{"schemaVersion":1,"id":"en-anatomy-triceps-brachii","type":"anatomy","pillar":"body","locale":"en","translationGroupId":"anatomy-triceps-brachii","slugPath":"body/muscles/triceps-brachii","title":"Triceps brachii","shortTitle":"Triceps","summary":"The triceps brachii fills the whole back of the upper arm and extends the elbow. Its long head also crosses the shoulder, which changes its length depending on the position of the arm.","level":"beginner","estimatedMinutes":8,"synonyms":["triceps","triceps brachii","back of the arm","elbow extensor"],"blocks":[{"id":"b1","type":"heading","level":2,"text":"Where the triceps brachii is located","anchor":"where-the-triceps-brachii-is-located"},{"id":"b2","type":"paragraph","content":[{"kind":"text","value":"The triceps brachii fills the entire back compartment of the upper arm on its own, between the shoulder and the elbow. Its bulk accounts for a large share of arm girth, more than the "},{"kind":"link","value":"biceps brachii","href":"/en/body/muscles/biceps-brachii","external":false},{"kind":"text","value":" facing it. Its name comes from its three heads, which start at three different places to join a common tendon."}]},{"id":"b3","type":"heading","level":3,"text":"Origins","anchor":"origins"},{"id":"b4","type":"list","ordered":false,"items":[[{"kind":"text","value":"The long head arises from the infraglenoid tubercle of the shoulder blade, just below the socket of the shoulder joint."}],[{"kind":"text","value":"The lateral head arises from the back surface of the humerus, above the groove of the radial nerve."}],[{"kind":"text","value":"The medial head arises from the back surface of the humerus, below that same groove."}]]},{"id":"b5","type":"paragraph","content":[{"kind":"text","value":"Only the long head takes its support from the shoulder blade. The other two start on the arm bone itself, which makes them indifferent to the position of the shoulder."}]},{"id":"b6","type":"heading","level":3,"text":"Insertion","anchor":"insertion"},{"id":"b7","type":"paragraph","content":[{"kind":"text","value":"The three heads gather into a thick tendon that attaches to the olecranon, the bony point felt at the back of the elbow. Some of the fibres continue into the fascia of the forearm."}]},{"id":"b8","type":"heading","level":3,"text":"Innervation and palpable landmarks","anchor":"innervation-and-palpable-landmarks"},{"id":"b9","type":"paragraph","content":[{"kind":"text","value":"Innervation comes from the radial nerve, from roots C6 to C8. The olecranon is felt immediately; following the back surface of the arm upward, the mass of the triceps can be traced as far as the armpit."}]},{"id":"b10","type":"heading","level":2,"text":"What the triceps brachii does","anchor":"what-the-triceps-brachii-does"},{"id":"b11","type":"paragraph","content":[{"kind":"text","value":"The triceps has one main action and one secondary action."}]},{"id":"b12","type":"list","ordered":false,"items":[[{"kind":"strong","value":"Elbow extension"},{"kind":"text","value":": the three heads straighten the forearm. It is the only substantial muscle group producing this action."}],[{"kind":"strong","value":"Shoulder extension and adduction"},{"kind":"text","value":": the long head, because it also crosses the shoulder joint, draws the arm backward and toward the body."}]]},{"id":"b13","type":"definition","term":"Biarticular muscle","definition":"A muscle that crosses two joints and therefore acts on both. Its total length depends on the combined position of those joints, which changes the force it can produce.","alsoKnownAs":["two-joint muscle"]},{"id":"b14","type":"evidence","level":"established","statement":"The position of the shoulder changes the length of the long head of the triceps, and therefore the tension it can produce at the elbow.","detail":"Like any biarticular muscle, the long head is stretched when the shoulder is flexed with the arm above the head, and shortened when the arm is brought down alongside the body. The principle at work is the length–tension relationship, established on isolated preparations and then confirmed on intact muscle. The practical consequence is that an elbow extension does not load the long head in the same way depending on the orientation of the arm. How large that effect is depends on segment lengths and varies