on foot vs shifting

on foot

prep
  • In progress or in preparation; active, in operation. 

  • On one's feet; walking, jogging or running but not in a vehicle or on the back of an animal. 

shifting

noun
  • The phenomenon by which two or more constituents appearing on the same side of their common head exchange positions to obtain non-canonical order. 

  • A shift or change; a shifting movement. 

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