Stacked, Structurally Aligned stance.

Stacked, Structurally Aligned, Long & Strong outside leg.

Overly flexed stance.  Tires a skier quickly.

Also called Structurally Aligned, it's a stance in which the leg bones, and sometimes the spine, are aligned such that the forces of skiing that attempt to drive a skier's body into the snow are resisted by the compression strength of a skier's bones.  In this stance, muscles are allowed to relax.  Just slight flexion of the knees, ankles and waist are employed, to maintain fore/aft balance, and keep the body supple as it encounter undulating terrain.  Even when hip angulation is used to promote lateral balance, the torso moves out of structural alignment with the legs, but the bones of the outside leg can still be stacked to provide optimal force resistance strength.  This is called maintaining a Long & Strong outside leg.  Skiers who ski in stances that are consistently over flexed will tax their muscles and tire more quickly.  Stacking is what a skier does when assuming an Athletic Stance.  Ski boots must be set up properly to the feet and body of a skier for optimal stacking to be possible.