amplify vs gain strength

amplify

verb
  • To add content that is not present in the source text to the target text, usually to improve the fluency of the translation. 

  • To increase the amplitude of something, especially of an electric current. 

  • To render larger, more extended, or more intense. 

  • To enlarge by addition or commenting; to treat copiously by adding particulars, illustrations, etc.; to expand. 

gain strength

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