Like some others, I'm not satisfied with "armor pieces" making up torso musculature. This is especially because I discovered that you can make surprisingly good musculature with creature limbs. So, I decided to try something a little more out of the box.
Here's a creature where I tested out a torso similar in concept to MadMaxRW:
Buffosaur:
http://www.spore.com/sporepedia#qry=srch- buffosaur%3Asast-500002051367
Youtube Vid:
http://www.youtube.com/watch? v=xVjz2u2FWAo
Like MadMax, I used limb segments for the pecs, but unlike his Hell Knight creature I also used them to create a six-pack of a sorts, too. The obvious pro is that it looks incredibly muscular (oh geebus!! :O ), but the con for the Buffosaur is that it looks very floppy for half of his movements. This is especially noticeable up close. But like MadMax said, I believe there are certain limbs, sizes, and configurations one can use to reduce the floppy factor (and not make man boobs

)...um...I just didn't use the right ones. It really takes some playing around, as he said. I might mess with the Buffosaur again to fix this issue.
Also, Buffosaur's tail and legs could use work.
What I did:
After playing with different arms and blowing up their size just for fun, I realized that some of them actually showed musculature. So for whatever reason from there, I decided to make a muscular creature (since I haven't seen anyone do it) and see what would happen if I made the attempt.
This took me about one hour of fiddling and experimenting. I used burly arms for Buffosaur and modified them. What I mean by this is that I used the "upper arm" segment of the burly arm for both the upper arm and forearms of the creature, which surprisingly shows even more musculature just fine. Depending on how well you shape the arm and the upper torso and neck, you can also create deltoid and trapzius muscles in the process.
For the legs I used Callypigeon and also modified them like the Burly arms above to a degree.
In other words, for those of you who don't know it, you can use CTRL + drag to take apart certain limb segments. If you so desire, you can add many more joints to a limb or even use different parts from other limbs to create your own unique pair of limbs. You aren't limited to what is on the menu.
For his abdominal musculature, I used ALT + drag to copy the pectorals, then shrunk them.
How I "hid" the "torso limbs" in the editor:
Okay, what I did was take apart a limb until one limb segment with two blue spheres remained. Now the challenge is to hide one of the spheres in the body (somehow) so they don't look like limb segments but rather, um, muscles.
MadMaxRX's out-of-the-box solution was to not totally hide one side of the limb segments, but to use them as part of the neck muscles. If you download his creature and put it in the editor, you'll see what I mean.
My solution is actually a bug in nature (at least, I'm quite sure it is). I was messing around with one of the blue spheres of the limb segment, moving it around, and then it finally disappeared into the body completely. In test drive mode the limbs never pop out or do anything strange. Success!
http://i4.photobucket. com/albums/y108/Sagey2/buffosaurarm.jpg
The above picture shows the general area where I hid the shrunken blue sphere and it magically "disappeared." When it disappears, it doesn't show up in the build editor unless you move the entire limb around. I believe this happened because the creature's arms are so, well, thick. However, this did take me a bit of playing around to figure it out.
The reason why I used the arm areas to hide the little sphere was because the limbs look more elongated sideways on the chest rather than spherical...if they're too spherical they turn into breasts, and, well...that is a bit too inappropriate I guess.
In Conclusion:
Buffosaur's torso musculature is too floppy, but I believe with the right sizes/combinations/whatever, someone can make (sorta) realistic musculature that doesn't impede on the creature very much. So I think it is possible. I know Buffosaur is way too muscular for many people (he is for me), but this can probably be done in a smaller size. Since I've seen this thread I guess I might try that. Gotta finish this weird spider creature I'm trying to make, though.