A trained cyclist stores approximately 400-500g of glycogen (1600-2000 kcal). At threshold intensity, glycogen is the dominant fuel. Below Zone 2, fat oxidation contributes more. In-ride fuelling (60-90g/hr carbohydrate) extends glycogen availability. The 'fuel for the work required' framework periodises carbohydrate intake: high carbs on hard days (glycogen-demanding), lower carbs on easy days (fat-oxidation focus).