invigorate vs pep up

invigorate

verb
  • To make lively. 

  • To impart vigor, strength, or vitality to. 

  • To heighten or intensify. 

  • To give life or energy to. 

pep up

verb
  • To make stronger or more interesting. 

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