{"schemaVersion":1,"id":"en-video-aerobic","type":"video","pillar":"energy","locale":"en","translationGroupId":"video-aerobic","slugPath":"videos/lasting-energy","title":"Lasting energy — the video","shortTitle":"Lasting energy","summary":"An animation showing why ATP is recycled rather than stored, and how the share of carbohydrate and fat changes with intensity. The page repeats the content in text.","level":"intermediate","estimatedMinutes":8,"synonyms":["aerobic system","oxidation","mitochondrion","carbohydrate","fat","endurance"],"blocks":[{"id":"b1","type":"paragraph","content":[{"kind":"text","value":"The stores that fuel a sprint empty within tens of seconds. What takes over is slower, but its capacity is on another scale entirely — and that pathway never stops, not even during the sprint."}]},{"id":"b2","type":"videoLesson","videoId":"systeme-aerobie-video","title":"Where lasting energy comes from"},{"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 central shot is not a store but a loop, and that is deliberate. The hardest idea to get across on this subject is that ATP is barely stored at all: it is rebuilt continuously, as fast as it is spent."}]},{"id":"b5","type":"definition","term":"Oxidation","definition":"A reaction that removes electrons from a molecule. In muscle, oxidising a fuel means recovering its energy in usable form, gradually turning it into carbon dioxide and water.","alsoKnownAs":["cellular combustion"]},{"id":"b6","type":"paragraph","content":[{"kind":"text","value":"The "},{"kind":"link","value":"aerobic system","href":"/en/energy/the-aerobic-system","external":false},{"kind":"text","value":" keeps that recycling running, inside the mitochondria, by oxidising carbohydrate and fat with oxygen. It yields far more ATP per molecule of fuel than the fast pathways, but it yields it more slowly."}]},{"id":"b7","type":"evidence","level":"established","statement":"The aerobic system becomes the dominant source of ATP as soon as an effort passes a few tens of seconds.","detail":"Reviews of energy system interaction converge on this point, drawing on gas exchange and biopsies during maximal ergometer efforts. The exact timing of the shift varies with the estimation method and the protocol used.","referenceIds":["gastin2001","baker2010"]},{"id":"b8","type":"heading","level":2,"text":"Two fuels, a gradual shift","anchor":"two-fuels-a-gradual-shift"},{"id":"b9","type":"paragraph","content":[{"kind":"text","value":"At low intensity, fat supplies a large part of the energy. As intensity rises, the share of carbohydrate grows until it dominates. The reason is mechanical: making ATP from fat takes more oxygen and more steps, which caps the rate."}]},{"id":"b10","type":"paragraph","content":[{"kind":"text","value":"What the video insists on showing is that no pathway switches off. What changes with intensity is the relative contribution of each, never whether it is running."}]},{"id":"b11","type":"evidence","level":"probable","statement":"Carbohydrate availability limits performance in prolonged efforts of sustained intensity.","detail":"Reviews on carbohydrate for training describe a drop in pace associated with depletion of [glycogen](/en/energy/muscle-glycogen-and-water). The size of the effect depends on duration, intensity, food intake before the effort and training status.","referenceIds":["burke2011"]},{"id":"b12","type":"heading","level":2,"text":"A common confusion","anchor":"a-common-confusion"},{"id":"b13","type":"callout","tone":"caution","title":"Share of fat and total energy","content":[[{"kind":"text","value":"The share of fat is higher at low intensity. That is correct, and it says nothing about the total energy spent, which is lower at that intensity."}],[{"kind":"text","value":"The two ideas — proportion and quantity — are regularly conflated, and the confusion often serves as an argument. This page describes a mechanism; it prescribes no way of training."