{"schemaVersion":1,"id":"en-anatomy-tendon","type":"anatomy","pillar":"body","locale":"en","translationGroupId":"anatomy-tendon","slugPath":"body/the-tendon","title":"The tendon","shortTitle":"Tendon","summary":"The part that links a muscle to a bone. It transmits force, briefly stores it like a spring, and adapts far more slowly than the muscle it continues.","level":"intermediate","estimatedMinutes":8,"synonyms":["tendon","calcaneal tendon","Achilles tendon","collagen","insertion","myotendinous junction","enthesis"],"blocks":[{"id":"b1","type":"heading","level":2,"text":"What a tendon is","anchor":"what-a-tendon-is"},{"id":"b2","type":"paragraph","content":[{"kind":"text","value":"The pages in the Body pillar name a tendon for every muscle described: the tendon of the long head of the biceps, the quadriceps tendon, the calcaneal tendon. None had yet said what this part is."}]},{"id":"b3","type":"paragraph","content":[{"kind":"text","value":"A tendon is a cord of fibrous tissue linking a muscle to a bone. It is not contractile: it does not shorten and produces no force. It transmits the force the muscle produces, and it transmits it far — which is what allows slender fingers to be driven by muscle masses sitting near the elbow."}]},{"id":"b4","type":"definition","term":"Collagen","definition":"A protein in long fibres, the main constituent of tendons, ligaments and fascia. Its fibres align along the line of pull, making the tissue very strong in that direction and much less so in others.","alsoKnownAs":["collagen fibre"]},{"id":"b5","type":"heading","level":2,"text":"Three zones, three behaviours","anchor":"three-zones-three-behaviours"},{"id":"b6","type":"paragraph","content":[{"kind":"text","value":"A tendon is not uniform along its length, and its three regions do not behave the same way."}]},{"id":"b7","type":"list","ordered":false,"items":[[{"kind":"text","value":"The "},{"kind":"strong","value":"myotendinous junction"},{"kind":"text","value":" is the passage from muscle to tendon. Muscle fibres interdigitate with the collagen there, which increases the contact area."}],[{"kind":"text","value":"The "},{"kind":"strong","value":"body of the tendon"},{"kind":"text","value":" is the free part, made of parallel bundles aligned along the line of pull."}],[{"kind":"text","value":"The "},{"kind":"strong","value":"enthesis"},{"kind":"text","value":" is the attachment to bone. The tissue changes nature gradually there, from tendon to fibrocartilage to bone, which avoids an abrupt transition between two materials of very different stiffness."}]]},{"id":"b8","type":"evidence","level":"established","statement":"The transition between tendon and bone happens through a zone of gradual composition, not at a sharp boundary.","detail":"Descriptive anatomy and kinesiology describe the same organisation in successive layers. The arrangement spreads stress over a thickness instead of concentrating it on a line — the same principle as a cable clamp.","referenceIds":["standring2020","neumann2016"]},{"id":"b9","type":"heading","level":2,"text":"A spring, not just a cable","anchor":"a-spring-not-just-a-cable"},{"id":"b10","type":"paragraph","content":[{"kind":"text","value":"The cable image is useful but incomplete. A tendon lets itself be stretched by a few per cent under load, then returns part of that energy as it comes back to length."}]},{"id":"b11","type":"paragraph","content":[{"kind":"text","value":"The calcaneal tendon is the clearest example. On every running stride it lengthens on landing and shortens on push-off; part of the work comes from that return rather than from a contraction. That is also why it is so thick: it works continuously, under forces well above body weight."}]},{"id":"b12","type":"definition","term":"Elastic return","definition":"The ability of a tissue to store energy by deforming, then give it back as it regains its shape. It creates no energy: it recovers part of what would otherwise be dissipated.","alsoKnownAs":["storage and return"]},{"id":"b13","type":"heading","level":2,"text":"What adapts, and how fast","anchor":"what-adapts-and-how-fast"},{"id":"b14","type":"paragraph","content":[{"kind":"text","value":"A tendon adapts to load, as muscle does. But it does so more slowly, and that is the most useful point on this page."