fitness center vs gymnasium

fitness center

noun
  • A gym or fitness club. 

gymnasium

noun
  • A large room or building for indoor sports. 

  • A type of secondary school in some European countries which typically prepares students for university. 

  • A public place or building where Ancient Greek youths took exercise, with running and wrestling grounds, baths, and halls for conversation. 

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