Biceps brachii muscle
Encyclopedia
In human anatomy
, the biceps brachii, or simply biceps in common parlance, is, as the name implies, a two-headed muscle
located on the upper arm. Both heads arise on the scapula
and join to form a single muscle belly which is attached to the upper forearm. While the biceps crosses both the shoulder
and elbow joints, its main function is at the latter where it flexes the elbow and supinates
the forearm. Both these movements are used when opening a bottle with a corkscrew: first biceps unscrews the cork (supination), then it pulls the cork out (flexion).
form of the Latin adjective
biceps is bicipites, a form not in general English use. Instead, biceps is used in both singular
and plural (i.e., when referring to both arms).
The English form , attested from 1939, is a back formation derived from interpreting the s of biceps as the English plural
marker -s. While common even in professional contexts, it is often considered incorrect.
The biceps brachii muscle is the one that gave all muscles their name: it comes from the Latin
musculus, "little mouse", because the appearance of the flexed biceps resembles the back of a mouse. The same phenomenon occurred in Greek
, in which μῦς, mȳs, means both "mouse" and "muscle".
. The long head originates on the supraglenoid tubercle
just above the shoulder joint from where its tendon
passes down along the intertubercular groove
of the humerus
into the joint capsule
of the shoulder joint.
When the humerus is in motion, the tendon of the long head is held firmly in place in the intertubercular groove by the greater
and lesser tubercle
s and the overlying transverse humeral ligament
. During the motion from external to internal rotation, the tendon is forced medially against the lesser tubercle and superiorly against the transverse ligament.
Both heads join on the middle of the humerus, usually near the insertion of the deltoid
, to form a common muscle belly. Distally (towards the fingers), biceps ends in two tendons: the stronger attaches to (inserts into) the radial tuberosity
on the radius
, while the other, the bicipital aponeurosis
, radiates into the ulnar part of the antebrachial fascia
.
Two additional muscles lie underneath the biceps brachii. These are the coracobrachialis muscle
, which like the biceps attaches to the coracoid process of the scapula, and the brachialis muscle
which connects to the ulna
and along the mid-shaft of the humerus
.
in 10% of cases (normal variation) — most commonly originating near the insertion of the coracobrachialis and joining the short head — but four, five, and even seven supernumerary
heads have been reported in rare cases.
The distal biceps tendons are completely separated in 40% and bifurcated
in 25% of cases.
together with coracobrachialis and brachialis; like the latter, from fibers of the fifth and sixth cervical nerves
.
These joints and the associated actions are listed as follows in order of importance:
and resistance training
. An example of a well known biceps exercise is the simple biceps curl
.
s, the radial bicipital tuberosities were larger than in modern humans
, which suggests they were probably able to use their biceps for supination over a wider range of pronation-supination.
It is possible that they relied more on their biceps for forceful supination without the assistance of the supinator muscle
like in modern humans, and thus that they used a different movement when throwing.
In the horse, the biceps' function is to extend the shoulder and flex the elbow. It is composed of two short-fibred heads separated longitudinally by a thick internal tendon which stretches from the origin on the supraglenoid tubercle to the insertion on the medial radial tuberosity. This tendon is capable to withstand very large forces when the biceps is stretched. From this internal tendon a strip of tendon, the lacertus fibrosus, connects the muscle with the extensor carpi radialis
-- an important feature in the horse's stay apparatus (through which the horse can rest and sleep whilst standing.)
De Maeseneer described in the publicly accessible paper the specific tendon imaging in the following way: “The tendon of the long head of the biceps muscle attaches to the antero-superior aspect of the glenoid rim. The attachment of the biceps tendon may demonstrate four components, including fibers that attach to the antero-superior labrum, the postero-superior labrum, the supraglenoid tubercle, and the base of the coracoid process. From its site of attachment, the biceps tendon courses laterally and exits the gleno-humeral joint through the intertubercular groove, where it is secured by the transverse ligament. The labral-bicipital complex is well visualized on transverse CT or MR arthrograms as well as on coronal MR arthrograms and reconstructed images from coronal CT arthrograms.”
At the ingress through the sulcus intertubercularis the so called pulley system stabilizes the tendon. The pulley system is formed by the coracohumeral and superior glenohumeral ligaments. The intraarticular part of the long head of the biceps brachii muscle accounts to the superior stabilization of the humerus head. In the last few years, injuries of the biceps tendon anchor have been considered as a reason for chronic shoulder pain. Especially in overhead athletes.