}]},{"id":"b15","type":"comparison","title":"Two tissues, two rhythms","columns":["Criterion","Muscle","Tendon"],"rows":[{"label":"Blood supply","cells":["Rich","Poor"]},{"label":"Turnover rate","cells":["Fast","Slow"]},{"label":"Time to visible adaptation","cells":["Weeks","Months"]},{"label":"Warning signal","cells":["Soreness, fatigue","Often late"]}]},{"id":"b16","type":"evidence","level":"probable","statement":"The contractile tissue of muscle turns over rapidly after a resistance session.","detail":"The review covers muscle protein synthesis and describes a response measurable within hours, with structural change over weeks. It does not measure tendon: the comparison drawn here rests on the poor tendon blood supply described by anatomy, and remains a general trend rather than a figure.","referenceIds":["damas2016"]},{"id":"b17","type":"paragraph","content":[{"kind":"text","value":"That difference in rhythm explains a common situation: the capacity to produce force can improve faster than the tendon's tolerance to that force. Body Lab draws no training rule from this — it is an observation about structure, not an instruction."}]},{"id":"b18","type":"heading","level":2,"text":"Seeing a tendon","anchor":"seeing-a-tendon"},{"id":"b19","type":"scene3d","sceneId":"articulations","title":"The calcaneal tendon at the ankle","intro":"The scene shows the calcaneal tendon running down behind the ankle to the heel bone. It leaves the frame at the top, which is faithful: it continues up to the [calves](/en/body/muscles/calves), whose three heads it continues. Without the 3D, the picture fits in one sentence: a thick cord stretched from calf to heel, passing behind the joint.","initialStepId":"cheville","accessibility":{"textAlternative":"A three-dimensional model of four joints from the left side of the body, presented one after another on a paper background. The shoulder shows the shoulder blade, collarbone and upper humerus in bone tones, with the joint capsule, the glenoid labrum and the glenohumeral ligaments in olive grey. The hip shows the hip bone and femur, the capsule wrapping the neck, the acetabular labrum and the three ligaments wound around it. The knee shows the femur, tibia, fibula and kneecap, with the two menisci resting on the tibial plateau, the cruciate ligaments at the centre and the collaterals on either side. The lumbar spine, seen from the side, shows the five vertebrae and the sacrum separated by five discs, with the longitudinal ligaments running in front of and behind the vertebral bodies. The joint tissues are highlighted at each step, the bones staying in the background.","structures":[{"label":"Glenoid labrum","description":"A fibrocartilaginous rim fixed around the edge of the glenoid cavity. It deepens the socket and increases the contact area with the head of the humerus, whose diameter far exceeds that of the cavity.","href":"/en/body/joints/shoulder"},{"label":"Ligaments of the hip","description":"Three bands wound around the capsule — iliofemoral, pubofemoral, ischiofemoral. They tighten as the hip extends, which allows standing without continuous muscular effort.","href":"/en/body/joints/hip"},{"label":"Cruciate ligaments","description":"Two ligaments stretched across the centre of the knee, crossing one in front of the other. They limit the tibia sliding under the femur — forwards for the anterior, backwards for the posterior.","href":"/en/body/joints/knee"},{"label":"Intervertebral discs","description":"Five discs separate the lumbar vertebrae and the sacrum. Each pairs a tough fibrous ring with a more deformable core, which spreads load and allows slight movement between two neighbouring vertebrae.","href":"/en/body/joints/lumbar-spine"},{"label":"Ligaments of the elbow","description":"Two collateral ligaments hold the elbow from the sides, and a ring encircles the head of the radius so it can pivot without leaving its place. The elbow thus combines a hinge and a pivot.","href":"/en/body/joints/elbow"},{"label":"Lateral ligaments of the ankle","description":"Three slender bands link the fibula to the talus and the heel bone. They are markedly thinner than their medial counterparts, which is why the ankle is more easily forced inwards.","href":"/en/body/joints/ankle"}],"steps":[{"id":"epaule","title":"The shoulder","body":"The head of the humerus is far wider than the socket that receives it. The glenoid labrum deepens the rim, the capsule wraps the whole, and three glenohumeral ligaments reinforce it in front. That is the price of mobility: little bone to hold, a great deal of soft tissue."