Thoracic Muscle Group

Thoracic Muscle Groups

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Table of contents

Introduction

Introduction

The human body is a complex and coordinated structure in which each muscle plays a vital role in movement, breathing, and structural integrity. The pectoral muscles are among the most important muscle groups in the body. They not only contribute to upper body movements and shoulder stability but also play a role in respiration, protect vital organs, and assist in both pushing and pulling actions.

These muscles include superficial muscles such as the pectoralis major and minor, deep muscles like the intercostals, and the diaphragm, which is the body’s primary respiratory muscle. Each of these muscles has its own unique structure, function, and significance. Understanding them is essential not only for athletes, coaches, and physiotherapists but also for anyone who values their physical health.

In this review, we have conducted a detailed analysis of the chest muscles using the renowned reference “Gray’s Anatomy,” one of the most authoritative anatomy books in the world. This analysis covers the names, structures, functions, innervation, strengthening exercises, and common injuries of the thoracic muscles. Gaining this knowledge provides a deeper understanding of the body’s movement mechanisms and can be used to enhance athletic performance, increase strength, and prevent injuries.

Chest Muscles

1. Superficial muscles of the chest

Superficial Thoracic Muscles

Pectoralis major muscle

Pectoralis major Muscle

The pectoralis major is one of the most important muscles of the chest, located at the front of the thorax. It is responsible for various shoulder movements such as adduction, rotation, and elevation of the arm. This muscle plays a key role in pushing exercises like the bench press and push-ups. Strengthening the pectoralis major enhances upper body power, improves chest aesthetics, and increases stability during strength training.

Pectoralis Major

Sections of the Pectoralis Major Muscle

Parts of the Pectoralis Major Muscle

Upper Chest | Clavicular Part

Upper Chest Muscles (Clavicular Head)

The clavicular part of the pectoralis major is located in the upper region of the chest and originates from the inner surface of the clavicle. It extends downward and inward, inserting onto the humerus.

🔹 Function:

  • Its primary role is in shoulder flexion—raising the arm from a low position upward and forward.
  • It also assists in adduction movements, bringing the arm toward the center of the body.
  • It also contributes to internal rotation of the arm.

💪 Effective Exercises:

  • Incline bench press with barbell or dumbbells
  • Incline fly
  • Incline bench press with Smith machine

Special Feature: This section typically has less muscle mass compared to other parts of the chest in most individuals, and it often requires targeted exercises for proper development.

Upper Chest Muscles

Middle Chest | Sternocostal Part

Middle Chest Muscles (Sternocostal Head)

This is the largest and most voluminous part of the pectoralis major. It originates from the anterior surface of the sternum and the cartilage of ribs 1 to 6. The muscle fibers run horizontally and insert into the humerus.

🔹 Function:

  • Adducting the arm toward the body (such as when bringing the arms forward from the sides).
  • Generating power in pressing movements such as the bench press.
  • Assisting in internal rotation of the arm and stabilizing the shoulder.

💪 Effective Exercises:

  • Flat bench press with barbell or dumbbells
  • Flat dumbbell fly
  • Push-ups

Special Feature: This section shows the most muscle growth in bodybuilding routines, as it bears the greatest load during most compound movements like the bench press.

Lower Chest | Abdominal Part

Lower Chest Muscles (Abdominal Head)

This part originates from the anterior rectus sheath or the lower portion of the sternum and the cartilage of the lower ribs (ribs 6 to 7). Its fibers run upward and outward, inserting into the humerus.

🔹 Function:

  • Lowering the arm (shoulder extension from a flexed position), such as when bringing the arm down from an overhead position.
  • Adducting the arm toward the midline of the body, especially during movements where the arm is brought downward and inward.
  • It plays a key role in pressing movements and decline (negative angle) exercises.

💪 Effective Exercises:

  • Decline bench press with barbell or dumbbells
  • Parallel bar dips
  • Low to high cable crossover

Special Feature: This section often shows less development in individuals who don’t train the chest comprehensively, which can result in a flat or unfinished appearance in the lower chest area.

