Arching and Flexing

verb

• Form an arch or curve.
  • usage: "her back arches"; "her hips curve nicely"
  • synonyms: arch, curve, arc

adjective

• Forming or resembling an arch.
  • usage: "an arched ceiling"
  • synonyms: arced, arched, arciform, arcuate, bowed

• (p.pr.&vb.n.) of Arch.
• (n.) Hogging; -- opposed to sagging.
• (n.) The arched part of a structure.