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Understanding the Anatomy & Function of the Serratus Anterior

last updated December 15 0 comments

serratus anterior anatomy and function

Do you ever hunch your way through the day, feeling like your shoulders are permanently slumped? Or perhaps you've noticed a dull ache in your neck or a nagging pain between your shoulder blades? These common complaints might not just be annoying; they could be whispers from your hidden serratus anterior muscle yearning for your attention.

You may not realize it, but the serratus anterior muscle plays a pivotal role in your posture and upper body function. Often overlooked, this muscle is crucial for good posture and movement patterns. Let's explore the world of the serratus anterior and uncover its significance in maintaining a healthy posture and preventing injuries.

What is the Serratus Anterior Muscle?

Tucked beneath your ribs and attached to your shoulder blades lies a powerful muscle often overlooked: the serratus anterior. Nicknamed the "boxer's muscle" for its role in powerful punches, it is essential in shaping your upper extremity and trunk mechanics. While six-pack abs and biceps make the most noise on social media feeds – the fan-shaped serratus anterior is often overlooked for its role in optimal alignment and pain-free movement.

serratus anterior muscle

Anatomy of the Serratus Anterior

The serratus anterior, nestled around your rib cage, is the “armpit muscle” that attaches beneath your shoulder blades. This multi-purpose muscle spans from the upper nine ribs to the medial border of the scapula, playing a key role in moving and stabilizing your shoulder blades. Innervated by the long thoracic nerve, it is pivotal in your shoulder, upper limb, and thorax movements.

Actions:

  • Abduction of the Scapula: When you reach forward to fist bump a friend, the shoulder blade moves away from the spine and midline of the body (called abduction at the scapulothoracic joint).
  • Protraction of the Scapula: Picture reaching for a hug. This action pulls your shoulder blades forward, gliding over the rib cage (called protraction at the scapulothoracic joint).
  • Upward Rotation of the Scapula: Reaching for the cookie jar on the top shelf? Your serratus anterior assists as your arm moves upward, rotating your shoulder blade and maintaining scapular stability (at the scapulothoracic joint).
  • Depression of the Scapula: The inferior fibers of the serratus anterior muscle also assist in lowering the scapula on the rib cage (scapulothoracic joint).
  • Elevates the Thorax: When the shoulder blade is fixed, contraction of the serratus anterior muscle can lift the rib cage during forced inhalation.
  • Scapular Stability: The serratus anterior is a key scapular stabilizer critical to proper shoulder joint and upper extremity movement. In keeping the shoulder blades stable, the serratus anterior muscles prevent scapular winging, a common postural issue.

Attachments:

  • Origin: The serratus anterior originates from the first rib through the 9th rib, with "fingers" attaching to each individual rib. This broad base provides a powerful foundation for its actions.
  • Insertion: The muscle fibers converge at the medial border of the scapula, connecting to the shoulder blade in several places. This lengthy attachment allows for precise control over your shoulder blade movements.

Nerve Innervation:

  • The long thoracic nerve C5, C6, and C7, a branch of the brachial plexus spinal nerve roots, send signals to the muscle, coordinating its movements and ensuring smooth operation.

Blood Supply:

  • The serratus anterior receives a rich blood supply from several arteries, including the thoracodorsal artery, lateral thoracic artery, and superior thoracic artery.

The Integral Role of the Serratus Anterior in Posture and Movement

serratus anterior prevents scapular winging

A Keystone of Postural Integrity

The serratus anterior muscle is not only a contributor but a cornerstone in maintaining a strong and balanced posture. Due to its multiple attachments on the ribs and insertion on the full length of the medial border of the scapula, this muscle plays a pivotal role in the optimal positioning and movement of your shoulders, directly influencing your overall posture.

Defining Scapulohumeral Rhythm and Its Importance

Scapulohumeral rhythm refers to the coordinated movement between the scapula and the humerus (upper arm bone). This rhythm is essential for a full range of shoulder motion, allowing activities like reaching overhead to be smooth and pain-free. The serratus anterior is a key player in this coordination, ensuring that the scapula rotates and moves in harmony with the humerus. When the serratus anterior functions properly, it facilitates an efficient and balanced movement pattern required for everyday activities and athletic endeavors.

Impact on Rib Cage and Trunk

The serratus anterior also significantly influences the stability and movement of the rib cage and trunk. Anchoring the scapula firmly against the rib cage, it enables a more stable base for the arm to move, which is essential for the effective transfer of force and energy from the rotator cuff and throughout the upper body. This stable base is not just important for arm movements but also plays a role in the overall alignment and stability of the upper trunk.

For example, the serratus anterior and the external oblique muscles both play roles in the movement and stabilization of the trunk and upper body. The external oblique is one of the major abdominal muscles involved in rotating and flexing the trunk. Although these muscles have different primary functions, they work together for certain movements. When the serratus anterior protracts the scapula, the external oblique can assist in rotating the trunk, creating a coordinated movement for actions like throwing or reaching.

