get one's ass in gear vs undertake

get one's ass in gear

verb
  • To exert effective effort; to get going; to get moving; to start producing. 

undertake

verb
  • To take upon oneself; to start, to embark on (a specific task etc.). 

  • To commit oneself (to an obligation, activity etc.). 

  • To pass a slower moving vehicle on the curbside rather than on the side closest to oncoming traffic. 

noun
  • The passing of slower traffic on the curbside rather than on the side closest to oncoming traffic. 

How often have the words get one's ass in gear and undertake occurred in a corpus of books? (source: Google Ngram Viewer )