I think the key to understanding _mobilization_ in this context is in the second sentence:
> [Glycogen] can be broken down to yield glucose molecules **when energy is needed**.
The authors are using _mobilize_ in a figurative sense to suggest that glycogen can be quickly and efficiently metabolized to suit the energy needs of the body, like an army may be _mobilized_ to fight a war. See definition #2 on Wiktionary:
> **mobilize** (verb)
> 2\. ( _transitive_ ) To assemble troops and their equipment in a coordinated fashion so as to be ready for war.