Pectoralis major muscle
Encyclopedia
The pectoralis major is a thick, fan-shaped muscle
, situated at the chest (anterior) of the body. It makes up the bulk of the chest muscles in the male and lies under the breast
in the female. Underneath the pectoralis major is the pectoralis minor, a thin, triangular muscle.
The sensory feedback from the pectoralis major follows the reverse path, returning via first-order neurons to the spinal nerves at C5, C6, C8, and T1 through the anterior rami. After the synapse in the posterior horn of the spinal cord, sensory information concerning movement of the muscle, proprioception, and pressure then travels through a second-order neuron in the posterior corticospinal track to the medulla. There, the fibers decussate to form the medial lemniscus which carries the sensory information the rest of the way to the thalamus, the “gateway to the cortex”. The thalamus diverts some sensory information to the cerebellum and the basal nuclei to complete the motor feedback loop while some sensory information ascends directly to the postcentral gyrus of the parietal lobe of the brain via third-order neurons. Sensory information for the pectoralis major is processed in the superior portion of the sensory homunculus, adjacent to the longitudinal fissure which divides the two hemispheres of the brain.
These deep fibers, and particularly those from the lower costal cartilages, ascend the higher, turning backward successively behind the superficial and upper ones, so that the tendon appears to be twisted.
The posterior lamina reaches higher on the humerus than the anterior one, and from it an expansion is given off which covers the intertubercular groove of the humerus
and blends with the capsule of the shoulder-joint.
From the deepest fibers of this lamina at its insertion an expansion is given off which lines the intertubercular groove, while from the lower border of the tendon a third expansion passes downward to the fascia
of the arm.
part or its absence, greater or less extent of separation of sternocostal and clavicular
parts, fusion of clavicular part with deltoid
, and decussation
in front of the sternum.
Deficiency or absence of the sternocostal part is not uncommon.
Absence of the clavicular part is less frequent.
Rarely, the whole muscle is missing. This may accompany absence of the breast in females. (See Poland syndrome
).
and contributes to flexion, horizontal adduction, and inward rotation of the humerus. When at an approximately 110 degree angle, it contributes to abduction of the humerus. The sternocostal part is antagonistic to the clavicular part contributing to downward and forward movement of the arm and inward rotation when accompanied by adduction. The sternal fibers can also contribute to extension, but not beyond anatomical position.
ing (using dumbbell
s, barbell
s or machines at various angles such as decline, incline and flat where the hips are above, below and level with the head respectively), push ups, flyes
(using dumbbells or machines at either flat or inclined angles), cable crossovers
or dips
. Multi-joint press exercises are better for building muscle mass, while fly and crossovers are more suited for shaping and increasing striations
. This muscle is often said to consist of four portions (Upper, Lower, Inner and Outer) but the pectoralis actually contracts evenly across all heads during most exercises and as such no portion can be 'targeted'.
The pectoralis can also be trained through a variety of sports as well as by all four Olympic styles of swimming, i.e. the butterfly
, backstroke
, breaststroke
and front crawl
. The anaerobic
work capacity of the pectoralis is a major determinant of swimming speed, whereas swimming endurance is more influenced by the aerobic capacity of the deltoid muscle
(apart from overall cardiopulmonary aerobic capacity).
can also be used in its place.
is a congenital anomaly in which there is a malformation of the chest causing the pectoralis major on one side of the body to be absent. Other characteristics of this disease are "unilateral shortening of the index, long, and ring fingers, syndactyly of the affected digits, hypoplasia of the hand, and the absence of the sternocostal portion of the ipsilateral pectoralis major muscle". Although the absence of a pectoralis major is not life threatening, it will have an effect on the person with Poland’s Syndrome. Adduction and medial rotation of the arm will be much harder to accomplish without the pectoralis major. The latissimus dorsi and teres major also aid in adduction and medial rotation of the arm, so they may be able to compensate for the lack of extra muscle. However, some patients with Poland’s Syndrome may also be lacking these muscles, which make these actions nearly impossible.
