run out of steam vs sag

run out of steam

verb
  • To run out of energy or motivation. 

sag

verb
  • To lose firmness, elasticity, vigor, or a thriving state; to sink; to droop; to flag; to bend; to yield, as the mind or spirits, under the pressure of care, trouble, doubt, or the like; to be unsettled or unbalanced. 

  • To cause to bend or give way; to load. 

  • To wear one's trousers so that their top is well below the waist. 

  • To pull down someone else's pants. 

  • To loiter in walking; to idle along; to drag or droop heavily. 

  • To sink, in the middle, by its weight or under applied pressure, below a horizontal line or plane. 

  • To lean, give way, or settle from a vertical position. 

noun
  • The state of sinking or bending; a droop. 

  • The difference in height or depth between the vertex and the rim of a curved surface, specifically used for optical elements such as a mirror or lens. 

  • The difference in elevation of a wire, cable, chain or rope suspended between two consecutive points. 

How often have the words run out of steam and sag occurred in a corpus of books? (source: Google Ngram Viewer )