weaken vs work up

weaken

verb
  • To become weaker or less strong. 

  • To make weaker or less strong. 

work up

verb
  • To develop. 

  • To raise; to excite; to stir up. 

  • To give (a patient) a general medical examination to assess health and fitness. 

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