Consequences of Serratus Anterior Dysfunction

Several postural deviations can occur when the serratus anterior is weak or not functioning correctly. The most visible is the forward rounding of the shoulders, often accompanied by a protrusion of the shoulder blades, known as scapular winging. This misalignment disrupts the scapulohumeral rhythm, leading to compromised shoulder mechanics and potentially reduced range of motion or pain. Additionally, this dysfunction can lead to altered rib cage dynamics, affecting breathing and further exacerbating postural issues. (See more below)

A weakened serratus anterior affects the overall balance of the trunk, potentially leading to compensatory patterns in the lower back and neck. These compensations can create a cascade of musculoskeletal issues, including chronic pain, decreased mobility, and increased vulnerability to injury.


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The Serratus Anterior: A Team Player in Shoulder Movement

serratus anterior exercise

The serratus anterior, the muscle under the armpit and laced onto your ribs, is far from a solo act. This powerful muscle plays a crucial role in the complex orchestration of your shoulder and upper body movement, interacting with numerous other muscles to achieve harmony. Let's take a look into how the serratus anterior interacts functionally at the shoulder girdle:

1. Subscapularis and Rotator Cuff Muscles:

These muscles work closely with the serratus anterior to stabilize and internally rotate the shoulder joint. While the serratus anterior pulls the shoulder blades forward and upward, the subscapularis and rotator cuff muscles fine-tune the humerus position, ensuring smooth and pain-free movement.

2. Deltoid Muscle: 

The deltoid has three distinct heads and is responsible for various arm movements. The serratus anterior stabilizes and synergizes with the anterior, lateral, and posterior deltoid for arm flexion, abduction, and extension while preventing excessive winging of the scapula.

3. Trapezius Muscle:

 This large muscle group has multiple functions, and its interaction with the serratus anterior depends on the specific trapezius fibers involved. The upper trapezius works with the serratus anterior for upward scapular rotation and posture maintenance, while the middle and lower trapezius fibers act as antagonists, pulling the shoulder blades downward.

4. Pectoralis Major and Pectoralis Minor Muscles: 

These two chest muscles collaborate with the serratus anterior to protract the shoulder blades and bring your arms closer to your body. However, the pectoral muscles also contribute to internal rotation, amongst other movements on the chest wall, which the serratus anterior counterbalances for smooth shoulder movement.

5. Rhomboid Major Muscle and Rhomboid Minor:

 These muscles work alongside the serratus anterior to retract and downwardly rotate the shoulder blades, contributing to good posture and preventing winging. The serratus anterior calibrates this action, ensuring smooth and controlled scapular movement.

6. Latissimus Dorsi Muscle:

This powerful back muscle acts as both a synergist and antagonist to the serratus anterior. It assists in protraction and downward rotation of the shoulder blades, but it can also contribute to internal rotation, which the serratus anterior counteracts for optimal shoulder mechanics.

7. Levator Scapulae:

 This muscle elevates the shoulder blade, working in synergy with the serratus anterior for upward rotation during shrugging or overhead movements. However, the serratus anterior also helps control and stabilize the levator scapulae, preventing excessive upward movement of the shoulder blade.

By understanding these intricate interactions, you can appreciate the serratus anterior's vital role in coordinating movement and maintaining optimal posture. It's like a conductor, ensuring each muscle plays its part in perfect harmony, allowing you to move with grace and ease.


Identifying Issues Linked to the Serratus Anterior

When it comes to the health of your shoulders and upper back, the role of the serratus anterior is often central. Various symptoms and musculoskeletal conditions may arise from issues with this muscle. Understanding these can help you seek appropriate treatment and preventive measures.

