constrain vs encumber

constrain

verb
  • To force physically, by strong persuasion or pressuring; to compel; to oblige. 

  • To keep within close bounds; to confine. 

  • To reduce a result in response to limited resources. 

encumber

verb
  • To restrict or block something with a hindrance or impediment. 

  • To burden with a legal claim or other obligation. 

  • To load down something with a burden. 

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