WordNet (r) 3.0 (2006):

limber up
    v 1: attach the limber; "limber a cannon" [syn: limber,
         limber up]
    2: make one's body limber or suppler by stretching, as if to
       prepare for strenuous physical activity [syn: limber up,
       warm up, loosen up]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "limber up":
   cushion, ease, fluff, gentle, get ready, get set, knead, laxate,
   limber, loosen, mash, massage, mellow, milden, mollify, plump,
   pulp, relax, shake up, shoulder arms, smash, soften, soften up,
   squash, strip for action, subdue, supple, tenderize, tone down,
   tune down, warm up, whet the knife