{"schemaVersion":1,"id":"en-video-muscle-growth","type":"video","pillar":"adaptation","locale":"en","translationGroupId":"video-muscle-growth","slugPath":"videos/how-muscle-grows","title":"How muscle grows — the video","shortTitle":"Muscle growth","summary":"An animation that follows a muscle fibre from the mechanical signal produced during effort through to the contractile proteins added over the following days. The page carries the same content in text, with its sources and the limits of the simplification.","level":"beginner","estimatedMinutes":8,"synonyms":["hypertrophy","muscle growth","building muscle","mechanical tension","training volume"],"blocks":[{"id":"b1","type":"paragraph","content":[{"kind":"text","value":"A muscle does not grow during the session. It receives a signal during the session, then changes over the hours and days that follow. This video makes that order of events visible, which is hard to grasp from a written definition alone."}]},{"id":"b2","type":"videoLesson","videoId":"croissance-musculaire","title":"How muscle grows"},{"id":"b3","type":"heading","level":2,"text":"What the video shows","anchor":"what-the-video-shows"},{"id":"b4","type":"paragraph","content":[{"kind":"text","value":"The animation starts from a muscle fibre at rest, then applies a resistance it has to overcome several times in a row. The shot tightens onto the sarcomeres, the contractile units lined up end to end inside the fibre. You watch them shorten under load, then lengthen again: this is "},{"kind":"term","value":"mechanical tension","definition":"the force placed on the contractile structures when a muscle works against a resistance"},{"kind":"text","value":"."}]},{"id":"b5","type":"paragraph","content":[{"kind":"text","value":"The next sequence moves from mechanics to chemistry. The repeated stress sets off a cascade of signals inside the fibre, shown as points of light travelling towards the cell nucleus. This passage is the heart of the video: it shows that the load adds no material, it asks the cell to build some."}]},{"id":"b6","type":"paragraph","content":[{"kind":"text","value":"The final shot jumps forward several days. New contractile proteins have been slotted in along the existing sarcomeres, and the cross-section of the fibre has grown slightly. The animation then rewinds to run the cycle again, because one session on its own is not enough: it is the repetition of the signal that produces a measurable change."}]},{"id":"b7","type":"definition","term":"Hypertrophy","definition":"An increase in the size of existing muscle fibres, distinct from an increase in their number. It is what the closing shot of the video shows.","alsoKnownAs":["muscle growth","gain in cross-section"]},{"id":"b8","type":"heading","level":2,"text":"The signal first, the building afterwards","anchor":"the-signal-first-the-building-afterwards"},{"id":"b9","type":"paragraph","content":[{"kind":"text","value":"The video deliberately separates two moments that training tends to blur together. During the session, the fibre is placed under stress and responds to it biologically. After the session, it uses the amino acids available to renew and to add contractile proteins. That rebuilding phase depends as much on food and rest as on the load lifted."}]},{"id":"b10","type":"evidence","level":"established","statement":"Resistance training sets off a protein-building response in the muscle worked, and that response happens after the effort rather than during it.","detail":"Review articles describe mechanical tension as the main trigger, alongside metabolic stress and micro-damage, and document a transient rise in muscle protein synthesis after a bout of resistance exercise. The exact share of each mechanism in the final result is not established, and the measurements come mostly from young, healthy adults studied in a laboratory.","referenceIds":["schoenfeld2010","atherton2012"]},{"id":"b11","type":"heading","level":2,"text":"What repetition changes","anchor":"what-repetition-changes"},{"id":"b12","type":"paragraph","content":[{"kind":"text","value":"The rewind at the end of the video is not an editing flourish. The amount of work accumulated over a week is one of the best documented parameters of muscle growth, more so than the fine detail of any single exercise."}]},{"id":"b13","type":"evidence","level":"probable","statement":"Weekly training volume per muscle group and protein availability both shape how large the gains in muscle mass turn out to be.","detail":"A meta-analysis of resistance training programmes describes a graded relationship between the number of sets performed each week for a muscle group and the increase in muscle mass observed. A separate meta-analysis, carried out in healthy adults, links additional protein intake to greater gains in mass and strength, with an effect that stops rising beyond roughly 1.6 grams of protein per kilogram of body weight per day. Those figures are group averages: they describe a population trend, not an individual prescription.","referenceIds":["schoenfeld2017volume","morton2018"]},{"id":"b14","type":"heading","level":2,"text":"The linked scene","anchor":"the-linked-scene"},{"id":"b15","type":"scene3d","sceneId":"chronologie-adaptation","title":"Timeline of muscular adaptation","intro":"The same sequence as the video, but explorable step by step: stress during the effort, signalling in the hours that follow, protein building over several days, then a return to the starting point for the next session. Every step is described in text below the scene, and stays readable without displaying the model.","accessibility":{"textAlternative":"Timeline diagram: five evenly spaced stations along a horizontal time axis, each topped by a muscle fibre drawn as a vertical capsule. From left to right the stations stand for the training session, the damage and the signalling it triggers, the period of elevated protein synthesis, the remodelling of the fibre, and the new fibre size that results. The capsules grow slightly wider from one station to the next, while a cluster of small spheres above each station shows how intense the signalling is: a schematic dumbbell at the first station, the densest cluster