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The chest is an important part of the body, encompassing vital organs such as the heart and lungs, and enabling us to use our arms. The chest muscles are responsible for moving the arms across the body, up and down, and pushing. The dominant muscle in the upper chest is the pectoralis major, also known as the pec major. This fan-shaped muscle stretches from the armpit to the collarbone and down across the lower chest region on both sides of the chest. The pectoralis minor is a smaller, triangular muscle that lies beneath the pectoralis major and controls structures associated with the back of the body. Other chest muscles include the serratus anterior, the deltoid, and the latissimus dorsi. There are more than 600 muscles in the human body, and they are constantly working to help us move, breathe, and stay alive.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | Over 600 |
| Chest muscles | Pectoralis major, Pectoralis minor, Serratus anterior, Subclavius |
| Pectoralis major | The biggest, strongest, and most dominant muscle in the chest |
| Pectoralis minor | A small, triangular muscle that sits directly underneath the clavicular fibers of the pectoralis major |
| Serratus anterior | A fan-shaped muscle that extends from the lower shoulder to the ribs, also known as the "boxer muscle" |
| Subclavius | A small, triangle-shaped muscle that elevates the clavicle bone during inhalation |
| Main function of chest muscles | Bring arms closer to the body, stabilize the shoulders, lift the arms, and maintain proper posture |
| Common chest injuries | Tendonitis, Torn pectoralis major tendon |
| Chest muscle exercises | Push-ups, Foam roller stretch, Door frame stretch, Dumbbell stretch |
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Pectoralis Major
The pectoralis major is the largest and most dominant muscle in the chest area. It is a thick, fan-shaped muscle that stretches from the armpit to the collarbone and down across the lower chest region on both sides of the chest, with the two sides connecting at the sternum. The pectoralis major is the prime mover of chest-focused or upper-body "push" exercises. It is also responsible for keeping the arms attached to the body and moving each shoulder joint in four distinct directions.
The pectoralis major has two distinct parts, or heads, which originate from different areas: the clavicle and the sternum. The clavicular head is close to the deltoid muscle and contributes to flexion, horizontal adduction, and inward rotation of the humerus. The sternocostal head is the larger of the two heads and contributes to the downward and forward movement of the arm and inward rotation when accompanied by adduction. The sternocostal fibres run more vertically and insert closer to the abdomen. The pectoralis major receives dual motor innervation by the medial pectoral nerve and the lateral pectoral nerve, also known as the lateral anterior thoracic nerve.
The pectoralis major is active during deep or forced inspiration, but not expiration. When the diaphragm and intercostal muscles are insufficient for proper breathing, the pectoralis major can assist in inspiration. It is also used in neck surgery, particularly in flap repairs, due to its size, location, and blood supply.
Injuries to the pectoralis major are rare but can include a torn pectoralis tendon or a complete rupture of the muscle, resulting in severe pain, bruising, and decreased strength.
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Pectoralis Minor
The pectoralis minor is a thin, triangular muscle that sits underneath the pectoralis major. It originates from the margins of the third to fifth ribs, near the costal cartilage, and is crucial in stabilising the scapula by pulling it downward and forward against the thoracic wall. The pectoralis minor also assists with general shoulder and upper arm stability.
The pectoralis minor is one of the most superficial muscles on the anterior aspect of the chest or thoracic wall. It is located deep to the pectoralis major muscle. Together with the pectoralis major, the pectoralis minor forms the anterior wall of the axilla. The pectoralis minor is also related to the serratus anterior and intercostal muscles, the ribs, and several neurovascular and lymphatic structures.
The primary nerve supply to the pectoralis minor comes via the medial pectoral nerve (C8, T1), a minor branch of the brachial plexus that arises from the cervical portion of the spinal cord. The pectoralis minor also receives innervation from the lateral pectoral nerve, via a communicating branch known as the 'ansa pectoralis'. This results in the pectoralis minor receiving innervation from the spinal roots of C5-T1.
The pectoralis minor is important clinically and as a surgical landmark due to the structures that lie below or deep to the muscle and its tendon. Running deep to the pectoralis minor muscle are the nerves and blood supply to the upper limb: the posterior, lateral, and medial cords of the brachial plexus. The pectoralis minor is used as the reference point for the three divisions of the axillary artery.
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Serratus Anterior
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 then wraps around the ribcage, passing beneath the scapula to insert on the underside of the scapula on its medial border. The serratus anterior is also referred to as the "boxer's muscle" or the "big swing muscle" because it enables a long and strong reach, such as when throwing a punch. It is the prime mover in scapular protraction and scapular upward rotation, and it is a key scapular stabiliser, keeping the shoulder blades against the ribcage when at rest and during movement.
