To re-energize yourself before losing any initial energy or
vigor you had
beforehand. Energizing yourself (e.g. through coffee or
Red Bull) once already tired would be rejuvenating, but doing so before the crash eliminates the "re" and is simply juvenating.
girl #1: Hey, you look excited today... did something happen?
girl #2: Well, I am excited for the concert I'm going to tonight plus I just finished a
cappuccino double shot which has kept me juvenated.