The deltoid muscle is the

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

forming the rounded contour of the human shoulder. It is also known as the 'common shoulder muscle', particularly in other animals such as the domestic

cat The cat (''Felis catus''), also referred to as the domestic cat or house cat, is a small domesticated carnivorous mammal. It is the only domesticated species of the family Felidae. Advances in archaeology and genetics have shown that the ...

. Anatomically, the deltoid muscle is made up of three distinct sets of

muscle fibers Skeletal muscle (commonly referred to as muscle) is one of the three types of vertebrate muscle tissue, the others being cardiac muscle and smooth muscle. They are part of the somatic nervous system, voluntary muscular system and typically are a ...

, namely the # anterior or clavicular part (pars clavicularis) ( More commonly known as the front delt.) # posterior or scapular part (pars scapularis) ( More commonly known as the rear delt.) # intermediate or acromial part (pars acromialis) ( More commonly known as the side delt) The deltoid's fibres are

pennate muscle A pennate or pinnate muscle (also called a penniform muscle) is a type of skeletal muscle with fascicles that attach obliquely (in a slanting position) to its tendon. This type of muscle generally allows higher force production but a smaller ra ...

. However,

electromyography Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram. An electromyo ...

suggests that it consists of at least seven groups that can be independently coordinated by the

nervous system In biology, the nervous system is the complex system, highly complex part of an animal that coordinates its behavior, actions and sense, sensory information by transmitting action potential, signals to and from different parts of its body. Th ...

. It was previously called the deltoideus (plural ''deltoidei'') and the name is still used by some anatomists. It is called so because it is in the shape of the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

capital letter

delta Delta commonly refers to: * Delta (letter) (Δ or δ), the fourth letter of the Greek alphabet * D (NATO phonetic alphabet: "Delta"), the fourth letter in the Latin alphabet * River delta, at a river mouth * Delta Air Lines, a major US carrier ...

(Δ). Deltoid is also further shortened in

slang A slang is a vocabulary (words, phrases, and linguistic usages) of an informal register, common in everyday conversation but avoided in formal writing and speech. It also often refers to the language exclusively used by the members of pa ...

as "delt". A study of 30 shoulders revealed an average mass of in humans, ranging from to .

Structure

Origin

# The

anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

or clavicular fibers arise from most of the anterior border and upper surface of the lateral third of the clavicle. Retrieved January 2012. The anterior origin lies adjacent to the lateral fibers of the '' pectoralis major'' muscle as do the end tendons of both muscles. These muscle fibers are closely related and only a small chiasmatic space, through which the

cephalic vein In human anatomy, the cephalic vein (also called the antecubital vein) is a superficial vein in the arm. It is the longest vein of the upper limb. It starts at the anatomical snuffbox from the radial end of the dorsal venous network of hand, a ...

passes, prevents the two muscles from forming a continuous muscle mass. # Intermediate or acromial fibers arise from the superior surface of the

acromion In human anatomy, the acromion (from Greek: ''akros'', "highest", ''ōmos'', "shoulder", : acromia) or summit of the shoulder is a bony process on the scapula (shoulder blade). Together with the coracoid process, it extends laterally over the sh ...

process of the

scapula The scapula (: scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on either side ...

. # Posterior or spinal fibers arise from the lower lip of the posterior border of the

spine of the scapula The spine of the scapula or scapular spine is a prominent plate of bone, which crosses obliquely the medial four-fifths of the scapula at its upper part, and separates the supra- from the infraspinatous fossa. Structure It begins at the vertica ...

Insertion

From this extensive origin the fibers converge toward their insertion on the

deltoid tuberosity In human anatomy, the deltoid tuberosity is a rough, triangular area on the anterolateral (front-side) surface of the middle of the humerus. It is a site of attachment of deltoid muscle. Structure Variation The deltoid tuberosity has been r ...

on the middle of the

lateral Lateral is a geometric term of location which may also refer to: Biology and healthcare * Lateral (anatomy), a term of location meaning "towards the side" * Lateral cricoarytenoid muscle, an intrinsic muscle of the larynx * Lateral release ( ...

aspect of the shaft of the

humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

; the intermediate fibers passing vertically, the anterior obliquely backward and laterally, and the posterior obliquely forward and laterally. Though traditionally described as a single insertion, the deltoid insertion is divided into two or three discernible areas corresponding to the muscle's three areas of origin. The insertion is an arch-like structure with strong anterior and posterior fascial connections flanking an intervening tissue bridge. It additionally gives off extensions to the deep brachial fascia. Furthermore, the deltoid fascia contributes to the brachial fascia and is connected to the

medial Medial may refer to: Mathematics * Medial magma, a mathematical identity in algebra Geometry * Medial axis, in geometry the set of all points having more than one closest point on an object's boundary * Medial graph, another graph that repr ...

and lateral intermuscular septa.

