clonus vs stiffness

clonus

noun
  • A muscular spasm with regular contractions. 

stiffness

noun
  • muscular tension due to unaccustomed or excessive exercise or work; soreness. 

  • inelegance; a lack of relaxedness. 

  • rigidity or a measure of rigidity. 

  • inflexibility or a measure of inflexibility. 

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