1
general::
Seize an opportunity; begin at full speed. For example, As soon as the front office gave its approval for the new department, we hit the ground running. The origin of this term is disputed. It may come from troops dropped into a combat zone, from stowaways jumping off a freight train as it nears the station, or from Pony Express riders avoiding delay when they changed mounts.
American Heritage Idioms
2
general::
Phrase(s): hit the ground running
Fig. to start the day very energetically. • A decade ago I had a lot more energy. I would wake up, hit the ground running, and never stop until I went to bed again.
McGrawhill's American Idioms And Phrasal Verbs