"Lines" within the Torso

As shown in the drawings, the torso has "lines" in it formed by the bones within.  In profile, these landmarks show up as diagonals.  By stretching or compressing these lines while using the spine as a hinge can help you draw the torso bending forward or back.  You can remember these lines by thinking they look like "Pac-Man's mouth."

In contrast to the profile, the torso when viewed from the front or back has landmarks that show up as parallel lines.  By compressing the lines to the left (as shown above), one can show the shift of the torso as the body moves into a contrapposto pose.

Keep these lines in mind when drawing the figure.  Drawing them in at the start of a sketch can help you capture natural-looking poses and actions.

from The Human Figure by John H. Vanderpoel