I find that terminology confusing, too. But one image that has helped me is to visualize an accordian fold. The upper body is one pleat, a fold at the hips so that from the hip to the knee is another pleat, then knee to heel is the third pleat. In jumping, the lower leg stays move still, but there are times when it might change, and even in posting you are not only changing the hip angle by opening that "fold", you are also openning the fold of the knee, too.
Accordian closer, accordian further apart. That openning of the fold at the hip joint can happen by EITHER you straightening your upper body to a more vertical stature, OR you bringing your knee more directly underneath you , and thus your heel further back (in the saddle). Both motions open the angle of that "fold".
Last edited by tinyliny; 03-21-2011 at 02:22 AM.