?Stacked?, conveys a static position, (like piling bricks on top of each other) and doesn?t convey how to approach any benefits it ?should? communicate. Joints and bones should remain properly aligned, even when moving from one turning alignment to the next. I don?t ever think of myself as stacked. I?m never in a position long enough, and stacking refers to bones on top of each other, rather than the constant activity of tendons, ligaments and muscles making adjustments to maintain a balanced state. Now that would be Co-contraction.
Notice in PMTS, we use words and definitions that describe movement: Counterbalancing, Counteracting, and Tipping.
Co contraction is not a PMTS invention, it is however a description of skiing initiated by movements at the bottom of the kinetic chain and that originate in PMTS literature; therefore it can?t possibly be right, right?
Co contraction doesn?t connote static positions, it means: constant movement of antagonistic, yet cooperative muscle groups, to stabilize joints, and keep mass above the moving joint, in balance. I know, that's not complicated enough for ski instructors to understand!
It is very hard to describe movement in the fore/aft balance relationship, (compared to lateral balance) because fore/aft balance requires management of numerous joints with many muscle groups, originating at different joints. Once your mass moves too far from the balance point over a joint, co-contraction of that joint halts. The muscles have to readjust to an out of balance situation and relocate the mass above the joint to regain in alignment, where co-contraction can manage balance. Stacking doesn?t address these situations.