abstain vs exert

abstain

verb
  • Refrain from (something or doing something); keep from doing, especially an indulgence. 

  • Deliberately refrain from casting one's vote at a meeting where one is present. 

exert

verb
  • To put in vigorous action. 

  • To make use of, to apply, especially of something non-material. 

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