Originally Posted by Drew Eckhardt

Most of that is in your muscles - about 400 grams and 1600 Calories. Half a normal person's muscle mass is in their upper body, so only 800 Calories of that is accessible to your legs.

Some of cyclist's leg muscles get sore when we walk or run moderate distances, suggesting those muscle fibers and their stored glycogen don't get used riding.

These numbers are also averages. Training increases glycogen storage capacity. Diet also affects it

Effect of exercise-diet manipulation on muscle glycogen and its subsequent utilization during performance.

The liver adds another 100g/400 Calories and blood 25g/100 for maybe 1300 you can actually use.