Biceps

The biceps brachii is a prominent fusiform muscle of the anterior compartment of the arm and forms much of the visible muscular contour of the anterior upper arm. Its superficial position makes it one of the most readily observed and palpated muscles of the upper limb.

The name biceps refers to the muscle's two proximal heads, the long head and short head. These arise separately from the scapula and unite to form a common muscular belly. Distally, the muscle narrows into a strong tendon that attaches to the radial tuberosity, while the bicipital aponeurosis extends medially into the deep fascia of the forearm.

The visible shape of the biceps changes considerably with elbow position, forearm position, muscular contraction, and individual muscle development. Contraction against resistance makes the muscle belly and distal tendon particularly prominent.

Surface Location

The biceps occupies the anterior aspect of the arm between the shoulder and elbow. Its main muscle belly is superficial and can usually be seen or palpated through the skin and superficial fascia.

Proximally, the muscle lies deep to portions of the deltoid and pectoral region. Distally, its muscle belly narrows toward the cubital fossa, where the distal biceps tendon becomes an important surface landmark.

Visible Muscle Bulk

The visible bulk of the biceps occupies much of the anterior arm. When relaxed, it contributes to the rounded contour between the deltoid superiorly and the elbow inferiorly. During resisted elbow flexion, the muscle belly becomes shorter, thicker, and more prominent.

The contour reflects the underlying fusiform architecture of the muscle, with a relatively broad central belly tapering toward its tendinous attachments.

Long Head

The long head of biceps brachii originates from the supraglenoid tubercle of the scapula and adjacent superior glenoid labral region. Its tendon passes through the shoulder joint region before entering the intertubercular groove of the humerus.

Within the arm, the long head contributes predominantly to the lateral portion of the biceps muscle belly.

Short Head

The short head of biceps brachii originates from the tip of the coracoid process of the scapula together with the coracobrachialis.

It contributes predominantly to the medial portion of the biceps muscle belly and joins the long head as the muscle descends through the arm.

Proximal Attachments

Head	Proximal Attachment
Long head	Supraglenoid tubercle and adjacent superior glenoid labral region
Short head	Coracoid process of scapula

Distal Attachment

The biceps muscle belly narrows distally to form the distal biceps tendon. This tendon crosses the anterior aspect of the elbow and attaches principally to the radial tuberosity.

Because the tendon inserts onto the radius, biceps brachii can produce powerful supination of the forearm in addition to elbow flexion.

Bicipital Aponeurosis

The bicipital aponeurosis, also called the lacertus fibrosus, is a broad fibrous expansion arising from the distal biceps tendon. It passes medially and blends with the deep fascia of the forearm.

The aponeurosis contributes to the roof of the cubital fossa and separates more superficial structures from the brachial artery and median nerve lying deeper within the region.

Shape of the Biceps

Biceps brachii is classically described as a fusiform muscle. Its fibers are arranged around a relatively thick central muscle belly that tapers toward the proximal and distal tendinous regions.

This architecture contributes to the characteristic rounded prominence visible during contraction.

Relationship to the Deltoid

Superiorly, the biceps approaches the inferior border of the deltoid. The deltoid forms the rounded contour of the shoulder, while the biceps contributes to the anterior contour of the arm below it.

The transition between these muscle groups is an important feature of upper limb surface anatomy.

Relationship to Brachialis

The brachialis lies deep to biceps brachii over much of the distal half of the arm. Portions of brachialis become visible or palpable on either side of the distal biceps, particularly in individuals with well-developed musculature.

Brachialis is a powerful elbow flexor and contributes to the contour of the distal anterior arm.

Relationship to Coracobrachialis

The coracobrachialis lies in the proximal medial arm and shares its proximal attachment at the coracoid process with the short head of biceps.

It lies deeper and more medially than the prominent biceps muscle belly and is considerably less obvious on surface inspection.

Medial and Lateral Bicipital Grooves

The margins of the biceps create longitudinal surface depressions along the arm known as the medial and lateral bicipital grooves.

These grooves correspond to intervals between the biceps and adjacent muscles and provide useful surface landmarks for deeper neurovascular structures.

Medial Bicipital Groove

The medial border of the biceps forms a groove between the muscle and the medial structures of the arm. The brachial artery can be palpated along the medial aspect of the biceps, particularly in the distal arm.

The median nerve is also closely associated with the brachial artery as the structures descend toward the cubital fossa.

Lateral Bicipital Groove

The lateral border of the biceps forms a less pronounced groove separating the muscle from neighboring structures. The cephalic vein ascends superficially along the lateral side of the arm and enters the deltopectoral groove superiorly.