Lower Chest Muscles

Pectoralis Minor Muscle

Pectoralis Minor Muscle

The pectoralis minor is a small but important muscle located beneath the pectoralis major. It plays a key role in the movement and stabilization of the scapula, assisting in upper body motions such as pulling and shoulder rotation. Its primary function is to draw the shoulder downward and stabilize the scapula during both athletic movements and daily activities. Weakness in this muscle can lead to movement dysfunctions in the shoulder and chest.

Pectoralis Minor

Subclavius Muscle

Subclavius Muscle

The subclavius is a small, spindle-shaped muscle located beneath the clavicle. It helps stabilize and move the clavicle, playing an important role in protecting the vital blood vessels and nerves beneath it. Additionally, it reduces stress on the shoulder joint. Weakness or tightness in this muscle can lead to restricted shoulder movement and pain in the clavicle area.

Subclavius Muscle

Serratus Anterior Muscle

Serratus Anterior Muscle

The serratus anterior is one of the most important muscles for scapular stabilization and movement. Named for its saw-toothed shape as it attaches to the ribs, this muscle plays a key role in maintaining scapular balance and stability. It is highly active during forward pushing movements such as throwing, punching, and push-ups. Strengthening the serratus anterior improves shoulder range of motion, increases endurance in athletic activities, and helps prevent shoulder pain and instability.

Serratus anterior muscle
Intercostal Muscles and Diaphragm

2. Deep muscles of the chest

Deep chest muscles

External intercostal muscles

External Intercostals Muscle

The external intercostal muscles are a group of thin, flat muscles located between adjacent ribs. They play a crucial role in the process of inhalation. When these muscles contract, they elevate the ribs and increase the volume of the thoracic cavity, facilitating the entry of air into the lungs.

These muscles also play an important role in stabilizing the chest structure and assisting upper body movements, especially in sports that require deep breathing and thoracic stability.

External intercostal muscles

Internal Intercostal Muscles

Internal Intercostal Muscles

The internal intercostal muscles are a group of thin, flat muscles located beneath the external intercostal muscles and play a crucial role in active exhalation. During deep exhalation, these muscles pull the ribs downward, helping to decrease the volume of the chest cavity.

They also play a key role in maintaining chest stability, protecting internal organs, and assisting upper body movements—especially in sports that require breath control and core strength.

Internal Intercostal Muscles

Innermost Intercostal Muscles

Innermost Intercostal Muscles

The innermost intercostal muscles are the deepest layer of the intercostal muscles, located on the inner surface of the chest wall. They play a role in active exhalation and, together with the internal intercostal muscles, help lower the ribs and decrease the volume of the chest cavity.

Due to their deep position, these muscles receive less attention than the external and internal intercostals, but they are crucial for maintaining chest wall stability and enhancing respiratory function.

Transversus Thoracis Muscle

Transversus Thoracis Muscle

The transversus thoracis muscle is a deep, thin muscle located on the inner wall of the chest cavity, attaching to the sternum. It plays a role in active exhalation by decreasing chest volume and lowering the ribs, thereby assisting in the expulsion of air from the lungs.

In addition to its role in respiration, this muscle helps strengthen the chest wall, stabilize the ribs, and support overall respiratory function during intense physical activities.

Transversus Thoracis Muscle

Subcostal Muscles

Subcostal Muscles

The subcostal muscles are a group of small, deep muscles located on the posterior chest wall, running along the ribs.

These muscles resemble the internal intercostal muscles but are typically found in the posterior part of the chest (behind the ribs). Their role is to assist with exhalation by decreasing chest volume, stabilizing the ribs, and supporting chest movements during respiration.

Subcostal Muscles

Diaphragm Muscle

Diaphragm Muscle

The diaphragm is a thin, dome-shaped muscle that separates the thoracic cavity from the abdominal cavity and is the primary muscle involved in the process of inhalation.

During inhalation, the diaphragm contracts and moves downward, increasing the volume of the chest cavity and allowing air to enter the lungs. During exhalation, the diaphragm relaxes and returns to its original position, aiding in the expulsion of air from the lungs. The diaphragm’s vital roles extend beyond breathing, including supporting the abdominal organs and assisting the circulatory and lymphatic systems.

