Position, Attachments, Contractions and Actions of Upper-Limb Muscles
Upper-limb muscles are arranged to stabilise the shoulder, move the arm, position the forearm and control the wrist and fingers. A muscle’s position, attachments, fibre direction, nerve supply and line of pull determine its action. Physiotherapy assessment adds the context: a muscle may act concentrically, eccentrically or isometrically depending on the task.
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How to study every muscle
For each muscle, learn P-A-I-N-A-C: Position/compartment, proximal Attachment, distal Insertion, Nerve, primary Action and the Contraction used in a real task. “Origin” and “insertion” are useful study labels, but during a closed-chain exercise either attachment may be relatively fixed.
Learning outcomes
- Locate the major muscles of the pectoral girdle, shoulder, arm, forearm and hand.
- State their proximal and distal attachments, innervation and principal actions.
- Distinguish concentric, eccentric and isometric contractions in functional tasks.
- Relate muscle architecture and line of pull to posture, movement, weakness and compensation.
- Apply muscle anatomy to testing, exercise selection, motor control and daily activities.
1. Contraction principles
| Contraction | What happens | Upper-limb example |
|---|
| Concentric | Muscle tension exceeds external load and the muscle shortens. | Biceps shortens to lift a cup toward the mouth. |
| Eccentric | Muscle remains active while lengthening under load. | Triceps controls elbow flexion as a person lowers a cup. |
| Isometric | Tension develops with little visible change in muscle length or joint angle. | Rotator cuff holds the humeral head centred while the arm is supported. |
| Isokinetic | Movement occurs at a controlled angular velocity with specialised equipment. | Laboratory or clinic dynamometer testing of elbow or shoulder strength. |
Muscle force depends on recruitment, firing frequency, length–tension relationship, contraction velocity, moment arm, fatigue, pain and the external load. A weak movement may reflect muscle injury, nerve lesion, pain inhibition, poor leverage or a joint restriction rather than a primary muscle problem.
2. Muscles of the pectoral girdle
| Muscle | Position and attachments | Innervation | Main actions |
|---|
| Trapezius | Superficial posterior neck/back; proximal: external occipital protuberance, nuchal ligament and C7–T12 spines; distal: lateral clavicle, acromion and scapular spine. | Spinal accessory nerve (XI) motor; C3–4 proprioception. | Upper fibres elevate, lower fibres depress, middle fibres retract; upper/lower fibres upwardly rotate scapula; stabilises the girdle. |
| Levator scapulae | Posterolateral neck; transverse processes C1–4 to superior medial border of scapula. | Dorsal scapular nerve and C3–4. | Elevates and downwardly rotates scapula; assists ipsilateral neck flexion. |
| Rhomboid minor | Deep to trapezius; C7–T1 spines to medial border at root of scapular spine. | Dorsal scapular nerve. | Retracts, downwardly rotates and fixes scapula to thorax. |
| Rhomboid major | T2–T5 spines to medial border from scapular spine to inferior angle. | Dorsal scapular nerve. | Retracts, downwardly rotates and stabilises scapula. |
| Serratus anterior | Superolateral thorax; ribs 1–8/9 to anterior surface of medial border and inferior angle. | Long thoracic nerve (C5–7). | Protracts and upwardly rotates scapula; holds it against thorax; lower fibres assist depression. |
| Pectoralis minor | Deep anterior chest; ribs 3–5 to coracoid process. | Medial pectoral nerve. | Depresses/protracts and downwardly rotates scapula; elevates ribs when scapula is fixed. |
| Subclavius | First rib/costal cartilage to inferior middle clavicle. | Nerve to subclavius. | Anchors and depresses clavicle; protects the SC region. |
3. Muscles crossing the shoulder
| Muscle | Proximal attachment | Distal attachment | Nerve | Principal action |
|---|
| Pectoralis major | Medial clavicle, sternum and upper costal cartilages. | Lateral lip of intertubercular sulcus. | Lateral and medial pectoral nerves. | Adducts and internally rotates arm; clavicular head flexes; sternocostal head extends a flexed arm. |
| Latissimus dorsi | Lower thoracic spines, thoracolumbar fascia, iliac crest and lower ribs. | Floor of intertubercular sulcus. | Thoracodorsal nerve. | Extends, adducts and internally rotates arm; assists climbing and pushing. |
| Deltoid | Lateral clavicle, acromion and scapular spine. | Deltoid tuberosity of humerus. | Axillary nerve. | Middle fibres abduct; anterior fibres flex/internal rotate; posterior fibres extend/external rotate. |
| Teres major | Posterior inferior angle/lateral border of scapula. | Medial lip of intertubercular sulcus. | Lower subscapular nerve. | Adducts, extends and internally rotates arm. |
| Coracobrachialis | Coracoid process. | Middle medial humeral shaft. | Musculocutaneous nerve. | Flexes and adducts arm; resists shoulder dislocation. |
| Long head of biceps | Supraglenoid tubercle and superior labrum. | Radial tuberosity and bicipital aponeurosis. | Musculocutaneous nerve. | Flexes elbow/supinates forearm; assists shoulder flexion and stability. |
4. Rotator cuff and shoulder stabilisers
| Muscle | Attachment | Nerve | Action and testing idea |
|---|
| Supraspinatus | Supraspinous fossa to superior facet of greater tubercle. | Suprascapular nerve (C5–6). | Initiates abduction and compresses the humeral head; assess with resisted abduction/scaption. |
| Infraspinatus | Infraspinous fossa to middle facet of greater tubercle. | Suprascapular nerve (C5–6). | External rotation and posterior stability. |
| Teres minor | Lateral scapular border to inferior facet of greater tubercle. | Axillary nerve (C5–6). | External rotation and adduction; assess with resisted external rotation. |
| Subscapularis | Subscapular fossa to lesser tubercle. | Upper/lower subscapular nerves. | Internal rotation and anterior stability. |
| Long head of triceps | Infraglenoid tubercle to olecranon. | Radial nerve. | Extends/adducts shoulder and extends elbow. |
Rotator-cuff muscles do not merely produce rotation; they centre the humeral head while larger muscles generate torque. Poor scapular control, fatigue, pain or altered thoracic posture can increase subacromial loading.