Researchers from the Department of Rehabilitation Medicine at the Yonsei University College of Medicine in Seoul
, Korea
reported a case of congenital absence of pectoralis major in 1990. According to Kakulas and Adams, pectoralis major is the most frequently congenitally absent muscle. The case involved a 22 year old marine who had asymmetrical configuration of chest wall who had never experienced difficulties performing daily activities, but who experienced difficulties in the military camp
. He had difficulty in some training activities especially those such as throwing a grenade
or rope climbing
. During a surgery performed to correct the sternal depression, it was found that the right pectoralis major was totally absent. However, previous physical exams did not show deficiencies in muscle strength as the right shoulder was good for flexion
, adduction
, horizontal adduction and internal rotation. Moreover, his pain and touch sensation were normal. X-rays were also performed and showed normal pictures of the chest's bones. The fact that the absence of pectoralis major did not cause functional loss in ordinary activities in this case of congenital absence showed that other surrounding muscles played a compensation role.
tumors as they look like enlargements of the breasts. They are well-encapsulated radiolucent tumours of fat density. Their location can be accurately identified through computed tomography
and magnetic resonance imaging
(MRI). The treatment in these cases involves complete surgical excision because of the risk of liposarcoma they post especially large intramuscular liposomas. Partial excision is risky because recurrence may occur.
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
, situated at the chest (anterior) of the body. It makes up the bulk of the chest muscles in the male and lies under the breast
Breast
The breast is the upper ventral region of the torso of a primate, in left and right sides, which in a female contains the mammary gland that secretes milk used to feed infants.Both men and women develop breasts from the same embryological tissues...
in the female. Underneath the pectoralis major is the pectoralis minor, a thin, triangular muscle.
Innervation
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. One route of innervation of the pectoralis major originates in the C7, C8 and T1 nerve roots which merge to form the lower trunk of the brachial plexus. The fibers continue in the anterior division of the lower trunk, become the medial cord, and exit the medial cord as the medial pectoral nerve. The medial pectoral nerve then communicates the action potential across the neuromuscular junction by releasing acetylcholine into the neuromuscular junction, inciting a proportional muscle contraction of the sternal head of the pectoralis major. The second source of innervation of the pectoralis major originates from the C5 and C6 nerve roots which merge to form the upper trunk, splits off into the anterior division of the upper trunk which joins with the middle trunk to form the lateral cord. The lateral pectoral nerve branches off of the lateral cord of the brachial plexus and is distributed over the deep surface of the pectoralis major. At the neuromuscular junction, the lateral pectoral nerve provides motor input to the clavicular head of the pectoralis major.The sensory feedback from the pectoralis major follows the reverse path, returning via first-order neurons to the spinal nerves at C5, C6, C8, and T1 through the anterior rami. After the synapse in the posterior horn of the spinal cord, sensory information concerning movement of the muscle, proprioception, and pressure then travels through a second-order neuron in the posterior corticospinal track to the medulla. There, the fibers decussate to form the medial lemniscus which carries the sensory information the rest of the way to the thalamus, the “gateway to the cortex”. The thalamus diverts some sensory information to the cerebellum and the basal nuclei to complete the motor feedback loop while some sensory information ascends directly to the postcentral gyrus of the parietal lobe of the brain via third-order neurons. Sensory information for the pectoralis major is processed in the superior portion of the sensory homunculus, adjacent to the longitudinal fissure which divides the two hemispheres of the brain.
Laminae
This tendon consists of two laminae, placed one in front of the other, and usually blended together below.- The anterior lamina, which is thicker, receives the clavicular and the uppermost sternal fibers. They are inserted in the same order as that in which they arise: the most lateral of the clavicular fibers are inserted at the upper part of the anterior lamina; the uppermost sternal fibers pass down to the lower part of the lamina which extends as low as the tendon of the DeltoidDeltoid muscleIn human anatomy, the deltoid muscle is the muscle forming the rounded contour of the shoulder. Anatomically, it appears to be made up of three distinct sets of fibers though electromyography suggests that it consists of at least seven groups that can be independently coordinated by the central...
and joins with it. - The posterior lamina of the tendon receives the attachment of the greater part of the sternal portion and the deep fibers, i. e., those from the costal cartilagesCostal cartilagesThe costal cartilages are bars of hyaline cartilage which serve to prolong the ribs forward and contribute very materially to the elasticity of the walls of the thorax.-Differences from 1-12:...