In 8 out of 10 cases the dominant arm is affected. A predisposition for tendon ruptures in general is a degeneration due to overuse or steroid taking. Predispositive are also systemic diseases like hyperparathyroidism, diabetes mellitus, gout or non-systemic inflammatory thickening of the biceps tendon or bone hypertrophy at the radial tuberosity due to the impingement. Most tendon injuries are located at the tuberositas radialis, which could be explained with a found hypovascularisation of the tendon 1cm more proximally.
Radiological signs for a complete rupture:
Ultrasonographic findings on longitudinal and transversal plane, ventral humero-radial in supination: Hypoechoic hematoma at the insertion area of the tuberositas radii, instead of a parallel echogenic insertion. Changes of the contour, retraction of the M. biceps brachii and hemarthrosis.
Sagittal sequences are useful for assessing the degree of tendon retraction. A bone marrow edema in the tuberositas radialis and fluid in the bursa bicipito-radialis indicate a partial rupture and facilitate the discrimination to a tendinosis. An isolated bursitis is often clinically not clearly distinguishable from a biceps tendinosis. A biceps tendinosis does affect the tendon’s biomechanical tensile strength negatively. Hematoma or large effusion in the bursa could cause nerve compression of the N. medianus, N. radialis or Nn. interosseus posteriores.
A conservative treatment leads to a loss of 30-40% strength in flexion and supination. It is therefore recommended to surgically re-fix the tendon to the tuberositas radialis within the first 2 weeks after the trauma, especially in physically active patients with high expectations. Within the first 2 weeks the muscle gets neither scarred nor retracted.
Human anatomy
Human anatomy is primarily the scientific study of the morphology of the human body. Anatomy is subdivided into gross anatomy and microscopic anatomy. Gross anatomy is the study of anatomical structures that can be seen by the naked eye...
, the biceps brachii, or simply biceps in common parlance, is, as the name implies, a two-headed muscle
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...
located on the upper arm. Both heads arise on the scapula
Scapula
In anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
and join to form a single muscle belly which is attached to the upper forearm. While the biceps crosses both the shoulder
Shoulder
The human shoulder is made up of three bones: the clavicle , the scapula , and the humerus as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder make up the shoulder joints. The major joint of the shoulder is the glenohumeral joint, which...
and elbow joints, its main function is at the latter where it flexes the elbow and supinates
Supination
Supination is a position of either the forearm or foot; in the forearm when the palm faces anteriorly, or faces up . Supination in the foot occurs when a person appears "bow-legged" with their weight supported primarily on the anterior of their feet.The hand is supine in the anatomical position...
the forearm. Both these movements are used when opening a bottle with a corkscrew: first biceps unscrews the cork (supination), then it pulls the cork out (flexion).
Terminology
The term biceps brachii is a Latin phrase meaning "two-headed [muscle] of the arm", in reference to the fact that the muscle consists of two bundles of muscle, each with its own origin, sharing a common insertion point near the elbow joint. The proper pluralPlural
In linguistics, plurality or [a] plural is a concept of quantity representing a value of more-than-one. Typically applied to nouns, a plural word or marker is used to distinguish a value other than the default quantity of a noun, which is typically one...
form of the Latin adjective
Adjective
In grammar, an adjective is a 'describing' word; the main syntactic role of which is to qualify a noun or noun phrase, giving more information about the object signified....
biceps is bicipites, a form not in general English use. Instead, biceps is used in both singular
Grammatical number
In linguistics, grammatical number is a grammatical category of nouns, pronouns, and adjective and verb agreement that expresses count distinctions ....
and plural (i.e., when referring to both arms).
The English form , attested from 1939, is a back formation derived from interpreting the s of biceps as the English plural
English plural
In the English language, nouns are inflected for grammatical number —that is, singular or plural. This article discusses the variety of ways in which English plurals are formed for nouns...
marker -s. While common even in professional contexts, it is often considered incorrect.
The biceps brachii muscle is the one that gave all muscles their name: it comes from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
musculus, "little mouse", because the appearance of the flexed biceps resembles the back of a mouse. The same phenomenon occurred in Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
, in which μῦς, mȳs, means both "mouse" and "muscle".
