fatigue vs strengthen

fatigue

verb
  • To tire or make weary by physical or mental exertion. 

  • To lose so much strength or energy that one becomes tired, weary, feeble or exhausted. 

  • To cause to undergo the process of fatigue. 

  • To wilt a salad by dressing or tossing it. 

  • To undergo the process of fatigue; to fail as a result of fatigue. 

noun
  • Weakening and eventual failure of material, typically by cracking leading to complete separation, caused by repeated application of mechanical stress to the material. 

  • A weariness caused by exertion; exhaustion. 

  • A menial task or tasks, especially in the military. 

strengthen

verb
  • To make strong or stronger; to add strength to; to increase the strength of; to fortify. 

  • To empower; to give moral strength to; to encourage; to enhearten. 

  • To reinforce, to add to, to support (someone or something) 

  • To grow strong or stronger. 

  • To substantiate; to corroborate (a belief, argument, etc.) 

  • To augment; to improve; to intensify. 

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