Blood supply

The deltoid is supplied by the thoracoacromial artery (acromial and deltoid branches), the circumflex humeral arteries, and the

profunda brachii artery The deep artery of arm (also known as deep brachial artery) is a large artery of the arm which arises from the brachial artery. It descends in the arm before ending by anastomosing with the radial recurrent artery. Structure Origin The deep ...

(deltoid branch).

Nerve supply

The deltoid is innervated by the

axillary nerve The axillary nerve or the circumflex nerve is a nerve of the human body, that originates from the brachial plexus ( upper trunk, posterior division, posterior cord) at the level of the axilla (armpit) and carries nerve fibers from C5 and C6. ...

. The axillary nerve originates from the

anterior rami The ventral ramus (: rami) (Latin for 'branch') is the anterior division of a spinal nerve. The ventral rami supply the antero-lateral parts of the trunk and the limbs. They are mainly larger than the dorsal rami. Shortly after a spinal nerve e ...

of the

cervical nerves A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into ...

C5 and C6, via the superior trunk, posterior division of the superior trunk, and the posterior cord of the

brachial plexus The brachial plexus is a network of nerves (nerve plexus) formed by the anterior rami of the lower four Spinal nerve#Cervical nerves, cervical nerves and first Spinal nerve#Thoracic nerves, thoracic nerve (cervical spinal nerve 5, C5, Cervical spi ...

Studies have shown that there are seven neuromuscular segments to the deltoid muscle. Three of these lie in the anatomical anterior head of the deltoid, one in the anatomical middle head, and three in the anatomical posterior head of the deltoid. These neuromuscular segments are supplied by smaller branches of the axillary nerve, and work in coordination with other muscles of the shoulder girdle include pectoralis major and supraspinatus. The axillary nerve is sometimes damaged during surgical procedures of the

axilla The axilla (: axillae or axillas; also known as the armpit, underarm or oxter) is the area on the human body directly under the shoulder joint. It includes the axillary space, an anatomical space within the shoulder girdle between the arm a ...

, such as for

breast cancer Breast cancer is a cancer that develops from breast tissue. Signs of breast cancer may include a Breast lump, lump in the breast, a change in breast shape, dimpling of the skin, Milk-rejection sign, milk rejection, fluid coming from the nipp ...

. It may also be injured by anterior dislocation of the head of the humerus. Structures under deltoid *

Humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

Pectoralis minor Pectoralis minor muscle () is a thin, triangular muscle, situated at the upper part of the chest, beneath the pectoralis major in the human body. It arises from ribs III-V; it inserts onto the coracoid process of the scapula. It is innervated by ...

Supraspinatus The supraspinatus (: supraspinati) is a relatively small muscle of the upper back that runs from the supraspinous fossa superior portion of the scapula (shoulder blade) to the greater tubercle of the humerus. It is one of the four rotator cuff m ...

Infraspinatus In human anatomy, the infraspinatus muscle is a thick triangular muscle, which occupies the chief part of the infraspinatous fossa.''Gray's Anatomy'', see infobox. As one of the four muscles of the rotator cuff, the main function of the infraspin ...

* Teres minor *

Subscapularis The subscapularis is a large triangular muscle which fills the subscapular fossa and inserts into the lesser tubercle of the humerus and the front of the capsule of the Glenohumeral joint, shoulder-joint. Structure The subscapularis is covere ...

* Pectoralis major *

Teres major The teres major muscle is a muscle of the upper limb. It attaches to the scapula and the humerus and is one of the seven scapulohumeral muscles. It is a thick but somewhat flattened muscle. The teres major muscle (from Latin ''teres'', meanin ...

