backtrack vs go forward

backtrack

noun
  • the act of backtracking 

verb
  • To retrace one's steps. 

  • To exercise a racehorse around the racetrack in the opposite direction to that in which races are run. 

  • To taxi down an active runway in the opposite direction to that being used for takeoff. 

  • To repeat or review work already done. 

go forward

How often have the words backtrack and go forward occurred in a corpus of books? (source: Google Ngram Viewer )