legwork vs nitty-gritty

legwork

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

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

nitty-gritty

noun
  • The core or essence of something; the gist. 

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