forward roll vs somersault

forward roll

noun
  • A movement in which one's body is rolled forward, by putting the head on the ground and swinging the legs over the head. 

somersault

noun
  • Starting on one's feet, an instance of rotating one's body 360 degree while airborne or on the ground, with one's feet passing over one's head. 

verb
  • To perform a somersault. 

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