5. Muscles of the arm
5.1 Anterior compartment
| Muscle | Attachments | Nerve | Action |
|---|
| Biceps brachii | Long head: supraglenoid tubercle; short head: coracoid; both to radial tuberosity/aponeurosis. | Musculocutaneous. | Powerful supination and elbow flexion; assists shoulder flexion. |
| Brachialis | Distal anterior humerus to ulnar tuberosity/coronoid. | Musculocutaneous, with radial contribution. | Primary elbow flexor in all forearm positions. |
| Coracobrachialis | Coracoid to middle medial humerus. | Musculocutaneous. | Flexes/adducts shoulder and stabilises the humeral head. |
5.2 Posterior compartment
| Muscle | Attachments | Nerve | Action |
|---|
| Triceps brachii | Long: infraglenoid tubercle; lateral: posterior humerus above radial groove; medial: posterior humerus below groove; all to olecranon. | Radial. | Elbow extension; long head assists shoulder extension/adduction. |
| Anconeus | Lateral epicondyle to lateral olecranon/proximal posterior ulna. | Radial. | Assists extension, stabilises elbow and abducts ulna slightly during pronation. |
6. Forearm muscles
The anterior compartment is predominantly flexor–pronator and supplied by the median nerve or its anterior interosseous branch, with the ulnar nerve supplying flexor carpi ulnaris and the medial half of flexor digitorum profundus. The posterior/lateral compartment is predominantly extensor–supinator and supplied by the radial nerve or posterior interosseous nerve.
6.1 Anterior flexor–pronator muscles
| Muscle | Proximal → distal attachment | Nerve | Action |
|---|
| Pronator teres | Medial epicondyle/coronoid → lateral mid-radius. | Median. | Pronation; weak elbow flexion. |
| Flexor carpi radialis | Medial epicondyle → bases of 2nd/3rd metacarpals. | Median. | Wrist flexion and radial deviation. |
| Palmaris longus | Medial epicondyle → palmar aponeurosis/flexor retinaculum. | Median. | Tenses palm and assists wrist flexion; may be absent. |
| Flexor carpi ulnaris | Medial epicondyle, olecranon and posterior ulna → pisiform, pisohamate and base 5th metacarpal. | Ulnar. | Wrist flexion and ulnar deviation. |
| Flexor digitorum superficialis | Medial epicondyle/coronoid/radius → middle phalanges 2–5. | Median. | Flexes PIP joints; assists MCP and wrist flexion. |
| Flexor digitorum profundus | Anterior/medial ulna and interosseous membrane → distal phalanges 2–5. | Lateral half AIN; medial half ulnar. | Flexes DIP joints and assists grip. |
| Flexor pollicis longus | Anterior radius/interosseous membrane → distal phalanx of thumb. | Anterior interosseous (median). | Flexes thumb IP joint. |
| Pronator quadratus | Distal anterior ulna → distal anterior radius. | Anterior interosseous (median). | Primary pronator; stabilises distal radioulnar joint. |
6.2 Lateral/posterior extensor–supinator muscles
| Muscle | Proximal → distal attachment | Nerve | Action |
|---|
| Brachioradialis | Lateral supracondylar ridge → distal radius near styloid. | Radial. | Flexes elbow in mid-prone position; returns forearm to neutral. |
| Extensor carpi radialis longus | Lateral supracondylar ridge → base 2nd metacarpal. | Radial. | Extends and abducts wrist. |
| Extensor carpi radialis brevis | Lateral epicondyle → base 3rd metacarpal. | Deep radial. | Extends and abducts wrist; stabilises during grip. |
| Extensor digitorum | Lateral epicondyle → extensor expansions digits 2–5. | Posterior interosseous. | Extends MCP and assists IP extension. |
| Extensor digiti minimi | Lateral epicondyle → little-finger expansion. | Posterior interosseous. | Extends fifth digit. |
| Extensor carpi ulnaris | Lateral epicondyle/posterior ulna → base 5th metacarpal. | Posterior interosseous. | Extends and adducts wrist. |
| Supinator | Lateral epicondyle, annular ligament and ulna → proximal radius. | Deep radial. | Supinates forearm, especially with elbow extended. |
| Abductor pollicis longus | Posterior radius/ulna/interosseous membrane → base 1st metacarpal. | Posterior interosseous. | Abducts/extends thumb at CMC. |
| Extensor pollicis brevis | Posterior radius/interosseous membrane → proximal thumb phalanx. | Posterior interosseous. | Extends thumb MCP. |
| Extensor pollicis longus | Posterior ulna/interosseous membrane → distal thumb phalanx. | Posterior interosseous. | Extends thumb IP; forms medial snuffbox border. |
| Extensor indicis | Posterior distal ulna/interosseous membrane → index expansion. | Posterior interosseous. | Extends index finger independently. |