.
These deep fibers, and particularly those from the lower costal cartilages, ascend the higher, turning backward successively behind the superficial and upper ones, so that the tendon appears to be twisted.
The posterior lamina reaches higher on the humerus than the anterior one, and from it an expansion is given off which covers the intertubercular groove of the humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
and blends with the capsule of the shoulder-joint.
From the deepest fibers of this lamina at its insertion an expansion is given off which lines the intertubercular groove, while from the lower border of the tendon a third expansion passes downward to the fascia
Fascia
A fascia is a layer of fibrous tissue that permeates the human body. A fascia is a connective tissue that surrounds muscles, groups of muscles, blood vessels, and nerves, binding those structures together in much the same manner as plastic wrap can be used to hold the contents of sandwiches...
of the arm.
Variations
The more frequent variations include greater or less extent of attachment to the ribs and sternum, varying size of the abdominalAbdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
part or its absence, greater or less extent of separation of sternocostal and clavicular
Clavicle
In human anatomy, the clavicle or collar bone is a long bone of short length that serves as a strut between the scapula and the sternum. It is the only long bone in body that lies horizontally...
parts, fusion of clavicular part with deltoid
Deltoid
Deltoid can refer to:* The deltoid muscle, a muscle in the shoulder* Kite , also known as a deltoid, a type of quadrilateral* A deltoid curve, a three-sided hypocycloid* A leaf shape* The deltoid tuberosity, a part of the humerus...
, and decussation
Decussation
Decussation is used in biological contexts to describe a crossing.Examples include:* In the brain, where nerve fibers obliquely cross from one lateral part to the other, that is to say they cross at a level other than their origin...
in front of the sternum.
Deficiency or absence of the sternocostal part is not uncommon.
Absence of the clavicular part is less frequent.
Rarely, the whole muscle is missing. This may accompany absence of the breast in females. (See Poland syndrome
Poland syndrome
Poland syndrome is a rare birth defect characterized by underdevelopment or absence of the chest muscle on one side of the body and webbing of the fingers of the hand on the same side mostly common on the right...
).
Actions
The pectoralis major has four actions which are primarily responsible for movement of the shoulder joint. The first action is flexion of the humerus, as in throwing a ball side-arm, and in lifting a child. Secondly, it adducts the humerus, as when flapping the arms. Thirdly, it rotates the humerus medially, as occurs when arm-wrestling. Finally it aids in deep inspiration, as in taking a deep breath before jumping in a pool. The pectoralis major is also responsible for keeping the arm attached to the trunk of the body. It has two different parts which are responsible for different actions. The clavicular part is close to the deltoid muscleDeltoid muscle
In human anatomy, the deltoid muscle is the muscle forming the rounded contour of the shoulder. Anatomically, it appears to be made up of three distinct sets of fibers though electromyography suggests that it consists of at least seven groups that can be independently coordinated by the central...
and contributes to flexion, horizontal adduction, and inward rotation of the humerus. When at an approximately 110 degree angle, it contributes to abduction of the humerus. The sternocostal part is antagonistic to the clavicular part contributing to downward and forward movement of the arm and inward rotation when accompanied by adduction. The sternal fibers can also contribute to extension, but not beyond anatomical position.
Training
A variety of resistance exercises can be used to train the pectoralis major, including bench pressBench press
The bench press is an exercise of the upper body. For bodybuilding purposes, it is used to stimulate the pectorals, deltoids, and triceps. While on his or her back, the person performing the bench press lowers a weight to the level of the chest, then pushes it back up until the arm is straight...
ing (using dumbbell
Dumbbell
The dumbbell, a type of free weight, is a piece of equipment used in weight training. It can be used individually or in pairs .-History:...
s, barbell
Barbell
A barbell is a piece of exercise equipment used in weight training, weightlifting and powerlifting. Barbells range in length from to although bars above 7' in length are used primarily by powerlifters and aren't commonplace...
s or machines at various angles such as decline, incline and flat where the hips are above, below and level with the head respectively), push ups, flyes
Fly (exercise)
A fly is a strength training exercise in which the hand and arm move through an arc while the elbow is kept at a constant angle. Flyes are used to work the muscles of the upper body...