from person to person.","referenceIds":["neumann2016"]},{"id":"b15","type":"heading","level":2,"text":"Seeing the triceps in motion","anchor":"seeing-the-triceps-in-motion"},{"id":"b16","type":"scene3d","sceneId":"grand-pectoral-poussee","title":"The triceps in a pushing movement","intro":"The scene shows the arm during a horizontal push. The triceps shortens as the elbow straightens, while the pectoralis major brings the arms together in front of the chest. Without the 3D, the essential point is that the triceps pulls the olecranon upward, which straightens the forearm.","initialStepId":"step-2","accessibility":{"textAlternative":"A three-dimensional diagram of the upper trunk seen from the front, both arms held out horizontally as at the start of a bench press. The ribcage, sternum, both clavicles, both humeri and the forearms are shown in bone tones, and each shoulder joint is marked by a small dark sphere. Over this frame, pectoralis major is laid out in terracotta as two distinct heads: a thin clavicular head under the collarbone, and a much broader sternocostal head running from the sternum to the humerus, both converging on the same insertion point. The anterior deltoid caps the front of the shoulder and triceps brachii runs along the back of the arm. An animation brings the humeri in front of the chest in horizontal adduction while the belly of pectoralis major thickens. The volumes are deliberately simplified: this is a teaching diagram, not an exact anatomical reconstruction.","structures":[{"label":"Clavicular head","description":"The thin upper portion of pectoralis major, arising from the medial third of the front of the clavicle. Its fibres run down to the humerus, carrying the arm forwards and upwards, and it dominates in incline pushing.","href":"/en/body/muscles/pectoralis-major"},{"label":"Sternocostal head","description":"The broad lower portion, arising from the lateral border of the sternum and the cartilages of the first six ribs. Its fibres run obliquely up to the bicipital groove of the humerus, bringing the arm forwards and downwards.","href":"/en/body/muscles/pectoralis-major"},{"label":"Humeral insertion","description":"Both heads converge into a flat tendon attached to the lateral lip of the bicipital groove of the humerus. The whole origin — clavicle, sternum and ribs — therefore pulls on this single point, which is what makes the line of pull so directional.","href":"/en/body/muscles/pectoralis-major"},{"label":"Anterior deltoid","description":"The front head of the deltoid, arising from the lateral third of the clavicle and inserting on the deltoid tuberosity. It flexes the shoulder and carries the arm forwards, working alongside pectoralis major in every push.","href":"/en/body/muscles/deltoids"},{"label":"Triceps brachii","description":"Three heads joining on the olecranon of the ulna. It extends the elbow and finishes the push: without it the arm closes towards the trunk but the load never actually travels away.","href":"/en/body/muscles/triceps-brachii"}],"steps":[{"id":"charpente","title":"The frame of the push","body":"Pectoralis major does not pull into thin air: it links a wide fixed base — clavicle, sternum and costal cartilages — to a single moving point on the humerus. Locating those bony attachments is already enough to understand its line of pull."},{"id":"faisceau-claviculaire","title":"The clavicular head","body":"The upper portion arises from the medial third of the clavicle. Its fibres run obliquely downwards to the humerus, which gives them a flexing action: they carry the arm forwards and upwards, and dominate in incline pushing."},{"id":"faisceau-sternocostal","title":"The sternocostal head","body":"The much broader lower portion arises from the sternum and the cartilages of the first six ribs. Its fibres run upwards to the humerus, bringing the arm forwards and downwards — the direction of the bench press and the push-up."},{"id":"adduction-horizontale","title":"Horizontal adduction","body":"When the arm starts out to the side and comes back in front of the chest, pectoralis major shortens and its belly thickens. This horizontal adduction is the movement it produces most efficiently, and it sits at the heart of every horizontal push."