Diaphragm Muscle

Interesting and Practical Facts

1️⃣ The pectoralis major muscle can generate up to 250 kilograms of force!

✔ In the strongest people in the world, this muscle can lift bench press weights up to 250 kilograms. However, without strength training, it may not even be able to handle 20 kilograms!

2️⃣ A tear in the pectoralis major muscle is one of the most painful sports injuries.

✔ When this muscle tears, it is often accompanied by a "pop" sound or muscle rupture, causing severe bruising, loss of strength, and even muscle deformity. This type of tear commonly occurs in bodybuilders who lift heavy weights during the bench press.

3️⃣ Women also have strong pectoralis major muscles, but they are hidden beneath a layer of fat tissue!

✔ The pectoralis major muscle is the same in both women and men, but in women it is less visible due to fat tissue and mammary glands. Therefore, chest exercises in women enhance the shape and natural lift of the breasts, rather than reducing their size!

4️⃣ The pectoralis major muscle contributes to 35% of daily movements!

✔ From opening doors, putting on clothes, swimming, and throwing a ball to combat movements, this muscle plays a role in most daily activities! So strengthening it isn’t just for aesthetics—it’s highly functional too.

5️⃣ Paralysis of the pectoralis minor muscle can cause impaired shoulder blade (scapular) movement.

✔ The pectoralis minor is a small muscle located beneath the pectoralis major. If this muscle is injured or weak, it can cause movement problems in the shoulder blade and shoulder, which may even affect overall body balance!

6️⃣ Up to 80% of the final shape of the chest muscles is determined by genetics!

✔ Even with the best training program, the shape and attachment of your chest muscle fibers depend largely on your genetics. That’s why some people have wider chests while others have rounder ones.

7️⃣ The pectoralis major muscle affects respiratory function.

✔ During deep breathing, especially in activities like running and swimming, the pectoral muscles help elevate the chest and increase lung capacity. So, if you have breathing difficulties, strengthening your chest muscles might help!

8️⃣ Increasing chest muscle strength also improves pulling power!

✔ Contrary to popular belief that chest muscles only play a role in pressing movements, they also assist the back muscles during pulling actions. That’s why people with strong chests often perform better in pull-ups!

9️⃣ Developing the upper part of the chest is more challenging than the middle and lower sections.

✔ The reason is that the clavicular head contains fewer muscle fibers and they are less frequently engaged. Therefore, to develop this area, you need to perform targeted exercises like incline bench presses.

🔟 Neglecting chest muscle training can lead to poor posture and a rounded, hunched back!

✔ If your back muscles are stronger than your chest muscles, your body tends to pull backward. Conversely, if your chest muscles are stronger than your back muscles, your body leans forward. This muscular imbalance can lead to neck, back, and shoulder pain.

Conclusion

Understanding the chest muscles and their functions not only enhances your grasp of upper body movements and breathing but also improves athletic performance, helps prevent injuries, and boosts overall quality of life.

An examination of these muscles based on Gray’s Anatomy reveals that each muscle plays a specific role in the respiratory system, chest stabilization, and strength movements. From superficial muscles like the pectoralis major to deep muscles such as the diaphragm and intercostals, they all work together in harmony to provide stability, movement, and respiration.

Understanding these structures and performing appropriate exercises is key to improving athletic performance and overall physical health.

Chest Muscles

References

Resources

Anatomy and medical books :

Gray's Anatomy (one of the standard references in anatomy)

Netter's Atlas of Human Anatomy (a well-known illustrated atlas in anatomy)

Clinically Oriented Anatomy by Keith Moore

Medical databases :

PubMed (for scientific and research articles)

MedlinePlus (health and medical information)

WebMD (for practical and general health information)

Sports and training references :

Strength Training Anatomy by Frederic Delavier

Essentials of Strength Training and Conditioning by NSCA

Well-known articles and training programs by international coaches

Medical databases :

PubMed (for scientific and research articles)

MedlinePlus (health and medical information)

WebMD (for practical and general health information)

Images used:
(Kenhub) kenhub.com

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