at the third, almost nothing at the fifth. A marker in front of the axis points at the current stage and moves from station to station. The volumes are reading aids: neither the proportions nor the durations are to scale.","structures":[{"label":"Training session","description":"A demanding set puts mechanical tension on the fibres that are working. It triggers everything that follows, but it is not yet an adaptation.","href":"/en/adaptations/mechanical-tension-fatigue-and-volume"},{"label":"Cellular signals","description":"The effort disturbs the inside of the fibre and sets off chemical signals. These signals build nothing on their own: they direct what the cell does next.","href":"/en/adaptations/how-muscle-grows"},{"label":"Elevated protein synthesis","description":"In response to the signals, the fibre makes proteins faster than it breaks them down. This rise is temporary and settles back toward its usual level.","href":"/en/adaptations/muscle-protein-synthesis"},{"label":"New fibre size","description":"The cross-section of the fibre only grows through repeated cycles. The diameter shown here is a reading aid, not a measurement.","href":"/en/adaptations/how-muscle-grows"},{"label":"Time axis","description":"The axis orders the events from left to right. The intervals are evenly spaced for legibility: they do not represent real durations."}],"steps":[{"id":"seance","title":"1. The training session","body":"A demanding enough set puts mechanical tension on the fibres that are working. At this point nothing has changed yet in the structure of the muscle: the session is a signal, not a gain."},{"id":"degats-signalisation","title":"2. Damage and signalling","body":"The effort disturbs the inside of the fibre and sets off a cascade of chemical signals. They tell the cell to repair and reinforce itself; they do not build any protein on their own."},{"id":"synthese-elevee","title":"3. Elevated protein synthesis","body":"Driven by those signals, the fibre assembles new proteins faster than it breaks them down. This is when the balance turns positive, and the signalling cluster is at its densest here."},{"id":"remodelage","title":"4. Remodelling","body":"The new proteins are built into the existing contractile structures. The muscle does not swell all at once: it reorganises itself, and signalling activity subsides."},{"id":"nouvelle-taille","title":"5. New fibre size","body":"When this cycle repeats regularly, the cross-section of the fibre eventually increases. The visible result is the sum of many tiny adaptations, never the product of a single session."}],"license":"Shapier — Propriétaire — usage interne ShapierLab"}},{"id":"b16","type":"callout","tone":"limit","title":"What the video simplifies","content":[[{"kind":"text","value":"The 3D model does not represent any particular person's anatomy: its proportions are chosen to make the sarcomeres visible, not to be exact."}],[{"kind":"text","value":"The animation leaves out satellite cells, the role of connective tissue, and the neural adaptations that account for part of the strength gained without any change in size."}]]},{"id":"b17","type":"sourceList","title":"Sources for this video","referenceIds":["schoenfeld2010","schoenfeld2017volume","morton2018","atherton2012"]},{"id":"b18","type":"relatedContent","title":"Read next","targetIds":["en-mechanism-how-muscle-grows","en-mechanism-tension-fatigue-volume","en-pathway-muscle-growth-path"]},{"id":"b19","type":"shapierAction","actionId":"exercises-squat","label":"See the squat page in Shapier","description":"Find the squat page in Shapier, an exercise that works the quadriceps, to see how to perform it and fit it into the week's training.","webTarget":"https://shapier.app/en/exercises/squat","appTarget":"shapier://exercises/squat"}],"relations":[{"type":"explains","targetId":"en-mechanism-how-muscle-grows"},{"type":"next-step","targetId":"en-mechanism-tension-fatigue-volume"},{"type":"shapier-action","targetId":"exercises-by-muscle"}],"authors":["equipe-editoriale-shapier"],"reviewers":["Thanh Chau"],"references":[{"id":"schoenfeld2010","authors":"Schoenfeld BJ","year":2010,"title":"The mechanisms of muscle hypertrophy and their application to resistance training","source":"Journal of Strength and Conditioning Research","kind":"review","doi":"10.1519/jsc.0b013e3181e840f3"},{"id":"schoenfeld2017volume","authors":"Schoenfeld BJ, Ogborn D, Krieger JW","year":2017,"title":"Dose-response relationship between weekly resistance training volume and increases in muscle mass: A systematic review and meta-analysis","source":"Journal of Sports Sciences","kind":"meta-analysis","doi":"10.1080/02640414.2016.1210197"},{"id":"morton2018","authors":"Morton RW, Murphy KT, McKellar SR, Schoenfeld BJ, Henselmans M, Helms E, Aragon AA, Devries MC, Banfield L, Krieger JW, Phillips SM","year":2018,"title":"A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults","source":"British Journal of Sports Medicine","kind":"meta-analysis","doi":"10.1136/bjsports-2017-097608"},{"id":"atherton2012","authors":"Atherton PJ, Smith K","year":2012,"title":"Muscle protein synthesis in response to nutrition and exercise","source":"The Journal of Physiology","kind":"review","doi":"10.1113/jphysiol.2011.225003"}],"review":{"publishedAt":"2026-08-02","reviewedAt":"2026-08-02","reviewDueAt":"2027-08-02","evidenceLevel":"established"},"limitations":["The animation shows a single isolated fibre: it leaves out connective tissue, blood supply and satellite cells, which also take part in the adaptation.","The work cited was carried out mostly in healthy adults following supervised resistance training; it does not describe injury, illness or growth.","The relative share of the mechanisms proposed in the literature is still debated: the video presents a teaching model, not a demonstrated hierarchy."],"seo":{"title":"How muscle grows — the video explained step by step","description":"Video and text explanation of muscle growth: mechanical tension, cellular signalling, proteins added, training volume and the limits of the model.","canonicalPath":"/en/videos/how-muscle-grows","image":"/og/en/video-muscle-growth.png"},"app":{"offlineEligible":true},"version":1}