}]]},{"id":"b14","type":"heading","level":2,"text":"The related scene","anchor":"the-related-scene"},{"id":"b15","type":"scene3d","sceneId":"cycle-atp-pcr","title":"ATP–phosphocreatine cycle","intro":"The scene shows the same loop in three dimensions. The aerobic pathway is what feeds it continuously: ATP is not stored but recycled, and the aerobic system keeps the recycling running.","accessibility":{"textAlternative":"Circular diagram: a pale ring carries three stations linked by arrows running anticlockwise. At the top, ATP is drawn as a large adenosine sphere followed by three small phosphate spheres; at the bottom left, ADP carries only two of them and a detached phosphate floats alongside; at the bottom right, phosphocreatine hands over its phosphate and leaves a creatine sphere behind. To the right of the circle, six discs stacked on a spindle represent the phosphocreatine store: the four thick discs at the bottom are still available, the two thin discs at the top have already been used, and an arrow links the store to the resynthesis station. A small marker travels around the ring to follow the cycle. The volumes are symbolic: neither the shape nor the size of the molecules is depicted.","structures":[{"label":"ATP","description":"Adenosine triphosphate carries three phosphate groups. It is the form of energy a muscle fibre uses directly in order to contract.","href":"/en/energy/atp-and-phosphocreatine"},{"label":"ADP and free phosphate","description":"When ATP gives up a phosphate, ADP and a free phosphate are left behind and the energy of the bond becomes available. The cell then has to rebuild ATP.","href":"/en/energy/atp-and-phosphocreatine"},{"label":"Phosphocreatine","description":"Phosphocreatine stored in the muscle hands its phosphate to ADP, which rebuilds ATP almost immediately. What remains is creatine.","href":"/en/energy/atp-and-phosphocreatine"},{"label":"Phosphocreatine store","description":"The stack stands for a limited store: the solid discs are still available, the pale ones have already been used. It is rebuilt during recovery.","href":"/en/energy/atp-and-phosphocreatine"},{"label":"Creatine","description":"Once its phosphate has been handed over, creatine is what remains. It is phosphorylated again when the effort stops and energy becomes available.","href":"/en/energy/atp-and-phosphocreatine"}],"steps":[{"id":"boucle","title":"1. A loop, not a line","body":"Cellular energy runs in a closed loop: ATP is spent, then rebuilt. A muscle stores almost no ATP in advance; it recycles it continuously."},{"id":"atp","title":"2. ATP, the energy currency","body":"ATP carries three phosphates, shown here as three small spheres in a row. It is the only form of energy the contractile proteins can use directly."},{"id":"hydrolyse","title":"3. One phosphate is released","body":"By releasing its third phosphate, ATP becomes ADP and frees the energy that powers contraction. The detached phosphate stays available inside the cell."},{"id":"resynthese","title":"4. Phosphocreatine recharges ATP","body":"Phosphocreatine transfers its phosphate to ADP: ATP is rebuilt almost instantly, without oxygen. It is the fastest route a muscle has."},{"id":"reserve","title":"5. A short-lived store","body":"The stack of discs stands for the phosphocreatine store: it supports a very short, very intense effort, then runs down. It is rebuilt during recovery, once the other pathways take over."}],"license":"Shapier — Propriétaire — usage interne ShapierLab"}},{"id":"b16","type":"heading","level":2,"text":"Sources","anchor":"sources"},{"id":"b17","type":"sourceList","title":"Main sources","referenceIds":["gastin2001","baker2010","burke2011"]},{"id":"b18","type":"shapierAction","actionId":"foods-carbohydrate-source","label":"See a carbohydrate source in Shapier","description":"Open the Shapier sheet for a common carbohydrate source.","webTarget":"https://shapier.app/en/foods/oats","appTarget":"shapier://foods/oats"},{"id":"b19","type":"quiz","title":"Check my understanding","questions":[{"id":"q1","prompt":"What is known about ATP storage in muscle?","choices":[{"id":"q1c1","label":"It is minimal: ATP is rebuilt continuously, as fast as it is spent","correct":true,"explanation":"This is the video's central idea: the central shot shows a loop, not a store."