back down vs step forward

back down

verb
  • To withdraw from a commitment or position. 

  • To take a less aggressive position in a conflict than one previously has or has planned to. 

step forward

verb
  • to volunteer for something; to offer one's services 

  • to take one or more steps forward, especially in response to a request for identification 

  • to admit one's wrongdoing, to own up 

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