The joints

Six pages, and one question asked six times: what does this joint give up, and for what? No two answer it the same way.

A muscle page describes a motor. A joint page describes a trade-off: every degree of mobility gained is paid for in restraint, and the other way round. The six joints described here do not settle that trade-off the same way, and that is what makes them comparable.

The two extremes

The shoulder and the hip have the same shape — a ball in a socket — and the opposite choice. The shoulder trades stability for the widest range in the body; the hip does the reverse, with a deep socket gripping the head of the femur.

The ones that depend on something other than their shape

The knee has neither the hip's stability nor the shoulder's range from its geometry: it depends entirely on its ligaments and menisci.

The ankle owes its reputation to an asymmetry — its outer ligaments are far thinner than the inner ones.

The ones that add up

The lumbar spine moves only a few degrees per level. It is their sum that gives the trunk its range, and that distribution explains more than a global figure does.

The elbow houses two mechanisms in one capsule: a hinge and a pivot.

What stops them

One cross-cutting page ties them together: what limits range of motion separates the four things that can stop a movement, and explains why one instruction produces different positions in different people. Proprioception supplies part of the answer: what often stops a stretch is not a mechanical stop but a sensation.

On the material side, cartilage and bone describe what those surfaces are made of.

Put it into practice in Shapier

Put mobility and recovery into practice

Putting mobility and recovery work together into a routine happens in Shapier; Body Lab only explains what each joint trades, and why.

Put mobility and recovery into practice

Body Lab explains; Shapier lets you act and track.

The six joints

The shoulder
The most mobile joint in the body, and the one that holds least by its shape. A wide head resting on a shallow socket, retained by soft tissue.
With a 3D scene
The hip
A sphere set deep in a socket, locked by three ligaments that tighten in extension. That is what makes standing possible without continuous muscular effort.
With a 3D scene
The knee
Two poorly matched surfaces, an almost flat plateau under rounded condyles. Menisci, cruciate and collateral ligaments make up for that lack of fit.
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
The lumbar spine
Five vertebrae, five discs and a set of ligaments. Each level moves only a few degrees: it is their sum that gives the trunk its range.
With a 3D scene
The elbow
Two mechanisms inside one capsule: a hinge that bends the arm, and a pivot that turns the palm over. The radius rotates in place, held by a ring.
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

This index page describes how a set is organised; the anatomical descriptions, their sources and their limits sit on the pages themselves.
None of these pages assesses an individual situation. Joint pain that persists, that follows an impact or that comes with swelling belongs to a health professional.

Educational content. Body Lab does not diagnose and does not replace professional advice.

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