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 (plural: ''latissimi dorsi'') comes from L ...

coracobrachialis The coracobrachialis muscle muscle in the upper medial part of the arm. It is located within the anterior compartment of the arm. It originates from the coracoid process of the scapula; it inserts onto the middle of the medial aspect of the body ...

Biceps brachii The biceps or biceps brachii (, "two-headed muscle of the arm") is a large muscle that lies on the front of the upper arm between the shoulder and the elbow. Both heads of the muscle arise on the scapula and join to form a single muscle bell ...

Triceps brachii The triceps, or triceps brachii (Latin for "three-headed muscle of the arm"), is a large muscle on the back of the upper limb of many vertebrates. It consists of three parts: the medial, lateral, and long head. All three heads cross the elbow jo ...

* Anterior circumflex humeral vessels * Posterior circumflex humeral vessels *

Axillary nerve The axillary nerve or the circumflex nerve is a nerve of the human body, that originates from the brachial plexus ( upper trunk, posterior division, posterior cord) at the level of the axilla (armpit) and carries nerve fibers from C5 and C6. ...

Shoulder joint The shoulder joint (or glenohumeral joint from Greek ''glene'', eyeball, + -''oid'', 'form of', + Latin ''humerus'', shoulder) is structurally classified as a synovial joint, synovial ball-and-socket joint and functionally as a diarthrosis and m ...

Rotator cuff The rotator cuff (SITS muscles) is a group of muscles and their tendons that act to stabilize the human shoulder and allow for its extensive range of motion. Of the seven scapulohumeral muscles, four make up the rotator cuff. The four muscles a ...

* Coracoacromial ligament

Function

When all its fibers contract simultaneously, the deltoid is the prime mover of arm abduction along the frontal plane. The arm must be medially rotated for the deltoid to have maximum effect. This makes the deltoid an antagonist muscle of the ''pectoralis major ''and ''

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 (plural: ''latissimi dorsi'') comes from L ...

'' during arm adduction. The anterior fibers assist the ''pectoralis major'' to flex the shoulder. The anterior deltoid also works in tandem with the

subscapularis The subscapularis is a large triangular muscle which fills the subscapular fossa and inserts into the lesser tubercle of the humerus and the front of the capsule of the Glenohumeral joint, shoulder-joint. Structure The subscapularis is covere ...

, pecs and lats to internally (medially) rotate the humerus. The intermediate fibers perform basic shoulder abduction when the shoulder is internally rotated, and perform shoulder transverse abduction when the shoulder is externally rotated. They are not utilized significantly during strict transverse extension (shoulder internally rotated) such as in rowing movements, which use the posterior fibers. The posterior fibers assist the ''

'' to extend the shoulder. Other transverse extensors, the ''

infraspinatus In human anatomy, the infraspinatus muscle is a thick triangular muscle, which occupies the chief part of the infraspinatous fossa.''Gray's Anatomy'', see infobox. As one of the four muscles of the rotator cuff, the main function of the infraspin ...

'' and '' teres minor'', also work in tandem with the posterior deltoid as external (lateral) rotators, antagonists to strong internal rotators like the pecs and lats. An important function of the deltoid in humans is preventing the

dislocation In materials science, a dislocation or Taylor's dislocation is a linear crystallographic defect or irregularity within a crystal structure that contains an abrupt change in the arrangement of atoms. The movement of dislocations allow atoms to sli ...

of the humeral head when a person carries heavy loads. The function of abduction also means that it would help keep carried objects a safer distance away from the thighs to avoid hitting them, as during a farmer's walk. It also ensures a precise and rapid movement of the

glenohumeral joint The shoulder joint (or glenohumeral joint from Greek ''glene'', eyeball, + -''oid'', 'form of', + Latin ''humerus'', shoulder) is structurally classified as a synovial ball-and-socket joint and functionally as a diarthrosis and multiaxial joint ...

needed for hand and arm manipulation. The intermediate fibers are in the most efficient position to perform this role, though like basic abduction movements (such as lateral raise) it is assisted by simultaneous co-contraction of anterior/posterior fibers. The deltoid is responsible for elevating the arm in the scapular plane and its contraction in doing this also elevates the humeral head. To stop this compressing against the undersurface of the

the humeral head and injuring the supraspinatus tendon, there is a simultaneous contraction of some of the muscles of the

rotator cuff The rotator cuff (SITS muscles) is a group of muscles and their tendons that act to stabilize the human shoulder and allow for its extensive range of motion. Of the seven scapulohumeral muscles, four make up the rotator cuff. The four muscles a ...

