The Collaborative International Dictionary of English v.0.48:

Muscularity \Mus`cu*lar"i*ty\, n.
   The state or quality of being muscular. --Grew.
   [1913 Webster]

WordNet (r) 3.0 (2006):

muscularity
    n 1: the physiological state of having or consisting of muscle
    2: possessing muscular strength [syn: brawn, brawniness,
       muscle, muscularity, sinew, heftiness]
    3: an imaginative lively style (especially style of writing);
       "his writing conveys great energy"; "a remarkable muscularity
       of style" [syn: energy, muscularity, vigor, vigour,
       vim]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "muscularity":
   beef, beefiness, brawn, brawniness, elasticity, heftiness,
   huskiness, involuntary muscle, muscle, musculature, physique,
   sinew, sinewiness, sinews, thew, thewiness, thews, tone,
   voluntary muscle