to abduct the scapula.
The scapula, commonly referred to as the shoulder blade, is the bone that sits above the rib cage in the upper back.
There are seven scapular muscles that move the scapula. These include the teres major, latissimus dorsi, deltoid, supraspinatus, infraspinatus, teres minor, and subscapularis.
