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8 min read

Glycogen and weight swings — the video

An animation that explains why the number on a scale moves by several hundred grams from one day to the next: muscle glycogen is stored along with water, and that water changes in quantity far faster than tissue does.
3D scene
Storing and using glycogen
The scene takes the glycogen granules shown in the video and lets you explore them step by step: a full store, mobilisation during effort, rebuilding after food is taken in. Every step is described in text below the scene and stays understandable without displaying the model.
Open in the explorer
A scale can show several hundred grams of difference between two mornings without anything notable having happened. The video explains where that swing comes from, and why it is mostly about water bound to an energy store.

Glycogen and weight swings

Duration: 1:24

Chapters

  • 0:00
    Stored fuel
  • 0:14
    Depletion and refill
  • 0:38
    The water that comes with it
  • 1:02
    Reading the scale
Transcript
Glycogen is the form in which the body stores carbohydrate in muscle and liver. It is the main store mobilised during intense, prolonged effort.
Effort lowers the muscle store, which carbohydrate intake then rebuilds. Refill speed depends on the amount of carbohydrate supplied and the delay after effort. A low store is felt mostly on long or repeated efforts.
Glycogen is stored together with water: the two vary together. That is why scale weight can move by several hundred grams within a single day. That variation tells you nothing about fat mass or muscle mass.
A single measurement mixes glycogen, water, digestive content and real mass. Only the trend observed across several weeks says anything about body composition. Understanding this variation avoids drawing hasty conclusions from one morning number.

What the video shows

The animation starts from a muscle fibre and zooms in on small branched clusters scattered between the contractile filaments: granules of glycogen. Each granule is a chain of glucose molecules hooked to one another, ready to be taken apart.
The next shot is the heart of the video. Water molecules appear around every granule, drawn in blue. They are not decoration: glycogen is stored in a hydrated environment, and how much of it there is partly determines how much water is held in the muscle. When the animation dismantles the granules during a long effort, the water that went with them leaves too.
The final sequence puts a scale under the silhouette. The reading falls during the effort, then climbs back after a carbohydrate-rich meal, even though no fat has been lost or gained in between. The video closes on that contrast: a scale measures a total mass, not what it is made of.
Muscle glycogen
A store of glucose held inside the muscle, used mainly by that muscle during effort. It runs down with prolonged work and is rebuilt from the carbohydrate taken in from food.
carbohydrate store · muscle glucose store

Why weight moves so fast

Glycogen does not weigh anything on its own. It is that partnership between the store and its water that makes the morning number unstable, while tissue itself changes slowly.
Certainty level · Probable
Storing muscle glycogen goes together with water being held in the muscle, which makes body mass vary independently of any change in tissue.
A study in trained men, after prolonged exercise performed in the heat, tracked glycogen rebuilding and muscle water content in parallel, and reports an order of magnitude of roughly three grams of water stored per gram of glycogen. The sample is small, the experimental conditions are particular and other work debates that ratio: it should be read as an order of magnitude, not as a constant.
Fernández-Elías VE, Ortega JF, Nelson RK, Mora-Rodriguez R (2015)

Emptying and refilling the store

The video shows the store running down during a long effort, then being rebuilt. That coming and going is what glycogen normally does, not a malfunction.
Two points do not appear on screen. First: muscle glycogen serves the muscle that holds it, whereas the store kept in the liver plays a different role, keeping glucose available to the body as a whole. Second: how fast the store is rebuilt depends on the time left between two efforts as much as on the amount of carbohydrate taken in. The animation condenses all of that into a single cycle to stay legible.
Certainty level · Established
Carbohydrate availability determines how muscle glycogen stores are rebuilt between two efforts.
Reviews of carbohydrate for training describe rebuilding as proportional to carbohydrate intake and to the time available, and express their reference figures in grams per kilogram of body mass rather than in absolute values, adjusted to the training load. Those reference figures are established for athletic populations studied as groups and are not an individual recommendation.
Burke LM, Hawley JA, Wong SHS, Jeukendrup AE (2011)