serratus anterior injury
  1. Rotator Cuff Disorders: The serratus anterior plays a key role in stabilizing the scapula, which in turn affects the function of the rotator cuff. Weakness or imbalance in the serratus anterior can lead to abnormal scapular movement, placing undue stress on the rotator cuff muscles. This can manifest as pain during arm movement, weakness, and increased risk of rotator cuff tendinosis and tendinitis.
  2. Labral Issues: The shoulder's labrum, a fibrous ring of cartilage that surrounds the shoulder socket, can be affected by altered scapular mechanics due to serratus anterior dysfunction. This can lead to labral tears, causing deep shoulder pain and instability.
  3. Shoulder Joint Impingement: The serratus anterior helps guide the humerus (upper arm bone) in the shoulder joint. When it’s weak, the humerus can shift position, causing it to rub against surrounding tissues, leading to impingement and pain.
  4. Arthritis Development: Over time, abnormal movement and increased wear and tear on the shoulder joint can contribute to arthritis, leading to chronic pain and reduced mobility.
  5. Protracted Shoulder Blade (Winging): One of the hallmark signs of a weakened serratus anterior is the winging of the scapula, where the shoulder blade protrudes outwards abnormally. This affects the posture’s appearance as the inferior angle of the scapula juts out from the thoracic wall and can cause discomfort and limit the range of motion.
  6. Pain and Discomfort: Individuals may experience a spectrum of pain around the shoulder blade, ranging from a dull ache to sharp pains during specific movements. This discomfort is often exacerbated by activities that require lifting or overhead movements.
  7. Movement Limitations: Difficulty lifting objects, reaching overhead, or performing routine activities like brushing hair can indicate issues with the serratus anterior. These limitations often reflect a combination of pain, muscle weakness, and joint instability.
  8. Cervical Radiculopathy: The serratus anterior connects to the cervical spine through the body’s network of fascia. When the serratus is weak, it can pull on these structures, leading to nerve compression and pain radiating down the arm, a condition known as cervical radiculopathy.
  9. Altered Posture and Tension: Dysfunctional muscles can contribute to a forward-rounded posture and increased tension in the neck and upper back, leading to a cascading effect of postural imbalances and compensatory strain in other areas of the body.

Given its wide-ranging impact, issues with the serratus anterior require careful attention and targeted intervention. Recognizing these symptoms as potential signs of serratus anterior dysfunction is a critical step toward seeking appropriate care and restoring optimal function and comfort in your shoulder and upper back region.


Serratus Anterior Injuries: Causes and Prevention

Factors such as repetitive upper body movements, nerve injuries, or prolonged poor posture can lead to serratus anterior complications. Focusing on maintaining strong, flexible muscles through posture-corrective exercises is crucial to prevent those mentioned above.


The Holistic Approach of Posture Therapy: Whole-Body Function and Harmony

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Embracing the Whole-Body Perspective

Posture therapy transcends beyond merely focusing on the serratus anterior. It adopts a holistic approach, recognizing the interconnectedness of the body’s structures. This comprehensive method is pivotal in not only improving serratus anterior function but also in ensuring its seamless integration with the rest of the body.

Integrative Musculoskeletal System Strengthening

In posture therapy, exercises are designed not just to strengthen the serratus anterior but also to enhance the coordination and function of related joints, fascia, and muscle groups. This includes working on the rotator cuffpectoral muscles, and the muscles of the upper and lower back, creating a balanced muscular system that supports proper scapular movement and overall posture.

Promoting Optimal Postural Alignment:

The goal of posture therapy is to cultivate an alignment that supports the natural curves of the spine and balances the musculature. Improving the function of the serratus anterior within this context contributes to a more upright, relaxed posture, mitigating common issues like rounded shoulders and forward head posture.

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Frequently Asked Questions

What is the main action of the serratus anterior?

The primary action of the serratus anterior muscle is to facilitate the movement and stabilization of the scapula (shoulder blade). It plays a critical role in the protraction of the scapula, which means moving the shoulder blade forward and around the rib cage. This action is essential for activities that involve reaching or pushing.

Where is your serratus anterior?

The serratus anterior is located on each side of your upper rib cage, under your axilla (armpit). It stretches from the upper ribs to the medial border of the scapula (inner edge of the shoulder blade). This muscle is sometimes visible in well-developed athletes and is known colloquially as the "boxer's muscle" due to its prominence in boxers. They also look like costal gills on the rib cage or thoracic wall.

What is the function of the serratus anterior?

Beyond its role in scapular movement, it assists in the upward rotation of the scapula, which is crucial when raising the arm overhead. It also contributes to the stability of the shoulder joint and plays a part in the scapulohumeral rhythm, which is the coordinated movement of the scapula and humerus (upper arm bone).

Is the serratus anterior a chest muscle?

While the serratus anterior is not a chest muscle like the pectorals, it’s more of an armpit muscle located near the chest, along the side of the rib cage. It works closely with chest muscles, especially the pectoralis minor, in controlling scapular movement and position.

What does the serratus anterior muscle have to do with the brachial plexus?

The serratus anterior muscle is innervated by the long thoracic nerve, a branch of the brachial plexus, which is a network of nerves running from the spine through the neck, axilla (armpit), and into the arm. Dysfunction or injury to the serratus can sometimes lead to issues within the brachial plexus, affecting nerve function and potentially causing symptoms like pain, weakness, or numbness in the arm and shoulder region.

How does the serratus anterior affect clavicle movement?

While the serratus anterior primarily influences the movement of the scapula, it indirectly affects clavicle (collarbone) movement due to its connection to the scapula. The clavicle and scapula form part of the shoulder girdle. When the serratus protracts or rotates the scapula, it can cause subtle adjustments in the position of the clavicle. This is part of the overall scapuloclavicular rhythm, which is the coordinated movement of the scapula and clavicle during arm movements. However, the serratus anterior does not directly attach to or move the clavicle.

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