legwork vs reconnaissance

legwork

noun
  • Work, especially research or preparation, that involves significant walking, travel, or similar effort. 

  • Skillful or vigorous use of the legs, as in dance or sports. 

reconnaissance

noun
  • The act of scouting or exploring (especially military or medical) to gain information. 

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