: the

and subscapularis primarily perform this role. In spite of this there may be still a 1–3 mm upward movement of the head of the humerus during the first 30° to 60° of arm elevation.

Clinical significance

The most common abnormalities affecting the deltoid are tears, fatty atrophy, and

enthesopathy An enthesopathy refers to a disorder involving the attachment of a tendon or ligament to a bone. This site of attachment is known as the entheses, enthesis (pl. entheses). If the condition is known to be Inflammation, inflammatory, it can more pr ...

. Deltoid muscle tears are unusual and frequently related to traumatic shoulder dislocation or massive rotator cuff tears. Muscle atrophy may result from various causes, including aging, disuse,

denervation Denervation is any loss of nerve supply regardless of the cause. If the nerves lost to denervation are part of neural communication to an organ system or for a specific tissue function, alterations to or compromise of physiological functioning ca ...

muscular dystrophy Muscular dystrophies (MD) are a genetically and clinically heterogeneous group of rare neuromuscular diseases that cause progressive weakness and breakdown of skeletal muscles over time. The disorders differ as to which muscles are primarily affe ...

cachexia Cachexia () is a syndrome that happens when people have certain illnesses, causing muscle loss that cannot be fully reversed with improved nutrition. It is most common in diseases like cancer, Heart failure, congestive heart failure, chronic o ...

and

iatrogenic injury A medical error is a preventable adverse effect of care ("iatrogenesis"), whether or not it is evident or harmful to the patient. This might include an inaccurate or incomplete diagnosis or treatment of a disease, injury, syndrome, behavior, i ...

. Deltoidal humeral enthesopathy is an exceedingly rare condition related to mechanical stress. Conversely, deltoideal acromial enthesopathy is likely a hallmark of seronegative spondylarthropathies and its detection should probably be followed by pertinent clinical and serological investigation. The Deltoid Muscle is tested by asking the patient to abduct the arm against resistance applied with one hand, and feeling for the contracting muscle with the other hand. Site of the intramuscular injection in deltoid: The intramuscular injections are commonly given in the lower half of the deltoid to avoid injury to the axillary nerve, which winds around the surgical neck of the humerus.

Other animals

The deltoid is also found in members of the

great ape The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); '' Gorilla'' (the ...

family other than humans. The human deltoid is of similar proportionate size as the muscles of the rotator cuff in apes like the

orangutan Orangutans are great apes native to the rainforests of Indonesia and Malaysia. They are now found only in parts of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China. Classified in the genus ...

, which engage in

brachiation Brachiation (from "brachium", Latin for "arm"), or arm swinging, is a form of arboreal locomotion in which primates swing from tree limb to tree limb using only their arms. During brachiation, the body is alternately supported under each forelimb ...

and possess the muscle mass needed to support the body weight by the shoulders. In other apes, like the

common chimpanzee The chimpanzee (; ''Pan troglodytes''), also simply known as the chimp, is a species of great ape native to the forests and savannahs of tropical Africa. It has four confirmed subspecies and a fifth proposed one. When its close relative the ...

, the deltoid is much larger than in humans, weighing an average of 383.3 gram compared to 191.9 gram in humans. This reflects the need to strengthen the shoulders, particularly the rotatory cuff, in knuckle walking apes for the purpose of supporting the entire body weight. The deltoid muscle is a main component of both the

bat Bats are flying mammals of the order Chiroptera (). With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most birds, flying with their very long spread-out ...

and

pterosaur Pterosaurs are an extinct clade of flying reptiles in the order Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 million to 66 million years ago). Pterosaurs are the earli ...

wing musculature, but in crown-group birds it is strongly reduced, as they favour sternum attached muscles. Some Mesozoic flying theropods, however, had more developed deltoideus.

References

* Standring, S. (2005). Gray's Anatomy: The Anatomical Basis of Clinical Practice (39th ed.). Elsevier Churchill Livingstone. {{DEFAULTSORT:Deltoid Muscle Muscles of the upper limb Shoulder abductors Shoulder flexors Shoulder medial rotators Shoulder extensors Shoulder lateral rotators