The Collaborative International Dictionary of English v.0.48:

Muscling \Mus"cling\, n. (Fine Arts)
   Exhibition or representation of the muscles. [R.]
   [1913 Webster]

         A good piece, the painters say, must have good
         muscling, as well as coloring and drapery.
                                                  --Shaftesbury.
   [1913 Webster]