},{"id":"partenaires","title":"The partners in the push","body":"The anterior deltoid carries the arm forwards, and triceps brachii extends the elbow to finish the movement. None of the three is enough on its own: a horizontal push is always teamwork, which is why fatigue in a single link ends the set."}],"license":"Z-Anatomy et BodyParts3D — CC-BY-SA 4.0"}},{"id":"b17","type":"heading","level":2,"text":"The movements it takes part in","anchor":"the-movements-it-takes-part-in"},{"id":"b18","type":"paragraph","content":[{"kind":"text","value":"The triceps is involved in every movement where the elbow straightens against a resistance, whether that is the "},{"kind":"link","value":"horizontal push","href":"/en/movements/horizontal-push","external":false},{"kind":"text","value":" or the "},{"kind":"link","value":"vertical push","href":"/en/movements/vertical-push","external":false},{"kind":"text","value":". In both cases it works in partnership with a shoulder driver."}]},{"id":"b19","type":"paragraph","content":[{"kind":"text","value":"It also plays a quieter role in the "},{"kind":"link","value":"vertical pull","href":"/en/movements/vertical-pull","external":false},{"kind":"text","value":": the long head, which draws the arm down and back, accompanies the action of the "},{"kind":"link","value":"latissimus dorsi","href":"/en/body/muscles/latissimus-dorsi","external":false},{"kind":"text","value":" while keeping the elbow steady."}]},{"id":"b20","type":"heading","level":2,"text":"Related structures","anchor":"related-structures"},{"id":"b21","type":"heading","level":3,"text":"Synergists","anchor":"synergists"},{"id":"b22","type":"list","ordered":false,"items":[[{"kind":"text","value":"The anconeus, a small muscle at the back of the elbow, assists extension and stabilises the joint."}],[{"kind":"text","value":"The "},{"kind":"link","value":"pectoralis major","href":"/en/body/muscles/pectoralis-major","external":false},{"kind":"text","value":" and the anterior head of the "},{"kind":"link","value":"deltoid","href":"/en/body/muscles/deltoids","external":false},{"kind":"text","value":" supply the shoulder movement while the triceps straightens the elbow."}]]},{"id":"b23","type":"heading","level":3,"text":"Antagonists","anchor":"antagonists"},{"id":"b24","type":"list","ordered":false,"items":[[{"kind":"text","value":"The "},{"kind":"link","value":"biceps brachii","href":"/en/body/muscles/biceps-brachii","external":false},{"kind":"text","value":" and the brachialis flex the elbow, the opposite action to that of the triceps."}],[{"kind":"text","value":"The brachioradialis also contributes to flexion, especially with the forearm in a neutral position."}]]},{"id":"b25","type":"paragraph","content":[{"kind":"text","value":"In a fast movement, agonists and antagonists often contract together at the end of the range to slow the segment down and protect the joint."}]},{"id":"b26","type":"heading","level":2,"text":"What the 3D model simplifies","anchor":"what-the-3d-model-simplifies"},{"id":"b27","type":"callout","tone":"limit","title":"Three overlapping heads","content":[[{"kind":"text","value":"On the model, the three heads are shown side by side so they stay readable. In reality the medial head is almost entirely covered by the other two, and its fibres blend into the common tendon over a long stretch."}],[{"kind":"text","value":"The terminal tendon is drawn as a simple band. In an individual, the attachment surface on the olecranon, the presence of accessory fibres and the shape of the muscle all vary. The model illustrates a typical arrangement, never a personal anatomy."}]]},{"id":"b28","type":"heading","level":2,"text":"Sources","anchor":"sources"},{"id":"b29","type":"sourceList","title":"Key sources","referenceIds":["standring2020","neumann2016"]},{"id":"b30","type":"shapierAction","actionId":"exercises-extensions-triceps","label":"See the triceps extensions exercise","description":"See in Shapier the triceps extensions exercise, which trains the elbow extension described on this page.","webTarget":"https://shapier.app/en/exercises/extensions-triceps","appTarget":"shapier://exercises/extensions-triceps"},{"id":"b31","type":"quiz","title":"Check my understanding","questions":[{"id":"q1","prompt":"Why does shoulder position change the work of the long head, but not of the lateral and medial heads?","choices":[{"id":"q1c1","label":"Because the long head arises from the shoulder blade and crosses the shoulder, while the other two start on the humerus","correct":true,"explanation":"The page states that only the long head takes its support from the shoulder blade; the other heads are indifferent to the position of the shoulder."