I'm not clear which version of Poser Pro you have since the term was used since version 4. However before purchasing new content, suggest that you load the SimonG2 figure, select its BODY and set the Mesomorph dial to 1.000 and see if that suits your purpose.

If your version does not have that figure then look through the figure library and try others. Many of the Poser figures include some form of muscular morph.