keep fit vs slimnastics

keep fit

noun
  • exercises designed to promote physical fitness if performed regularly. 

  • Organised group aerobics class 

verb
  • To exercise for physical fitness. 

slimnastics

noun
  • A form of athletic exercise intended to promote weight loss. 

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