Cubital Fossa Relationship

The distal biceps tendon enters the cubital fossa, the triangular region on the anterior aspect of the elbow. The tendon is an important landmark for identifying structures within the fossa.

From lateral to medial, major structures in the central cubital region include the biceps tendon, brachial artery, and median nerve, although the complete anatomy of the fossa includes additional structures and boundaries.

Distal Biceps Tendon

The distal biceps tendon can be palpated in the cubital fossa when the elbow is flexed against resistance, particularly with the forearm supinated.

It feels like a firm cord extending from the distal muscle belly toward its attachment on the radial tuberosity.

Palpation of the Biceps

The biceps is easily palpated by asking the individual to flex the elbow against resistance. Supination of the forearm increases recruitment of biceps brachii and helps distinguish it from other elbow flexors.

The examiner can palpate the central muscle belly and then follow it distally toward the biceps tendon in the cubital fossa.

Palpation Sequence

1. Position the arm so the anterior upper arm is accessible.
2. Ask for elbow flexion against resistance.
3. Palpate the prominent central biceps muscle belly.
4. Ask the individual to supinate the forearm against resistance to increase biceps activation.
5. Follow the muscle distally toward the cubital fossa.
6. Identify the firm distal biceps tendon.
7. Palpate the medial and lateral margins of the muscle to appreciate its relationship with neighboring structures.

Effect of Elbow Flexion

During elbow flexion, the biceps shortens and its central muscle belly becomes more prominent. This change is particularly obvious when flexion occurs against resistance.

In full extension, the muscle becomes elongated and its visible prominence decreases.

Effect of Forearm Position

Forearm position substantially influences the mechanical action and surface appearance of biceps brachii. The muscle is a particularly effective elbow flexor when the forearm is supinated and a powerful supinator when the forearm begins in pronation.

Resisted supination therefore provides an effective method for making the muscle and its distal tendon prominent during surface examination.

Elbow Flexion

Biceps brachii contributes to flexion of the elbow. Its effectiveness varies with forearm position because the distal tendon attaches to the radius.

Brachialis remains a major flexor regardless of forearm rotation, while biceps becomes especially effective when the forearm is supinated.

Forearm Supination

Biceps brachii is a powerful supinator of the forearm. Contraction pulls on the radial tuberosity, rotating the radius so that the palm turns anteriorly in the anatomical position or superiorly when the elbow is flexed.

Its supination action is particularly powerful when the elbow is flexed.

Shoulder Actions

Because both heads originate from the scapula and cross the shoulder region, biceps brachii can contribute to movements and stabilization at the glenohumeral joint.

Its role at the shoulder is less dominant than its actions at the elbow and radioulnar joints.

Actions of Biceps Brachii

Action	Functional Role
Forearm supination	Powerful rotation of radius into supinated position
Elbow flexion	Flexes forearm at elbow, especially effectively with forearm supinated
Shoulder movement	Can assist movement and stabilization at glenohumeral joint

Innervation

Biceps brachii is innervated by the musculocutaneous nerve, primarily through fibers derived from the C5 and C6 spinal nerve levels.

The musculocutaneous nerve enters the anterior compartment of the arm and supplies biceps brachii, brachialis, and coracobrachialis.

Blood Supply

The biceps receives arterial blood primarily through muscular branches of the brachial artery, with contributions from neighboring arterial branches.

The brachial artery travels along the medial aspect of the biceps before entering the cubital fossa.

Brachial Artery as a Surface Relationship

The brachial pulse can be palpated along the medial side of the biceps, particularly in the distal arm and cubital fossa.

The close relationship between the artery and the biceps makes the muscle an important surface landmark during vascular examination.

Biceps Reflex

The biceps tendon reflex is commonly assessed by placing the examiner's finger over the biceps tendon in the cubital region and striking the finger with a reflex hammer.

The response involves contraction of biceps brachii and elbow flexion and is used clinically in assessment of the musculocutaneous nerve and spinal cord segments associated predominantly with C5 and C6.

Long Head Tendon at the Shoulder

The tendon of the long head passes from its proximal attachment through the shoulder joint region and enters the intertubercular groove of the humerus.

Although the tendon is deep proximally, its anatomical course is important when examining anterior shoulder pain associated with the bicipital region.

Intertubercular Groove

The intertubercular groove lies between the greater and lesser tubercles of the humerus. The long head of the biceps tendon travels within this groove as it descends from the shoulder toward the muscle belly.

The groove is covered by overlying soft tissues and is less directly accessible than the superficial muscle belly in the arm.

Proximal Biceps Tendon Pathology

The long head tendon can develop degenerative, inflammatory, or traumatic abnormalities. Because of its relationship with the shoulder joint and rotator cuff, pathology of the long head tendon can occur together with other shoulder disorders.