Origin and insertion
Proximally (towards the body), the short head of the biceps attaches to (originates from) the coracoid process at the top of the scapulaScapula
In anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
. The long head originates on the supraglenoid tubercle
Supraglenoid tubercle
The supraglenoid tubercle is a region of the scapula to which the long head of the biceps brachii muscle attaches. It is a small, rough projection just superior to the Glenoid cavity near the base of the coracoid process...
just above the shoulder joint from where its tendon
Tendon
A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...
passes down along the intertubercular groove
Intertubercular groove
The tubercles of the humerus are separated from each other by a deep groove, the intertubercular groove , which lodges the long tendon of the Biceps brachii and transmits a branch of the anterior humeral circumflex artery to the shoulder-joint.It runs obliquely downward, and ends near the junction...
of the humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
into the joint capsule
Joint capsule
An articular capsule is an envelope surrounding a synovial joint.-Layers:Each capsule consists of two layers:* an outer layer composed of avascular white fibrous tissue...
of the shoulder joint.
When the humerus is in motion, the tendon of the long head is held firmly in place in the intertubercular groove by the greater
Greater tubercle
The greater tubercle of the humerus is situated lateral to the head of the humerus and posteriolateral to the lesser tubercle.Its upper surface is rounded and marked by three flat impressions....
and lesser tubercle
Lesser tubercle
The lesser tubercle of the humerus, although smaller, is more prominent than the greater tubercle: it is situated in front, and is directed medially and anteriorly....
s and the overlying transverse humeral ligament
Transverse humeral ligament
The transverse humeral ligament is a broad band passing from the lesser to the greater tubercle of the humerus, and always limited to that portion of the bone which lies above the epiphysial line....
. During the motion from external to internal rotation, the tendon is forced medially against the lesser tubercle and superiorly against the transverse ligament.
Both heads join on the middle of the humerus, usually near the insertion of the deltoid
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...
, to form a common muscle belly. Distally (towards the fingers), biceps ends in two tendons: the stronger attaches to (inserts into) the radial tuberosity
Radial tuberosity
Beneath the neck of the radius, on the medial side, is an eminence, the radial tuberosity; its surface is divided into:* a posterior, rough portion, for the insertion of the tendon of the biceps brachii....
on the radius
Radius (bone)
The radius is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna, which exceeds it in length and size. It is a long bone, prism-shaped and slightly curved longitudinally...
, while the other, the bicipital aponeurosis
Bicipital aponeurosis
The bicipital aponeurosis is a broad aponeurosis of the biceps brachii which is located in the cubital fossa of the elbow and separates superficial from deep structures in much of the fossa....
, radiates into the ulnar part of the antebrachial fascia
Antebrachial fascia
The antebrachial fascia continuous above with the brachial fascia, is a dense, membranous investment, which forms a general sheath for the muscles in this region; it is attached, behind, to the olecranon and dorsal border of the ulna, and gives off from its deep surface numerous intermuscular...
.
Two additional muscles lie underneath the biceps brachii. These are the coracobrachialis muscle
Coracobrachialis muscle
The Coracobrachialis is the smallest of the three muscles that attach to the coracoid process of the scapula. It is situated at the upper and medial part of the arm....
, which like the biceps attaches to the coracoid process of the scapula, and the brachialis muscle
Brachialis muscle
The brachialis is a muscle in the upper arm that flexes the elbow joint. It lies deeper than the biceps brachii, and is a synergist that assists the biceps brachii in flexing at the elbow...
which connects to the ulna
Ulna
The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...
and along the mid-shaft of the humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
.
Variation
Traditionally described as a two-headed muscle, biceps brachii is one of the most variable muscles of the human body and has a third head arising from the humerusHumerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
in 10% of cases (normal variation) — most commonly originating near the insertion of the coracobrachialis and joining the short head — but four, five, and even seven supernumerary
Supernumerary body part
Supernumerary body parts are most commonly a congenital disorder involving the growth of an additional part of the body and a deviation from the body plan. Body parts may be easily visible or hidden away, such as internal organs....
heads have been reported in rare cases.
The distal biceps tendons are completely separated in 40% and bifurcated
Bifurcation
Bifurcation means the splitting of a main body into two parts.Bifurcation or Bifurcated may refer to:*Bifurcation , the division of issues in a trial for example the division of a page into two parts....
in 25% of cases.
Innervation
Biceps brachii is innervated by the musculocutaneous nerveMusculocutaneous nerve
The musculocutaneous nerve arises from the lateral cord of the brachial plexus, opposite the lower border of the Pectoralis major, its fibers being derived from C5, C6 and C7.-Path:...
together with coracobrachialis and brachialis; like the latter, from fibers of the fifth and sixth cervical nerves
Cervical nerves
The cervical nerves are the spinal nerves from the cervical vertebrae.Although there are seven cervical vertebrae , there are eight cervical nerves . All nerves except C8 emerge above their corresponding vertebrae, while the C8 nerve emerges below the C7 vertebra...
.