The linked scene

Storing and using glycogen

The scene takes the glycogen granules shown in the video and lets you explore them step by step: a full store, mobilisation during effort, rebuilding after food is taken in. Every step is described in text below the scene and stays understandable without displaying the model.
Current step
1. The store inside the fibre
On the left, a muscle fibre opened along its length. The dark spheres spread inside stand for glycogen granules, the form in which muscle stores carbohydrate.
Scene description
Comparative diagram: two identical muscle fibres, opened lengthwise like slices, sit side by side on pale plinths. The left one, with full stores, holds about ten dark spheres — the glycogen granules — each ringed by three small spheres standing for the water stored with it; above it, a six-segment gauge is completely filled. The right one, with low stores, holds only three granules and their water, and its gauge shows just two solid segments followed by four hollow ones. Between the two fibres, an upper arrow pointing right represents the effort that empties the store, and a lower arrow pointing left represents the dietary refuelling that rebuilds it. Sizes and counts are symbolic: nothing here is to scale.
Visible structures
  • Glycogen granule
    Glycogen is the form in which muscle stores carbohydrate. It is gathered into granules spread through the fibre, ready to be mobilised quickly during effort.
  • Associated water
    Glycogen is stored together with water, shown here as the small satellite spheres. When the store falls, that water leaves with it and the number on the scale follows, which says nothing about fat mass.
  • Fibre in section
    The fibre is drawn as a slice, as if it had been opened along its length. The section only serves to show what it contains.
  • Low stores
    After a long effort, few granules are left. The fibre still works, but the intensity it can sustain drops.
  • Refuelling
    Dietary carbohydrate rebuilds glycogen, and the associated water comes back with it. This is one of the reasons the number on the scale moves from one day to the next.
Guided steps
  • 1/5
    On the left, a muscle fibre opened along its length. The dark spheres spread inside stand for glycogen granules, the form in which muscle stores carbohydrate.
  • 2/5
    Each granule is ringed by small spheres: the water stored alongside it. Glycogen and water travel together, which explains part of the day-to-day swings on the scale.
  • 3/5
    During sustained effort the fibre breaks down its glycogen to produce energy. The upper arrow shows the move from one state to the other, and the group of granules shrinks.
  • 4/5
    On the right, the same fibre after the effort: few granules, little associated water, an almost empty gauge. The number on the scale has dropped, but that particular drop comes from glycogen and its water, not from fat mass.
  • 5/5
    Dietary carbohydrate rebuilds the store and the water returns with it: the lower arrow brings the fibre back to its full state. This back-and-forth repeats continuously, independently of fat mass.
Model licence · Shapier — Propriétaire — usage interne ShapierLab
Caution
What this page does not say
This page explains a storage mechanism. It gives no amount of carbohydrate to eat, proposes no diet and allows nobody's weight to be interpreted.
An unexplained, rapid or persistent change in weight is a matter for a healthcare professional who can examine the person concerned.

Sources for this video

  • Burke LM, Hawley JA, Wong SHS, Jeukendrup AE (2011). Carbohydrates for training and competition. Journal of Sports Sciences.
  • Fernández-Elías VE, Ortega JF, Nelson RK, Mora-Rodriguez R (2015). Relationship between muscle water and glycogen recovery after prolonged exercise in the heat in humans. European Journal of Applied Physiology.

Check my understanding

What does the scale mostly measure when it shows several hundred grams of difference between two mornings?
What should be remembered about the figure of roughly three grams of water per gram of glycogen?
How does the page tell apart the glycogen held in muscle and the store kept in the liver?
Choose an answer

Read next

  • Muscle glycogen and water
    Why can the number on the scales change within two days without any change in fat mass? This page explains what muscle glycogen is, its role as a fuel and the water that accompanies it inside the muscle.
    With a 3D scene
  • ATP and phosphocreatine
    Where does the energy for the very first seconds of a maximal effort come from? This page describes the energy currency of muscle, the buffering role of phosphocreatine, and why the energy systems do not take turns the way they are usually described.
    With a 3D scene
  • Energy and recovery
    A six-step reading pathway that follows muscle energy from the second to the night: the instant recharge of ATP, the glycogen stores and their water, then the role of sleep. A closing quiz lets you check what you have taken in.
    Described without a scene
Put it into practice in Shapier

Explore nutrition around training in Shapier

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Explore nutrition around training in Shapier
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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 ratio between water and glycogen was measured in small groups of trained adults, after prolonged exercise in the heat: it does not transfer as it stands to every situation.
  • The number shown by a scale also depends on gut contents, on overall hydration and on other factors this page does not cover.
  • None of the data cited makes it possible to interpret one person's weight change or to draw any dietary conclusion from it.
Sources
  • Burke LM, Hawley JA, Wong SHS, Jeukendrup AE (2011). Carbohydrates for training and competition. Journal of Sports Sciences.
  • Fernández-Elías VE, Ortega JF, Nelson RK, Mora-Rodriguez R (2015). Relationship between muscle water and glycogen recovery after prolonged exercise in the heat in humans. European Journal of Applied Physiology.
Educational content. Body Lab does not diagnose and does not replace professional advice.
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