Glycogen Depletion 101

From Running tips for everyone from beginners to racing marathons and ultramarathons

Notes on Glycogen Depletion

The body's carbohydrate stores are limited. Carbohydrate is stored as Glycogen in the muscles and the liver. ^[1]
Some carbohydrate is needed to fuel the body and mind. Lack of carbohydrate will reduce the performance of both the body and the mind.
The harder you run (higher percentage of aerobic capacity), the more of the body's fuel comes from carbohydrate and the less from fat. ^[2]
You can consume carbohydrate when you run to augment your glycogen stores. ^[3]
The harder you run, the harder it is to digest; there is a limited amount of blood, and if it is all in use by the muscles, there is none left for the digestive system.
In endurance running, glycogen is depleted from slow twitch (endurance) muscle first. ^[4]
Most Gels are very easily digested. See The Science of Energy Gels and Comparison of Energy Gels.
Training can reduce glycogen depletion in several ways
- Endurance training can teach the body to prefer fat as a fuel source and spare carbohydrate^[5]
- Training increases the amount of glycogen stored in the muscles^[6]
- Training can improve efficiency, so that you need less energy to cover the distance.
Caffeine has been shown to increase the percentage of fat used for fuel.
Higher body weight requires more energy per mile. However, the body's supply of glycogen is dependent on the liver and muscles, which may not be proportionately large.

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