well, as a first post, here's a pic of a mod in the game The Elder Scrolls: Oblivion. found it on bbwchan, thought that it looked pretty good. mostly my reason for posting this, though: someone PLEASE help me find this mod!!
 
http://yum.bbwchan.org/bbwart/src/1193857826618.jpg

will do. though i suspect that it will be difficult to find, if half an hour of google didn't turn up anything. i suspect that it may be a japanese mod, in which case i am totally at a loss of how to find it. in any case, this forum is so much nicer than the last one i posted this request in. because of some vague insult that i didn't even know i typed in, i got permanently banned for no good reason. anyway, will update if i find the mesh.

I have Nif tools myself, it's how I make sure the skin wraps around the body nicely.  Unfortunately, I don't have any 3d modelling software to actually modify the mesh.  Eshme's body mesh would be a good start but without 3d studio Max, Gimp, or maybe even Maya it won't be possible to make the characters more muscular.

Also keep in mind that if you download the muscle mod it is entirely possible that armor and other things that haven't been modified will shrink your character down into the default mesh until you remove the armor for which it will go back to it's muscle version size.

I have a copy of maya installed on my computer, Maya 8.0 Unlimited, but I don't have a serial key to activate the license.  So it's essentially installed but non functional, I would certainly see if it is possible to make muscle mesh in Maya but can't do anything without the key.