},{"id":"q1c2","label":"Because the long head is the only one innervated by the radial nerve","correct":false,"explanation":"Tempting since the radial nerve supplies the triceps, but the page says this innervation, from roots C6 to C8, covers the whole muscle, not a single head."},{"id":"q1c3","label":"Because the long head is the largest of the three","correct":false,"explanation":"The page does not base this difference on size: crossing the shoulder is what changes the length of the long head."}]},{"id":"q2","prompt":"What role does the triceps play in the vertical pull?","choices":[{"id":"q2c1","label":"A quieter one: the long head accompanies the latissimus dorsi by drawing the arm down and back, while keeping the elbow steady","correct":true,"explanation":"Exactly what the page describes, because the long head also crosses the shoulder joint."},{"id":"q2c2","label":"It is the main driver of the vertical pull","correct":false,"explanation":"The driver of the pull is the latissimus dorsi; the triceps only accompanies its action."},{"id":"q2c3","label":"It plays no role, since it only straightens the elbow","correct":false,"explanation":"Plausible because elbow extension is its main action, but the long head also extends the shoulder, hence this secondary role in pulling."}]},{"id":"q3","prompt":"On the 3D model, the three heads are shown side by side. What should you take from that?","choices":[{"id":"q3c1","label":"That it is a simplification: in reality, the medial head is almost entirely covered by the other two","correct":true,"explanation":"The block on what the 3D model simplifies says so explicitly, adding that its fibres blend into the common tendon over a long stretch."},{"id":"q3c2","label":"That this is the actual arrangement of the heads in everyone","correct":false,"explanation":"The page stresses that the model illustrates a typical arrangement, never a personal anatomy."},{"id":"q3c3","label":"That the medial head is the most superficial of the three","correct":false,"explanation":"It is the opposite: the page says it is largely hidden beneath the other two heads."}]}]},{"id":"b32","type":"relatedContent","title":"Read next","targetIds":["en-anatomy-pectoralis-major","en-anatomy-deltoids","en-anatomy-biceps-brachii"]}],"relations":[{"type":"produces-movement","targetId":"en-movement-horizontal-push"},{"type":"produces-movement","targetId":"en-movement-vertical-push"},{"type":"uses-structure","targetId":"en-anatomy-pectoralis-major"},{"type":"next-step","targetId":"en-mechanism-how-muscle-grows"}],"authors":["equipe-editoriale-shapier"],"reviewers":["Thanh Chau"],"references":[{"id":"standring2020","authors":"Standring S","year":2020,"title":"Gray's Anatomy: The Anatomical Basis of Clinical Practice, 42nd edition","source":"Elsevier","kind":"book","url":"https://shop.elsevier.com/books/grays-anatomy/standring/978-0-7020-7705-0"},{"id":"neumann2016","authors":"Neumann DA","year":2016,"title":"Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation, 3rd edition","source":"Elsevier","kind":"book","url":"https://shop.elsevier.com/books/kinesiology-of-the-musculoskeletal-system/neumann/978-0-323-28753-1"}],"review":{"publishedAt":"2026-08-02","reviewedAt":"2026-08-02","reviewDueAt":"2027-08-02","evidenceLevel":"established"},"limitations":["The lateral and medial heads partly overlap on the 3D model, whereas the medial head is largely hidden beneath the other two.","The anconeus, which functionally extends the triceps, is not drawn separately in the scene.","The page describes joint actions; it does not say which head contributes most to a given exercise, since that depends on shoulder position and load."],"seo":{"title":"Triceps brachii — anatomy, heads and elbow function","description":"Origins, insertion and actions of the three heads of the triceps brachii, its synergists and the pushing movements it takes part in.","canonicalPath":"/en/body/muscles/triceps-brachii","image":"/og/en/anatomy-triceps-brachii.png"},"app":{"offlineEligible":true},"version":1}