挺腰

挺腰	tǐng yāo	to straighten one's back / to arch one's back
挺	tǐng	straight / erect / to stick out (a part of the body) / to (physically) straighten up / to support / to withstand / outstanding / (coll.) quite / very / classifier for machine guns
腰	yāo	the waist and lower back / (bound form) kidney of an animal (as food) / the waist of trousers or a skirt / (metonym) money pouch; pocket / (bound form) the middle section of an upright object (mountain, bottle etc)