(using dumbbells or machines at either flat or inclined angles), cable crossovers
Cable machine
A cable machine is an item of equipment used in weight training or functional training. It consists of a rectangular, vertically-oriented steel frame about 3 metres wide and 2 metres high, with a weight stack at each end. The cables that connect the handles to the weight stacks run through...
or dips
Dip (exercise)
The dip is an exercise used in strength training. Normal, shoulder-width dips primarily train the triceps, with major synergists being the anterior deltoid, the pectoralis muscles , and the rhomboid muscles of the back...
. Multi-joint press exercises are better for building muscle mass, while fly and crossovers are more suited for shaping and increasing striations
Striated muscle
Striated muscle tissue is a form of fibers that are combined into parallel fibers. More specifically, it can refer to:* Cardiac muscle .* Skeletal muscle* Branchiomeric muscles...
. This muscle is often said to consist of four portions (Upper, Lower, Inner and Outer) but the pectoralis actually contracts evenly across all heads during most exercises and as such no portion can be 'targeted'.
The pectoralis can also be trained through a variety of sports as well as by all four Olympic styles of swimming, i.e. the butterfly
Butterfly stroke
The butterfly is a swimming stroke swum on the breast, with both arms moving simultaneously. The butterfly kick was developed separately, and is also known as the "dolphin kick"...
, backstroke
Backstroke
The backstroke, also sometimes called the back crawl, is one of the four swimming styles regulated by FINA, and the only regulated style swum on the back. This has the advantage of easy breathing, but the disadvantage of swimmers not being able to see where they are going. It is also the only...
, breaststroke
Breaststroke
The breaststroke is a swimming style in which the swimmer is on his or her chest and the torso does not rotate. It is the most popular recreational style due to its stability and the ability to keep the head out of the water a large portion of the time. In most swimming classes, beginners learn...
and front crawl
Front crawl
The front crawl, forward crawl, or freestyle is a swimming stroke usually regarded as the fastest of the four front primary strokes. As such, the front crawl stroke is nearly universally used during a freestyle swimming competition, hence the synonymously used term "freestyle". It is one of two...
. The anaerobic
Anaerobic exercise
Anaerobic exercise is exercise intense enough to trigger anaerobic metabolism. It is used by athletes in non-endurance sports to promote strength, speed and power and by body builders to build muscle mass...
work capacity of the pectoralis is a major determinant of swimming speed, whereas swimming endurance is more influenced by the aerobic capacity of the deltoid muscle
Deltoid muscle
In human anatomy, the deltoid muscle is the muscle forming the rounded contour of the shoulder. Anatomically, it appears to be made up of three distinct sets of fibers though electromyography suggests that it consists of at least seven groups that can be independently coordinated by the central...
(apart from overall cardiopulmonary aerobic capacity).
Injuries and Imaging
Pectoralis major muscle tears are an uncommon sporting injury, most commonly seen in weightlifters, wrestlers and footballers. The injury is characterized by pain in the chest wall, bruising and loss of strength of the muscle. High grade partial or full thickness tears warrant surgery if function is to be preserved, particularly in the athletic population. MRI is the best imaging test to confirm the diagnosis, location and extent of a tear, though in experienced hands, ultrasoundUltrasound
Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...
can also be used in its place.
Poland's Syndrome
Poland’s SyndromePoland syndrome
Poland syndrome is a rare birth defect characterized by underdevelopment or absence of the chest muscle on one side of the body and webbing of the fingers of the hand on the same side mostly common on the right...
is a congenital anomaly in which there is a malformation of the chest causing the pectoralis major on one side of the body to be absent. Other characteristics of this disease are "unilateral shortening of the index, long, and ring fingers, syndactyly of the affected digits, hypoplasia of the hand, and the absence of the sternocostal portion of the ipsilateral pectoralis major muscle". Although the absence of a pectoralis major is not life threatening, it will have an effect on the person with Poland’s Syndrome. Adduction and medial rotation of the arm will be much harder to accomplish without the pectoralis major. The latissimus dorsi and teres major also aid in adduction and medial rotation of the arm, so they may be able to compensate for the lack of extra muscle. However, some patients with Poland’s Syndrome may also be lacking these muscles, which make these actions nearly impossible.
