limber up vs undertake

limber up

verb
  • To prepare; to make oneself ready. 

  • To stretch one's muscles to make them more limber, usually as a preparation for physical exercise. 

  • To make (someone or something) more limber or flexible. 

  • To attach a limber. 

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 limber up and undertake occurred in a corpus of books? (source: Google Ngram Viewer )