How much glycogen is stored in the body?

The average person stores approximately 400-500 g of glycogen: 300-400 g in muscle, 75-100 g in the liver. At 4 kcal/g, this represents 1,600-2,000 kcal of carbohydrate fuel.

At what exercise intensity is glycogen the primary fuel?

Above ~65-70% VO2max, glycogen becomes the primary fuel. At race intensity for a 3-hour marathon (~80% VO2max), glycogen is nearly the sole fuel and stores are depleted in approximately 2 hours without supplementation.

What happens when glycogen runs out?

Glycogen depletion ("bonking" or "hitting the wall") causes a sudden, dramatic performance decrease, muscle weakness, cognitive impairment, and often overwhelming fatigue. Athletes must slow pace dramatically or stop.

Glycogen Depletion Time Calculator

Estimate time to glycogen depletion at a given exercise intensity and running or cycling speed, to plan fueling strategy and prevent the performance cliff known as "hitting the wall".

Core Tools

Distance covered in 12 minutes (meters)

🏅 Sports Note: These calculators provide estimates based on population data and validated formulas. Individual results vary by physiology, training level, and testing conditions. Consult a qualified coach or sports scientist for personalized guidance.

How to Use

Enter the values for the scenario you are assessing. Estimate time to glycogen depletion at a given exercise intensity and running or cycling speed, to plan fueling strategy and prevent the performance cliff known as "hitting the wall". Use the glycogen depletion result to inform your calculation.

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Glycogen Depletion Time Calculator

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Frequently Asked Questions

How much glycogen is stored in the body?

At what exercise intensity is glycogen the primary fuel?

What happens when glycogen runs out?