What are the 4 muscles in the shoulder? A Complete Breakdown

September 22, 2025 •

3 min read

Accounting for the widest range of motion of any joint in the body, the shoulder's complexity relies heavily on a small, but critical, group of muscles. Understanding what are the 4 muscles in the shoulder is the key to maintaining joint stability and preventing common injuries that impact mobility and daily function.

Quick Summary

The four key muscles in the shoulder are the supraspinatus, infraspinatus, teres minor, and subscapularis, collectively known as the rotator cuff. They are essential for stabilizing the glenohumeral joint and facilitating a wide range of arm movements and rotation.

Key Points

The Rotator Cuff: The four main muscles forming the rotator cuff are the supraspinatus, infraspinatus, teres minor, and subscapularis.
SITS Mnemonic: Use the acronym SITS to easily remember the names of the four rotator cuff muscles.
Crucial Stabilizers: The rotator cuff is essential for stabilizing the glenohumeral (ball-and-socket) joint of the shoulder.
Deltoid vs. Rotator Cuff: The deltoid is a larger, powerful muscle for arm movement, while the rotator cuff focuses on deeper joint stability and rotation.
Preventing Injury: Strengthening these muscles, especially the rotator cuff, is vital for preventing common shoulder injuries and maintaining mobility.
Holistic Approach: Optimal shoulder health requires addressing not only the main muscles but also the surrounding supporting muscles and ligaments.

The Rotator Cuff: Your Shoulder's Core Stabilizers

When people refer to the "4 muscles in the shoulder," they typically mean the rotator cuff. This group of four muscles and their tendons surround the glenohumeral joint, or the ball-and-socket shoulder joint. Their main role is to keep the head of the humerus (upper arm bone) centered in the glenoid fossa (shoulder socket) during movement, providing both mobility and stability.

The "SITS" Muscles: A Closer Look

The four rotator cuff muscles can be remembered using the mnemonic SITS:

Supraspinatus: Originating above the scapula's spine, it helps with the initial lifting of the arm away from the body (abduction) and stabilizes the humeral head.
Infraspinatus: Located below the scapula's spine, this muscle is a key external rotator of the arm.
Teres Minor: Positioned below the infraspinatus, it also aids in external rotation and joint stabilization.
Subscapularis: The largest and strongest rotator cuff muscle, found on the front of the scapula, it is the main internal rotator of the shoulder.

The Role of the Deltoid and Other Shoulder Muscles

While the rotator cuff provides deep stability, other muscles contribute to the shoulder's strength and shape. The prominent deltoid muscle gives the shoulder its rounded appearance.

The Deltoid: The Shoulder's Prime Mover

The deltoid is a large, triangular muscle with three heads, each contributing to different movements:

Anterior Deltoid: Located at the front, assists with lifting the arm forward (flexion) and internal rotation.
Lateral (Middle) Deltoid: On the side, it's the main muscle for lifting the arm sideways between 15 and 90 degrees.
Posterior Deltoid: At the back, assists with moving the arm backward (extension) and external rotation.

Supporting Muscles

Other muscles like the trapezius, rhomboids, and pectoralis major also help move the scapula and contribute to shoulder stability.

Comparison of Key Shoulder Muscles


Muscle Group	Primary Function	Primary Movement(s)	Stabilizing Role
Rotator Cuff (SITS)	Joint Stabilization	Rotation (internal/external), Abduction	Crucial; keeps humeral head centered in socket
Deltoid	Prime Arm Mover	Abduction, Flexion, Extension	Secondary; assists with movement beyond 15 degrees of abduction
Trapezius	Scapular Movement	Elevation, Depression, Retraction	Assists with overall shoulder girdle stability

Why Strong Shoulder Muscles are Essential

The coordination of the rotator cuff, deltoid, and other muscles enables a wide range of motion. Strengthening these muscles is important for several reasons:

Injury Prevention: Strong muscles, especially the rotator cuff, can help prevent injuries like tears, impingement, and dislocations.
Improved Mobility: Balanced shoulder strength supports smooth and controlled movement.
Enhanced Performance: Strong shoulders are beneficial for athletes and those active in sports.
Better Posture: A strong shoulder girdle contributes to better posture and can reduce neck and back pain.

For more information on anatomy, visit the official website of the National Center for Biotechnology Information at ncbi.nlm.nih.gov/books/NBK534836/.

Exercises for Shoulder Health

Targeted exercises can help build strength and mobility. It's best to start with mobility exercises before strengthening. Examples include:

Wall Angels: Improves posture and strengthens rotator cuff and scapular muscles.
External Rotation with Resistance Band: Targets the infraspinatus and teres minor.
Lateral Raises: Isolates the middle deltoid.
Scapular Retractions: Focuses on the rhomboids and trapezius for shoulder blade stability.

Conclusion: The Importance of a Balanced Approach

Understanding what are the 4 muscles in the shoulder is key to understanding shoulder mechanics. The rotator cuff is vital for stability, while the deltoid and surrounding muscles provide power for movement. A balanced approach to strengthening and mobility for all these muscle groups helps protect this versatile joint, promoting health and function for the long term.

Frequently Asked Questions

The four muscles, known as the rotator cuff, work together to stabilize the humeral head (upper arm bone) within the glenoid fossa (shoulder socket) during arm movement, providing both stability and a wide range of motion.

Yes, the four muscles are the supraspinatus, infraspinatus, teres minor, and subscapularis. A helpful way to remember them is with the acronym SITS.

The deltoid is a larger, superficial muscle that works with the rotator cuff. While the rotator cuff provides deep stability, the deltoid is the prime mover for lifting the arm. They work together for smooth, controlled shoulder function.

Weakness or injury in a rotator cuff muscle can lead to instability, pain, and restricted movement. This can cause issues like impingement, tendonitis, or a torn rotator cuff, often requiring targeted rehabilitation.

Yes, exercises like external rotations with a resistance band, wall angels, and specific drills for the supraspinatus can help strengthen and stabilize the rotator cuff. Proper form is crucial to avoid injury.

SITS is a mnemonic used to remember the four rotator cuff muscles: Supraspinatus, Infraspinatus, Teres Minor, and Subscapularis. It's a convenient way for students and professionals to recall the names.

The shoulder is a ball-and-socket joint with a high degree of mobility but relatively low stability compared to other joints. This makes the surrounding muscles, like the rotator cuff, highly susceptible to strain, overuse, and tears, especially in overhead movements.