I think I know what you're talking about. I learned how to add a bit of "motion" and "dynamicism" in my artwork after taking some figure drawing classes, but here's the tidbit you need to really know: the line of motion.
The line of motion is what unites every figure to some degree. The more curvaceous or 'violent' the line is, the more dynamic the figure. A straight line would indicate a person standing perfectly still, or lying on the back perfectly straight. An sideways "U" could represent a person getting kicked in the stomach, where the most curved part being the person's stomach.
[First Drawing Here Shows Line of MotionAnyway, what I'm getting at with this "line of motion" business is that what you're looking for is the very subtle "S" shape. Imagine a very softly curving "S" like that of a person's spine. Then, start drawing in where the person's torso would be, the hips, etc. Indicate the direction of the shoulders as well as the direction of the hips with lines. Be aware of the weight shift in the human body.
If you want me to redline your image, tell me. I can explain better through pictures instead of words.