},{"id":"q1c2","label":"It is stored in large reserves that empty during exercise","correct":false,"explanation":"The stores that fuel a sprint do empty within tens of seconds, but the page states that ATP itself is barely stored at all."},{"id":"q1c3","label":"It is stored inside the mitochondria between efforts","correct":false,"explanation":"The mitochondria are where oxidation rebuilds ATP, not a storage site: the recycling runs continuously."}]},{"id":"q2","prompt":"As exercise intensity rises, what happens to the energy pathways?","choices":[{"id":"q2c1","label":"They all keep running: only their relative contribution changes","correct":true,"explanation":"The page insists on this point: no pathway switches off; what changes is each one's share."},{"id":"q2c2","label":"The fat pathway stops once carbohydrate becomes dominant","correct":false,"explanation":"Carbohydrate does become dominant at high intensity, but dominance is not shutdown: fat keeps contributing."},{"id":"q2c3","label":"The aerobic system only starts after a few tens of seconds","correct":false,"explanation":"That is when it becomes the dominant source of ATP, but it was already running: this pathway never stops, even during a sprint."}]},{"id":"q3","prompt":"The share of fat is higher at low intensity: which conclusion is correct?","choices":[{"id":"q3c1","label":"None about total energy: total expenditure is lower at low intensity, and proportion and quantity are different things","correct":true,"explanation":"This is exactly the confusion the page flags: a higher share says nothing about the total amount spent."},{"id":"q3c2","label":"More fat is burned in absolute terms at low intensity","correct":false,"explanation":"That is the classic conflation of proportion and quantity: the share of fat is higher but the total energy spent is lower at that intensity."},{"id":"q3c3","label":"The share of carbohydrate also rises at low intensity","correct":false,"explanation":"It is the opposite: as intensity rises, the share of carbohydrate grows until it dominates."}]}]},{"id":"b20","type":"relatedContent","title":"Read next","targetIds":["en-mechanism-aerobic-system","en-mechanism-hydration","en-pathway-nutrition-path"]}],"relations":[{"type":"explains","targetId":"en-mechanism-aerobic-system"},{"type":"prerequisite","targetId":"en-mechanism-atp-phosphocreatine"},{"type":"next-step","targetId":"en-mechanism-hydration"},{"type":"shapier-action","targetId":"nutrition-carbs"}],"authors":["equipe-editoriale-shapier"],"reviewers":["Thanh Chau"],"references":[{"id":"gastin2001","authors":"Gastin PB","year":2001,"title":"Energy system interaction and relative contribution during maximal exercise","source":"Sports Medicine","kind":"review","doi":"10.2165/00007256-200131100-00003"},{"id":"baker2010","authors":"Baker JS, McCormick MC, Robergs RA","year":2010,"title":"Interaction among skeletal muscle metabolic energy systems during intense exercise","source":"Journal of Nutrition and Metabolism","kind":"review","doi":"10.1155/2010/905612"},{"id":"burke2011","authors":"Burke LM, Hawley JA, Wong SHS, Jeukendrup AE","year":2011,"title":"Carbohydrates for training and competition","source":"Journal of Sports Sciences","kind":"review","doi":"10.1080/02640414.2011.585473"}],"review":{"publishedAt":"2026-08-02","reviewedAt":"2026-08-02","reviewDueAt":"2027-08-02","evidenceLevel":"established"},"limitations":["The bars comparing fat and carbohydrate convey a trend, not a measurement: the real proportion depends on intensity, duration, recent food intake and training.","The available measurements rely on gas exchange and biopsies taken in laboratories, on small numbers of people, under conditions more controlled than real training.","The video describes a general mechanism: it assesses no one's fitness and proposes no diet."],"seo":{"title":"Lasting energy — the video on the aerobic system","description":"Video and text explanation: why ATP is recycled rather than stored, what the mitochondrion oxidises, and how intensity changes the share of each fuel.","canonicalPath":"/en/videos/lasting-energy","image":"/og/en/video-aerobic.png"},"app":{"offlineEligible":true},"version":1}