7. Intrinsic muscles of the hand
| Group | Muscles/attachments | Nerve | Actions |
|---|
| Thenar | Abductor pollicis brevis, flexor pollicis brevis and opponens pollicis from flexor retinaculum/carpals to thumb. | Recurrent median mainly; deep ulnar contribution to deep flexor pollicis brevis. | Thumb abduction, flexion and opposition. |
| Adductor pollicis | Oblique/transverse metacarpal attachments to proximal thumb phalanx. | Deep ulnar. | Adducts thumb and provides pinch force. |
| Hypothenar | Abductor, flexor and opponens digiti minimi from pisiform/hamate to fifth digit. | Deep ulnar. | Moves and cups the little-finger side of the hand. |
| Lumbricals | From FDP tendons to extensor expansions of digits 2–5. | Lateral two median; medial two deep ulnar. | Flex MCP while extending IP joints; important for precision posture. |
| Dorsal interossei | Between metacarpals to proximal phalanges/extensor expansions. | Deep ulnar. | Abduct fingers; assist MCP flexion/IP extension. |
| Palmar interossei | Palmar metacarpals to proximal phalanges/extensor expansions. | Deep ulnar. | Adduct fingers; assist MCP flexion/IP extension. |
The intrinsic muscles position the fingers for writing, buttoning and precision pinch. Extrinsic flexors and extensors generate larger excursion and force; intrinsic and extrinsic muscles must be balanced for efficient hand function.
8. Contractions in everyday tasks
| Task | Concentric examples | Eccentric examples | Isometric/stabilising examples |
|---|
| Reaching to a shelf | Deltoid, serratus anterior and rotator cuff elevate the limb. | Posterior shoulder muscles control return. | Rotator cuff centres humeral head; trunk stabilises. |
| Drinking from a cup | Biceps flexes elbow; wrist/finger flexors grip. | Triceps controls lowering; wrist extensors balance grip. | Scapular muscles hold the shoulder base. |
| Pushing a door | Pectoralis major/triceps/serratus generate push. | Shoulder stabilisers control recoil. | Wrist and hand co-contract to transmit force. |
| Typing | Small finger movements alternate rapidly. | Extensors control key release. | Forearm and shoulder stabilisers maintain position. |
9. Practical assessment and exercise application
- Inspect muscle bulk, posture, scapular position, involuntary movement and substitution patterns.
- Test active range before resisted testing; compare sides and account for pain, fear and fatigue.
- Use a consistent position and lever arm for manual muscle testing; document grade, pain and quality.
- Choose open-chain or closed-chain exercise according to the goal, tissue status and function.
- Progress load, range, speed, repetitions and task complexity gradually; allow recovery.
- Consider nerve roots and peripheral nerve supply when weakness follows a non-muscular pattern.
Clinical scenario: weak shoulder elevation
A patient cannot lift the arm above shoulder height. Observe scapular winging, active versus passive range, pain, deltoid contour and sensation over the lateral shoulder. Compare resisted abduction, external rotation and scapular control. Do not label it a “rotator-cuff tear” from one test; document findings, protect the patient and refer for appropriate clinical evaluation.
10. Examination points and revision questions
High-yield points
- Scapular muscles provide the mobile base; rotator cuff muscles centre the humeral head.
- The anterior arm is mainly musculocutaneous-innervated flexors; the posterior arm is radial-innervated extensors.
- Forearm flexor–pronators are mainly median/ulnar supplied; extensors are radial/posterior interosseous supplied.
- Intrinsic hand muscles coordinate precision grip, thumb opposition and MCP flexion with IP extension.
- Concentric, eccentric and isometric actions must be identified within the task, not by muscle name alone.
- Give the attachments, innervation and actions of the rotator cuff muscles.
- Compare the three heads of triceps and the actions of biceps and brachialis.
- Describe the forearm flexor–pronator and extensor–supinator compartments.
- Explain the roles of lumbricals and interossei in hand function.
- For reaching, drinking and pushing, identify concentric, eccentric and isometric contractions.
- Explain how pain, nerve injury or joint restriction can mimic muscle weakness.
References for further study
Educational note: Muscle testing and exercise prescription require supervised skills training and awareness of injury, surgical and cardiopulmonary precautions.