},{"id":"hanche","title":"The hip","body":"Unlike the shoulder, the femoral head sits deep in the socket, which the acetabular labrum extends further. The three ligaments wind around the neck and tighten in extension: standing, they carry part of the work the muscles no longer have to supply."},{"id":"genou","title":"The knee","body":"Two poorly matched surfaces — the rounded condyles of the femur on an almost flat tibial plateau. The menisci fill the gap, the cruciates hold the tibia front to back, the collaterals hold it side to side. Remove any one of these parts and the load shifts onto the others."},{"id":"rachis-lombaire","title":"The lumbar spine","body":"Five vertebrae, five discs, and a set of ligaments running the whole height. Each level moves only a few degrees; it is their sum that gives the trunk its range. The longitudinal ligaments limit flexion and extension, the ligamenta flava close the back of the canal."},{"id":"coude","title":"The elbow","body":"The elbow does two things inside one capsule. The humerus and ulna form a hinge that flexes and extends in a single plane; the head of the radius pivots in place inside a ligamentous ring, which turns the palm over. The two collateral ligaments hold it all from the sides."},{"id":"cheville","title":"The ankle","body":"The talus is wedged between the two malleoli like a tenon in a mortise. On the inner side, a thick fan-shaped ligament; on the outer side, three markedly thinner bands. That asymmetry is no detail: it explains which way the ankle most often gives."}],"license":"Z-Anatomy et BodyParts3D — CC-BY-SA 4.0"}},{"id":"b20","type":"heading","level":2,"text":"What the model simplifies","anchor":"what-the-model-simplifies"},{"id":"b21","type":"callout","tone":"limit","title":"Only one tendon shown","content":[[{"kind":"text","value":"The calcaneal is the only tendon extracted separately. All the others are merged into the muscle volumes of the model: the boundary between the belly and its tendon is not drawn there, although it is clear in a body."}],[{"kind":"text","value":"The synovial sheaths in which tendons slide as they curve around a bone are not represented either. They nonetheless matter to how the hand and the ankle work."}]]},{"id":"b22","type":"heading","level":2,"text":"A subject that calls for care","anchor":"a-subject-that-calls-for-care"},{"id":"b23","type":"callout","tone":"caution","title":"What this page does not say","content":[[{"kind":"text","value":"Tendon pain is common and carries names that circulate widely. Describing the structure of a tendon in no way allows a pain to be attributed to one of them, or its state to be assessed."}],[{"kind":"text","value":"Body Lab proposes here no exercise, no loading protocol and no timeline. Tendon discomfort that settles in, that appears at rest, or that limits a usual movement belongs to a health professional."}]]},{"id":"b24","type":"heading","level":2,"text":"Related structures","anchor":"related-structures"},{"id":"b25","type":"paragraph","content":[{"kind":"text","value":"The calcaneal tendon continues the "},{"kind":"link","value":"calves","href":"/en/body/muscles/calves","external":false},{"kind":"text","value":" and acts on the "},{"kind":"link","value":"ankle","href":"/en/body/joints/ankle","external":false},{"kind":"text","value":". The tendons of the "},{"kind":"link","value":"forearm muscles","href":"/en/body/muscles/forearm","external":false},{"kind":"text","value":" drive the hand from a distance, and that of the "},{"kind":"link","value":"quadriceps","href":"/en/body/muscles/quadriceps","external":false},{"kind":"text","value":" embeds the kneecap at the "},{"kind":"link","value":"knee","href":"/en/body/joints/knee","external":false},{"kind":"text","value":"."