Functions
The biceps is tri-articulate, meaning that it works across three joints. The most important of these functions is to supinate the forearm and flex the elbow.These joints and the associated actions are listed as follows in order of importance:
- Proximal radioulnar joint (upper forearm) – Contrary to popular belief, the biceps brachii is not the most powerful flexor of the forearm, a role which actually belongs to the deeper brachialis muscle. The biceps brachii functions primarily as a powerful supinator of the forearm (turns the palm upwards). This action, which is aided by the supinator muscle, requires the elbow to be at least partially flexed. If the elbow, or humeroulnar jointHumeroulnar jointThe humeroulnar joint, is part of the elbow-joint or the Olecron Joint, between the ulna and humerus bones is the simple hinge-joint, which allows for movements of flexion, extension and circumduction...
, is fully extended, supination is then primarily carried out by the supinator muscle. - Humeroulnar jointHumeroulnar jointThe humeroulnar joint, is part of the elbow-joint or the Olecron Joint, between the ulna and humerus bones is the simple hinge-joint, which allows for movements of flexion, extension and circumduction...
(elbow) – The biceps brachii also functions as an important flexor of the forearm, particularly when the forearm is supinated. Functionally, this action is performed when lifting an object, such as a bag of groceries or when performing a biceps curlBiceps curlThe biceps curl is any of a number of weight training exercises that target the biceps brachii muscle in order to develop one or more of the following attributes:*size*definition*strength*endurance*power...
. When the forearm is in pronationPronationIn anatomy, pronation is a rotational movement of the forearm at the radioulnar joint, or of the foot at the subtalar and talocalcaneonavicular joints. For the forearm, when standing in the anatomical position, pronation will move the palm of the hand from an anterior-facing position to a...
(the palm faces the ground), the brachialis, brachioradialisBrachioradialisBrachioradialis is a muscle of the forearm that acts to flex the forearm at the elbow. It is also capable of both pronation and supination, depending on the position of the forearm...
, and supinator function to flex the forearm, with minimal contribution from the biceps brachii. - Glenohumeral jointGlenohumeral jointThe glenohumeral joint, or shoulder joint, is a multiaxial synovial ball and socket joint and involves articulation between the glenoid fossa of the scapula and the head of the humerus...
(shoulder) – Several weaker functions occur at the glenohumeral, or shoulder, joint. The biceps brachii weakly assists in forward flexion of the shoulder joint (bringing the arm forward and upwards). It may also contribute to abductionAbduction (kinesiology)Abduction, in functional anatomy, is a movement which draws a limb away from the median plane of the body. It is thus opposed to adduction.-Upper limb:* of arm at shoulder ** Supraspinatus** Deltoid* of hand at wrist...
(bringing the arm out to the side) when the arm is externally (or laterally) rotated. The short head of the biceps brachii also assists with horizontal adductionAdductionAdduction 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...
(bringing the arm across the body) when the arm is internally (or medially) rotated. Finally, the long head of the biceps brachii, due to its attachment to the scapulaScapulaIn anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
(or shoulder blade), assists with stabilization of the shoulder joint when a heavy weight is carried in the arm.
Training
The biceps can be strengthened using weightWeight training
Weight training is a common type of strength training for developing the strength and size of skeletal muscles. It uses the weight force of gravity to oppose the force generated by muscle through concentric or eccentric contraction...
and resistance training
Resistance training
Resistance training has two different meanings. A broader meaning that refers to any training that uses a resistance to the force of muscular contraction , and elastic or hydraulic resistance, which refers to a specific type of strength training that uses elastic or hydraulic tension to provide...
. An example of a well known biceps exercise is the simple biceps curl
Biceps curl
The biceps curl is any of a number of weight training exercises that target the biceps brachii muscle in order to develop one or more of the following attributes:*size*definition*strength*endurance*power...
.
Evolutionary variation
In NeanderthalNeanderthal
The Neanderthal is an extinct member of the Homo genus known from Pleistocene specimens found in Europe and parts of western and central Asia...
s, the radial bicipital tuberosities were larger than in modern humans
Anatomically modern humans
The term anatomically modern humans in paleoanthropology refers to early individuals of Homo sapiens with an appearance consistent with the range of phenotypes in modern humans....
, which suggests they were probably able to use their biceps for supination over a wider range of pronation-supination.
It is possible that they relied more on their biceps for forceful supination without the assistance of the supinator muscle
Supinator muscle
In human anatomy, the supinator is a broad muscle in the posterior compartment of the forearm, curved around the upper third of the radius. Its function is to supinate the forearm.-Terminology:...
like in modern humans, and thus that they used a different movement when throwing.
