Skip to main content
ShapierLab
Understand your body. Shape your progress.
Clear atlas
Structure
Intermediate
8 min read

The tendon

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.
3D scene
The calcaneal tendon at the ankle
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.
Open in the explorer

What a tendon is

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.
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.
Collagen
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.
collagen fibre

Three zones, three behaviours

A tendon is not uniform along its length, and its three regions do not behave the same way.
  • The myotendinous junction is the passage from muscle to tendon. Muscle fibres interdigitate with the collagen there, which increases the contact area.
  • The body of the tendon is the free part, made of parallel bundles aligned along the line of pull.
  • The enthesis 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.
Certainty level · Established
The transition between tendon and bone happens through a zone of gradual composition, not at a sharp boundary.
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.
Standring S (2020) · Neumann DA (2016)

A spring, not just a cable

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.
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.
Elastic return
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.
storage and return

What adapts, and how fast

A tendon adapts to load, as muscle does. But it does so more slowly, and that is the most useful point on this page.

Two tissues, two rhythms

Criterion
Muscle
Tendon
Blood supply
Rich
Poor
Turnover rate
Fast
Slow
Time to visible adaptation
Weeks
Months
Warning signal
Soreness, fatigue
Often late
Certainty level · Probable
The contractile tissue of muscle turns over rapidly after a resistance session.
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.
Damas F, Phillips SM, Vechin FC, Ugrinowitsch C (2015)
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.

Seeing a tendon

The calcaneal tendon at the ankle

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.
Current step
The ankle
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.
Scene description
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.
Visible structures
  • Glenoid labrum
    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.
  • Ligaments of the hip
    Three bands wound around the capsule — iliofemoral, pubofemoral, ischiofemoral. They tighten as the hip extends, which allows standing without continuous muscular effort.
  • Cruciate ligaments
    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.
  • Intervertebral discs
    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.
  • Ligaments of the elbow
    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.
  • Lateral ligaments of the ankle
    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.
Guided steps
  • 1/6
    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.
  • 2/6
    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.
  • 3/6
    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.
  • 4/6
    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.
  • 5/6
    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.
  • 6/6
    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.
Model licence · Z-Anatomy et BodyParts3D — CC-BY-SA 4.0

What the model simplifies

Limit
Only one tendon shown
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.
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.

A subject that calls for care

Caution
What this page does not say
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.
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.
The calcaneal tendon continues the calves and acts on the ankle. The tendons of the forearm muscles drive the hand from a distance, and that of the quadriceps embeds the kneecap at the knee.

Sources

Main sources

  • Standring S (2020). Gray's Anatomy: The Anatomical Basis of Clinical Practice, 42nd edition. Elsevier.
  • Neumann DA (2016). Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation, 3rd edition. Elsevier.
  • Damas F, Phillips SM, Vechin FC, Ugrinowitsch C (2015). A review of resistance training-induced changes in skeletal muscle protein synthesis and their contribution to hypertrophy. Sports Medicine.
Put it into practice in Shapier

See the exercise that loads the calves

Open the calf raise page in Shapier, the exercise that directly loads the calves continued by the calcaneal tendon.
See the exercise that loads the calves
Body Lab explains; Shapier lets you act and track.

Check my understanding

What does a tendon do with the force produced by the muscle?
What does the page say about a tendon's elastic return?
How do the adaptation rhythms of muscle and tendon compare?
Choose an answer

Read next

  • Calves
    The calf brings together the gastrocnemius and the soleus, which share the calcaneal tendon. They push the foot downward, and one of the two also depends on the position of the knee.
    With a 3D scene
  • The ankle
    The talus is wedged between two malleoli like a tenon in a mortise. The ligaments holding it are not symmetrical, and that asymmetry explains a great deal.
    With a 3D scene
  • What limits range of motion
    Four things can stop a movement: bone, capsule, muscle length and the nervous system's tolerance. They do not respond the same way — and not all of them respond at all.
    With a 3D scene

Available offline

Offline download is available in the mobile app.

Trust and method

Author
equipe-editoriale-shapier
Editorial review
Thanh Chau
Scientific review
Pending
Published on
August 2, 2026
Reviewed on August 2, 2026
Next review due August 2, 2027
Limits of this page
  • 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.
Sources
  • Standring S (2020). Gray's Anatomy: The Anatomical Basis of Clinical Practice, 42nd edition. Elsevier.
  • Neumann DA (2016). Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation, 3rd edition. Elsevier.
  • Damas F, Phillips SM, Vechin FC, Ugrinowitsch C (2015). A review of resistance training-induced changes in skeletal muscle protein synthesis and their contribution to hypertrophy. Sports Medicine.
Educational content. Body Lab does not diagnose and does not replace professional advice.
How we work