legwork vs spadework

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. 

spadework

noun
  • Work done in preparation for something else. 

  • Work done by digging with a spade. 

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