Tenderness may be localized to the anterior shoulder near the course of the intertubercular groove.

Long Head Biceps Rupture

Rupture of the long head tendon can alter the normal contour of the biceps. The muscle belly may retract distally and become unusually prominent in the lower portion of the arm during contraction.

This characteristic contour is commonly described as a Popeye deformity.

Popeye Deformity

A Popeye deformity results from displacement of the biceps muscle belly after disruption of a proximal tendon, most commonly the long head tendon.

The visible abnormality demonstrates how tendon integrity influences the normal position and shape of superficial muscle bulk.

Distal Biceps Tendon Rupture

Rupture of the distal biceps tendon disrupts the connection between the muscle and radial tuberosity. This can alter the contour of the distal arm and produce weakness, particularly during resisted forearm supination.

The distal tendon may no longer be palpable normally within the cubital fossa.

Hook Test

The hook test is a clinical examination maneuver used to assess the continuity of the distal biceps tendon. With the elbow flexed and forearm supinated, the examiner attempts to hook a finger beneath the intact distal tendon from the lateral side.

Failure to identify the expected tendon can raise suspicion of complete distal tendon rupture, although clinical findings are interpreted together with the remainder of the examination and appropriate imaging when required.

Biceps Tendinopathy

Tendinopathy can involve the proximal long head tendon or, less commonly, the distal biceps tendon. Symptoms may occur near the shoulder or cubital region depending on the affected portion.

Surface localization helps distinguish tendon-related symptoms from pathology involving neighboring muscles, joints, nerves, or other soft tissues.

Biceps and Brachialis

Feature	Biceps Brachii	Brachialis
Position	Superficial anterior arm	Deep to biceps
Distal attachment	Radius	Ulna
Elbow flexion	Yes	Yes, major pure flexor
Supination	Powerful action	No major role
Surface visibility	Highly prominent	Partly visible near distal margins of biceps

Biceps and Triceps Surface Relationship

The biceps forms the major visible muscle bulk of the anterior arm, while the triceps brachii forms most of the muscular bulk of the posterior arm.

The intermuscular septa and humerus separate the anterior and posterior muscular compartments, although their contours can be appreciated together during surface examination of the arm.

Changes with Muscular Contraction

During contraction, the biceps muscle belly becomes shorter and increases in thickness. This produces the familiar rounded prominence on the anterior arm.

The magnitude of visible change depends on muscle size, subcutaneous tissue thickness, joint position, contraction intensity, and individual anatomy.

Changes with Muscle Development

Muscular hypertrophy can substantially increase the visible prominence of the biceps. However, the exact external shape of the muscle is also influenced by the relative lengths of the muscle belly and tendons and by individual anatomical variation.

Consequently, individuals with similar muscle strength or muscle volume may have different visible biceps contours.

Subcutaneous Tissue

The degree to which the biceps is visible at rest depends partly on the thickness and distribution of overlying subcutaneous tissue. The muscle may remain readily palpable even when its margins are not sharply visible.

Surface appearance therefore does not provide a direct measurement of muscle strength or functional capacity.

Important Surface Relationships

Surface Feature	Anatomical Relationship
Central anterior arm bulk	Biceps brachii muscle belly
Medial biceps border	Important reference for brachial artery
Distal biceps tendon	Passes through cubital fossa toward radial tuberosity
Bicipital aponeurosis	Extends medially into forearm fascia
Proximal lateral portion	Predominantly long head contribution
Proximal medial portion	Predominantly short head contribution

Clinical Importance of Biceps Surface Anatomy

The superficial position of biceps brachii makes it useful for assessing muscle contraction, contour, symmetry, tendon integrity, and neurological function. Comparison of the two arms can reveal differences in muscle bulk or changes associated with injury.

The muscle also serves as an important landmark for the brachial artery, cubital fossa, distal biceps tendon, and surrounding structures. Changes in its normal contour may provide evidence of proximal or distal tendon disruption.

Functional Importance

The biceps is one of the most recognizable examples of visible muscle bulk in surface anatomy. Its superficial fusiform belly defines much of the anterior contour of the upper arm and becomes particularly prominent during resisted elbow flexion and forearm supination.

Its anatomy also demonstrates the relationship between visible muscle shape and deeper musculoskeletal structures. The two proximal heads connect the muscle to the scapula, the distal tendon transfers force to the radius, and the bicipital aponeurosis distributes connective tissue into the forearm fascia.

Understanding the surface anatomy of the biceps is fundamental to the study of upper limb surface anatomy, muscle palpation, elbow flexion, forearm supination, cubital fossa anatomy, brachial artery localization, tendon examination, and biceps tendon injuries.