Sometimes, in order to make a model flow correctly, you have to totally ignore the current flow of fibers and cross sections, and redirect them. I had to do this for the pectoral muscles. The yellow line shows where I made cuts, and then welded vertices, and drew new lines in order to accomadate this new definition.

Right: Here I added even more lines, and really made the chest read as a chest instead of a rough shape extruded out, which is what many people try to do with their muscles.
If you don't know what it looks like under the skin, if you dont know how it inserts, and where, then do not try to do a model that has defined muscles. Period.
Do not attempt to make up muscles either, and claim that it is an Alien or a Monster, and it doesnt matter because the muscles are made up.

You have to know correct anatomy before you can make up your own. This is where life drawing sessions are key.

Note from 3DTotal: It is helpful to get a book on anatomy for artists!

In this step, I started defining the buttox, and lower back muscles. Notice how I am disreguarding where the current lines lie, and will redraw, or remove existing lines in order to help make the correct flow.

Right: In order to define a muscle, or any feature for that matter, you have have to set its outline, or valley.

The yellow lines are the "valley". then you have to draw the actual definition lines, or Peaks.
The red lines are the "peaks".

The valley's make it so that when you bring out the peaks, and then scale them , the definition is limited to within the valley lines.

Many times, people will draw peaks, but not valleys, then when they scale the peaks, there is nothign to contain their definition, so the muscles end up wonky (wonky is an official term, coined by my great drawing 2 teacher).

So much about the body, let's move on to the head, a complex terrain to work in...