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".

Use the full interactive calculator below, or

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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?