Researchers from the Department of Rehabilitation Medicine at the Yonsei University College of Medicine in Seoul
Seoul
Seoul , officially the Seoul Special City, is the capital and largest metropolis of South Korea. A megacity with a population of over 10 million, it is the largest city proper in the OECD developed world...
, Korea
Korea
Korea ) is an East Asian geographic region that is currently divided into two separate sovereign states — North Korea and South Korea. Located on the Korean Peninsula, Korea is bordered by the People's Republic of China to the northwest, Russia to the northeast, and is separated from Japan to the...
reported a case of congenital absence of pectoralis major in 1990. According to Kakulas and Adams, pectoralis major is the most frequently congenitally absent muscle. The case involved a 22 year old marine who had asymmetrical configuration of chest wall who had never experienced difficulties performing daily activities, but who experienced difficulties in the military camp
Military camp
A military camp or bivouac is a semi-permanent facility for the lodging of an army. Camps are erected when a military force travels away from a major installation or fort during training or operations, and often have the form of large campsites. In the Roman era the military camp had highly...
. He had difficulty in some training activities especially those such as throwing a grenade
Grenade
A grenade is a small explosive device that is projected a safe distance away by its user. Soldiers called grenadiers specialize in the use of grenades. The term hand grenade refers any grenade designed to be hand thrown. Grenade Launchers are firearms designed to fire explosive projectile grenades...
or rope climbing
Rope climbing
Rope climbing is a sport in which competitors, usually men, attempt to climb up a suspended vertical rope using only their hands. Rope climbing is practised regularly at the World Police and Fire Games, and is enjoying a resurgence in France, where competitions are held in shopping centres...
. During a surgery performed to correct the sternal depression, it was found that the right pectoralis major was totally absent. However, previous physical exams did not show deficiencies in muscle strength as the right shoulder was good for flexion
Flexion
In anatomy, flexion is a position that is made possible by the joint angle decreasing. The skeletal and muscular systems work together to move the joint into a "flexed" position. For example the elbow is flexed when the hand is brought closer to the shoulder...
, adduction
Adduction
Adduction is a movement which brings a part of the anatomy closer to the middle sagittal plane of the body. It is opposed to abduction.-Upper limb:* of arm at shoulder ** Subscapularis** Teres major** Pectoralis major** Infraspinatus...
, horizontal adduction and internal rotation. Moreover, his pain and touch sensation were normal. X-rays were also performed and showed normal pictures of the chest's bones. The fact that the absence of pectoralis major did not cause functional loss in ordinary activities in this case of congenital absence showed that other surrounding muscles played a compensation role.
Other diseases
Pectoralis major muscle in rare occasions may develop intramuscular lipomas. Such rare tumors may mimic malignant breastBreast
The breast is the upper ventral region of the torso of a primate, in left and right sides, which in a female contains the mammary gland that secretes milk used to feed infants.Both men and women develop breasts from the same embryological tissues...
tumors as they look like enlargements of the breasts. They are well-encapsulated radiolucent tumours of fat density. Their location can be accurately identified through computed tomography
Computed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
and magnetic resonance imaging
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
(MRI). The treatment in these cases involves complete surgical excision because of the risk of liposarcoma they post especially large intramuscular liposomas. Partial excision is risky because recurrence may occur.
See also
- Tra TelligmanTra TelligmanTracy Telligman is a retired American mixed martial artist and boxer who has fought in Japan, Russia and the USA...
, a MMAMixed martial artsMixed Martial Arts is a full contact combat sport that allows the use of both striking and grappling techniques, both standing and on the ground, including boxing, wrestling, Brazilian jiu-jitsu, muay Thai, kickboxing, karate, judo and other styles. The roots of modern mixed martial arts can be...
Fighter who lost his right pectoral muscle in an accident as a child.