Opposite words for supple:
heavy, slow, breakable, inelastic, stiffened, flaky, compact, unyielding, crisp, quiescent, indolent, dull, nonelastic, firm, crumbly, inert, brittle, solid, lazy, stupid, nonmalleable, sluggish, hard, awkward, short, friable, rigid, stiff, quiet, inflexible, idle, inactive, fragile.
Usage samples:
  1. In another second the terrible tension will be relaxed and that supple black body will launch itself at the sleeping man.
    "In the Musgrave Ranges", Jim Bushman.
  2. The former were of that same lithe, supple- bodied, straight- featured type which the wonderful art of the latter has enthroned, for all the ages, as the noblest realization of ideal physical beauty.
    "Roman Women Woman: In All Ages and in All Countries, Volume 2 (of 10)", Alfred Brittain.
  3. 899, on the L. wall, A Hunting Picnic, is an admirable specimen of his supple talent.
    "The Story of Paris", Thomas Okey.
  4. He looked down at his supple white fingers and shivered.
    "The Valiants of Virginia", Hallie Erminie Rives.