}]},{"id":"b26","type":"heading","level":2,"text":"Sources","anchor":"sources"},{"id":"b27","type":"sourceList","title":"Main sources","referenceIds":["standring2020","neumann2016","damas2016"]},{"id":"b28","type":"shapierAction","actionId":"exercises-calf-raises","label":"See the exercise that loads the calves","description":"Open the calf raise page in Shapier, the exercise that directly loads the calves continued by the calcaneal tendon.","webTarget":"https://shapier.app/en/exercises/calf-raises","appTarget":"shapier://exercises/calf-raises"},{"id":"b29","type":"quiz","title":"Check my understanding","questions":[{"id":"q1","prompt":"What does a tendon do with the force produced by the muscle?","choices":[{"id":"q1c1","label":"It transmits it to the bone, without producing any itself","correct":true,"explanation":"The page states that a tendon is not contractile: it does not shorten and produces no force; it transmits the muscle's force, and transmits it far."},{"id":"q1c2","label":"It produces part of it by shortening, like the muscle","correct":false,"explanation":"Tempting because the tendon continues the muscle, but the page says it is not contractile: it does not shorten and produces no force."},{"id":"q1c3","label":"It links two bones together to stabilise the joint","correct":false,"explanation":"A common mix-up with ligaments: the page defines the tendon as a cord linking a muscle to a bone."}]},{"id":"q2","prompt":"What does the page say about a tendon's elastic return?","choices":[{"id":"q2c1","label":"It recovers part of the energy that would otherwise be dissipated","correct":true,"explanation":"The tendon stretches by a few per cent under load, then gives part of that energy back as it returns to length, without creating any."},{"id":"q2c2","label":"It creates energy that adds to the work of contraction","correct":false,"explanation":"The spring image pushed too far: the page says explicitly that elastic return creates no energy, it recovers part of it."},{"id":"q2c3","label":"It concerns only the calcaneal tendon","correct":false,"explanation":"The calcaneal is the clearest example, but the page describes this behaviour for any tendon under load."}]},{"id":"q3","prompt":"How do the adaptation rhythms of muscle and tendon compare?","choices":[{"id":"q3c1","label":"The tendon adapts to load more slowly than the muscle","correct":true,"explanation":"The page's table sets weeks for muscle against months for tendon: the capacity to produce force can improve faster than the tendon's tolerance to it."},{"id":"q3c2","label":"The tendon adapts at the same pace as the muscle","correct":false,"explanation":"The table contrasts two tissues: rich blood supply and fast turnover for muscle, poor blood supply and slow turnover for tendon."},{"id":"q3c3","label":"Tendon discomfort always warns early, before the muscle tires","correct":false,"explanation":"The table states the opposite: the tendon's warning signal is often late, whereas the muscle signals through soreness and fatigue."}]}]},{"id":"b30","type":"relatedContent","title":"Read next","targetIds":["en-anatomy-calves","en-anatomy-ankle-joint","en-mechanism-range-of-motion"]}],"relations":[{"type":"uses-structure","targetId":"en-anatomy-calves"},{"type":"explains","targetId":"en-anatomy-ankle-joint"},{"type":"prerequisite","targetId":"en-mechanism-how-muscle-grows"},{"type":"next-step","targetId":"en-mechanism-range-of-motion"}],"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"},{"id":"damas2016","authors":"Damas F, Phillips SM, Vechin FC, Ugrinowitsch C","year":2015,"title":"A review of resistance training-induced changes in skeletal muscle protein synthesis and their contribution to hypertrophy","source":"Sports Medicine","kind":"review","doi":"10.1007/s40279-015-0320-0"}],"review":{"publishedAt":"2026-08-02","reviewedAt":"2026-08-02","reviewDueAt":"2027-08-02","evidenceLevel":"established"},"limitations":["The scene shows only one tendon, the calcaneal: the others are merged into the muscle volumes of the model, and the boundary between belly and tendon is not drawn there.","The adaptation rates quoted describe a general trend drawn from work on muscle: data specific to human tendon are fewer and more scattered.","This page describes a structure. It cannot identify a tendinopathy or judge a pain: tendon discomfort that settles in belongs to a health professional."],"seo":{"title":"The tendon — transmission, elasticity and slow adaptation","description":"What a tendon is, how it transmits and returns force, why it adapts more slowly than muscle, and what the 3D does not show of it.","canonicalPath":"/en/body/the-tendon","image":"/og/en/anatomy-tendon.png"},"app":{"offlineEligible":true},"version":1}