immobilize vs step up

immobilize

verb
  • To modify a surface such that things will not stick to it 

  • To tie up a capital: make a capital investment that makes that capital unavailable. 

  • To render motionless; to stop moving or stop from moving. 

step up

verb
  • To increase, augment, or advance, especially by one or more steps. 

  • To assume or take responsibility. 

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