The body: muscles, landmarks and functions

The Body pillar answers a single question: where is a structure and what does it do?

Every page starts from a muscle and works back up to the movement. Position in the body, attachment areas on the skeleton, actions produced, movements involved: the goal is not to memorise an atlas, but to recognise what is working when you push, pull, bend or stabilise.

A muscular structure only means something once it is tied to an action. The structure pages therefore follow the same progression.

Three entry points lead to the same content, depending on what you are looking for.

None of these entry points takes priority, and the pages can be read in any order. If you do not know where to start, the muscles easiest to find on yourself are the pectoralis major, the deltoid and the quadriceps.

Body Lab describes a reference anatomy: the one taught and depicted in functional anatomy textbooks. It matches no individual's build exactly. Muscle size, fibre orientation and the extent of attachments vary from person to person, and some variants are common enough to be described as normal.

The first twelve are the prime movers of the basic movements: pushing, pulling, squatting and hinging at the hip. Six more have since joined them, of a different kind. Four belong to the deep plane — rotator cuff, serratus anterior, iliopsoas and hip adductors — and are visible on no silhouette: they orient and stabilise more than they move. The last two, forearm muscles and tibialis anterior, occupy the distal segments, where the force produced by the large muscles has to pass to reach the ground or the bar.

Four of them were written because the corpus named them without describing them: gluteus medius appeared on six pages, the rhomboids on five, tensor fasciae latae on four. The diaphragm came in through the same door, with a twist: one of the pages naming it did so to point out that it was missing from the scene. A last one describes not a muscle but the part linking them all to bone: the tendon.

Cross-cutting pages describe no particular structure but what structures are made of. Four cover the tissues the corpus named without describing them — bone, cartilage, the tendon and fascia — and three cover what runs through every muscle: muscle fibres, what limits range of motion and contraction regimes. The last was written for the same reason as the muscles named above: the word "eccentric" appeared on fourteen pages, redefined locally each time.

Until now this hub announced that the nervous, circulatory and respiratory systems would not be covered, for want of being able to show them. The position has changed on one point, and one only: being unable to show a system does not require saying nothing about it, as long as the absence of a model is declared on every page. The precedent already existed — fascia, cartilage and motor command are described without a scene and say so.

The nervous system opens the series. It was named on twenty-six pages — every muscle gives its nerve supply — without any of them saying how it is organised. Two pages extend it: the neuron, whose signal never varies in size but only in rate, and the neuromuscular junction, which closes the one missing link between the nerve command and the sliding of the filaments.

The brain comes next, with two pages following directly from it. Motor control shows that a fast movement is launched according to a prediction rather than steered, because feedback arrives too late to correct it. Proprioception describes the channel supplying that feedback — the one that lets you touch your nose with your eyes closed, and that knows well where the body is but rather poorly what it is producing.

Three pages close the vital foundation. The heart gives the Energy pillar the equation it was missing, and corrects a formula everybody applies. Blood and circulation describes what the word "blood" covered across thirty-two pages. The lungs complete the diaphragm page and establish a fact that contradicts the sensation: in healthy adults, breath is not what limits an endurance effort.

Two pages close the series. The endocrine system is the body's second communication network — slow and diffuse where the nerve is fast and targeted — and corrects along the way the idea that the post-session hormonal surge drives muscle growth. Pain was used on forty-six pages as a border and never as a subject; it becomes one, with the distinction that matters — the signal sent is not the experience lived — and a firm reminder of what that distinction above all does not let you conclude.

Three pages finally complete the foundation. The digestive system is the backbone of the three pages on nutrients, all of which assumed a route nothing described. The skin carries a function the corpus took for granted: shedding the heat the muscle produces. The immune system says what the word "inflammation" covers, used by two pages without ever being defined.

Three pages close the list. The kidneys are not waste filters but regulators, and they carry the answer the hydration page assumed. The lymphatic system is the return network three pages already invoked — the route dietary fat takes and the highway of the defence cells. Balance brings together three independent pieces of information the brain must reconcile, and shows that standing is not a state but a permanent correction.

None of these pages has a scene, and each explains why. Three reasons are spread among them: the anatomical source does not contain the tissue, the scale is beyond a mesh's reach, or — for the digestive system and the kidneys — the data exists but under a licence the project cannot use.

The joints have since joined the pillar. They follow a different logic from the muscles: what is described is not a motor but a trade-off between mobility and restraint, and that trade-off is not the same from one joint to the next.

The shoulder and the hip are the two extremes — the first trades stability for range, the second does the reverse. The knee has neither by its shape and depends entirely on its ligaments and menisci. The lumbar spine moves only a few degrees per level, and it is their sum that gives the trunk its range. The elbow houses two mechanisms in one capsule — a hinge and a pivot — and the ankle owes its reputation to an asymmetry: its outer ligaments are far thinner than the inner ones.

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.

This pillar is the starting point for the others. Once a structure has been identified, the Movement pillar shows how several muscles coordinate to produce a movement, the Adaptation pillar explains how that muscle changes when it is worked repeatedly, and the Energy pillar describes the fuel that contraction consumes.