One of your main muscles in the torso is the rectus abdominus.(also known as your abs) the rectus abdominis is a flat long muscle that extends the entire length or abdomen.  the muscle has a shealth that helps it hold its postion but doesnt keep the flexiablity away from the muscles moving.  the outside abs of your body are called exterinal abdominal oblique.  the oblique help us by one side bends the vertebral column sidewaysb and can rotate it bringing the shoulder of that side forward.  when the shoulder goes forward the other shoulder is rotated backwards.  The oblique is an very important contribute to our musular system. these are the two most important muscles in the abdomine muscles.