Slow Motion Ballet

This is a great video to study. Watch it through at least once to see the entire sequence.  On the second viewing, use the pause button to pick out and sketch the best gestures that show a clear line of action, squash/stretch, and balance.

Contrapposto Skeleton

Here's a before-and-after illustration of what happens to the skeleton when the body shifts to a contrapposto pose.

from Human Anatomy by Jose M. Parramon

"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

Weight Emphasis

I especially like the small sketches at the bottom of the page.  They show what the body does to compensate when the torso leans away from the main line of balance.

from Body Parts by Simon Jennings