In the horse, the biceps' function is to extend the shoulder and flex the elbow. It is composed of two short-fibred heads separated longitudinally by a thick internal tendon which stretches from the origin on the supraglenoid tubercle to the insertion on the medial radial tuberosity. This tendon is capable to withstand very large forces when the biceps is stretched. From this internal tendon a strip of tendon, the lacertus fibrosus, connects the muscle with the extensor carpi radialis
Extensor carpi radialis
Extensor carpi radialis can refer to:* Extensor carpi radialis brevis muscle* Extensor carpi radialis longus muscle...
-- an important feature in the horse's stay apparatus (through which the horse can rest and sleep whilst standing.)
Imaging of the long head tendon
The conventional radiography can illustrate the bony channel for the long head tendon. This bicipital sulcus is delineated by the major and minor humeral tuberosities. Fractures with subsequent deformation of the sulcus may lead to painful internal or external rotation. A conventional radiography can clearly depict these deformations.De Maeseneer described in the publicly accessible paper the specific tendon imaging in the following way: “The tendon of the long head of the biceps muscle attaches to the antero-superior aspect of the glenoid rim. The attachment of the biceps tendon may demonstrate four components, including fibers that attach to the antero-superior labrum, the postero-superior labrum, the supraglenoid tubercle, and the base of the coracoid process. From its site of attachment, the biceps tendon courses laterally and exits the gleno-humeral joint through the intertubercular groove, where it is secured by the transverse ligament. The labral-bicipital complex is well visualized on transverse CT or MR arthrograms as well as on coronal MR arthrograms and reconstructed images from coronal CT arthrograms.”
At the ingress through the sulcus intertubercularis the so called pulley system stabilizes the tendon. The pulley system is formed by the coracohumeral and superior glenohumeral ligaments. The intraarticular part of the long head of the biceps brachii muscle accounts to the superior stabilization of the humerus head. In the last few years, injuries of the biceps tendon anchor have been considered as a reason for chronic shoulder pain. Especially in overhead athletes.
Imaging of the distal insertion
Only about 5% of biceps ruptures are distal. They only occur in men and usually around the age of 40 to 60 years, typically after a sudden extension force at a 90° flexed arm in supination.In 8 out of 10 cases the dominant arm is affected. A predisposition for tendon ruptures in general is a degeneration due to overuse or steroid taking. Predispositive are also systemic diseases like hyperparathyroidism, diabetes mellitus, gout or non-systemic inflammatory thickening of the biceps tendon or bone hypertrophy at the radial tuberosity due to the impingement. Most tendon injuries are located at the tuberositas radialis, which could be explained with a found hypovascularisation of the tendon 1cm more proximally.
Radiological signs for a complete rupture:
- The distal biceps tendon is missing.
- Tendon retraction, if combined with a rupture of the aponeurosis bicipitalis.
- A diffusely circumscribed mass in the distal biceps tendon, which is the correlate of a hematoma or an extensive soft tissue swelling in the fossa antecubitalis.
Ultrasonography
With sufficient experience of the examiner, which is an essential factor for a successful ultrasonographic assessment in general, the ultrasound is the method of choice for distal biceps tendon ruptures. This makes an expensive MR imaging mostly unnecessary.Ultrasonographic findings on longitudinal and transversal plane, ventral humero-radial in supination: Hypoechoic hematoma at the insertion area of the tuberositas radii, instead of a parallel echogenic insertion. Changes of the contour, retraction of the M. biceps brachii and hemarthrosis.
MRI
Axial MRI sequences are necessary to determine the exact degree of tendon injury. They can show a proximally thickened and signal increased distal biceps tendon including a surrounding irritative tissue reaction. More distal the tendon profile is not depictable, because it is completely detached from the osseous attachment.Sagittal sequences are useful for assessing the degree of tendon retraction. A bone marrow edema in the tuberositas radialis and fluid in the bursa bicipito-radialis indicate a partial rupture and facilitate the discrimination to a tendinosis. An isolated bursitis is often clinically not clearly distinguishable from a biceps tendinosis. A biceps tendinosis does affect the tendon’s biomechanical tensile strength negatively. Hematoma or large effusion in the bursa could cause nerve compression of the N. medianus, N. radialis or Nn. interosseus posteriores.
A conservative treatment leads to a loss of 30-40% strength in flexion and supination. It is therefore recommended to surgically re-fix the tendon to the tuberositas radialis within the first 2 weeks after the trauma, especially in physically active patients with high expectations. Within the first 2 weeks the muscle gets neither scarred nor retracted.