The serratus anterior is divided into three parts according to the points of insertion: serratus anterior superior (insertion near the superior angle), serratus anterior intermediate (insertion along the medial border), and serratus anterior inferior (insertion near the inferior angle). The serratus anterior inferior is responsible for the anterolateral motion of the scapula, which allows for arm elevation. When the shoulder girdle is fixed, all three parts of the serratus anterior muscle work together to lift the ribs, assisting with respiration.
The serratus anterior acts in concert with the upper and lower fibres of the trapezius muscle to sustain upward rotation of the scapula, which allows for overhead lifting. It is also involved in pulling the scapula forward and around the rib cage, which is important for movements such as throwing a punch.
The serratus anterior is a key muscle for athletes, particularly in sports with repetitive motions such as swimming, tennis, or weightlifting. It is vulnerable to injury, especially during certain types of surgery, and pain may result from tension, stress, or overuse.
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Subclavius
The subclavius is a small, triangular muscle in the anterior thorax located between the clavicle and the first rib. It originates from the first rib and inserts on the undersurface of the middle third of the clavicle. The subclavius is enveloped in the clavipectoral fascia, a fibrous connective tissue that spans the interval between the clavicle and pectoralis minor muscle. The pectoralis major muscle is situated superficially to the subclavius and clavipectoral fascia.
The subclavius muscle is responsible for actively stabilising the clavicle at the sternoclavicular joint during movements of the shoulder and arm. It helps to prevent dislocation of the clavicle and protects the neurovascular structures beneath it in the event of a fracture. The main blood supply to the subclavius is provided by the clavicular branch of the thoracoacromial artery, with additional contributions from the suprascapular artery.
The subclavius is innervated by the nerve to the subclavius, also known as the subclavian nerve, which arises from the superior trunk of the brachial plexus. Specifically, the nerve originates from the C5-C6 nerve roots. The presence of a dedicated branch of the brachial plexus that is not shared by any other muscle suggests that the subclavius plays a crucial role in providing information about the upper extremity.
Myofascial pain or strain in the subclavius muscle can result in discomfort along the clavicle, sternoclavicular joint, shoulder, or even radiating into the arm. Heavy lifting, chronic forward shoulder positioning, carrying a heavy backpack or sleeping with the arm overhead are some of the activities that may contribute to pain in this muscle.
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Latissimus Dorsi
The latissimus dorsi is a large, flat muscle on the back that stretches to the sides, behind the arm, and is partly covered by the trapezius on the back near the midline. The word "latissimus dorsi" comes from Latin and means "broadest [muscle] of the back". The pair of muscles are commonly known as "lats", especially among bodybuilders. The latissimus dorsi is responsible for extension, adduction, transverse extension (also known as horizontal abduction or horizontal extension), flexion from an extended position, and (medial) internal rotation of the shoulder joint. It also plays a role in the extension and lateral flexion of the lumbar spine.
The latissimus dorsi is innervated by the sixth, seventh, and eighth cervical nerves through the thoracodorsal (long subscapular) nerve. It is supplied predominantly by the thoracodorsal artery, a continuation of the subscapular artery, which is a branch of the third part of the axillary artery. The thoracodorsal artery and its venae comitantes enter the muscle at a single point on the anterior surface of the muscle, 6 cm to 12 cm from the bifurcation of the subscapular artery and 1 cm to 4 cm medial to the lateral margin of the muscle. In addition to the thoracodorsal artery, the latissimus dorsi also receives blood supply from the dorsal perforating branches of the inferior three posterior intercostal arteries and the superior three lumbar arteries.
The number of dorsal vertebrae to which the latissimus dorsi is attached varies from four to eight, and the number of costal attachments can also vary. The latissimus dorsi crosses the inferior angle of the scapula, and fibres from the muscle may originate from the scapula. The latissimus dorsi is considered an extrinsic muscle of the back, meaning it originates from the myogenic cells in the developing upper limb buds rather than from the myotomal dorsal epaxial division of the somite. Embryologically, the latissimus dorsi and teres major muscles are closely related as they both originate from the pre-muscle sheath of the arm.
The latissimus dorsi works collaboratively with the teres major and pectoralis major muscles to perform actions of the upper extremity. Together, these muscles work to adduct, medially rotate, and extend the arm at the glenohumeral joint. The latissimus dorsi also assists in depressing the arm with the teres major and pectoralis major.
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Frequently asked questions
The chest is dominated by two muscles: the pectoralis major and the pectoralis minor, known collectively as the pecs. The pectoralis major is the larger and stronger of the two, and the pectoralis minor sits directly underneath it.
The chest muscles' main function is to bring the arms closer to the body, but they also assist with moving the shoulders and rotating the arms. They also help with breathing.
The classic push-up is a great way to strengthen the chest, but it's often performed incorrectly, causing pain. Other exercises that can help strengthen the chest include the bench press and barbell press.
