There is a predominant camp in skiing who claim that the ski boot is a handle that skiers use to put their skis on edge. This is the central theme of the pure carved turn camp that posits that expert skiing is simply a matter of holding both skis on edge at the same angle and letting the sidecut of the ski make take control and ‘do their thing’.
Try this. Stand in sock feet or even in shoes on a floor or other firm, level surface. Drive one of your knees towards the L-R center of your body as if you were driving the knee into a turn (i.e. – angulating the knee). What happens? Nothing. The foot stays flat on the floor and the joints of the ankle accommodate the knee angulation (ad-adbuction/internal-external rotation). Put a ski boot on one foot. Now balance on that foot and try to “drive your knee into the turn” (towards the center of the body). What happens? Not much. Why? Because the weight of your body (COP) is under your heel where it is pressing down on the center of the boot where it is preventing it from rotating onto the inner edge of the sole. When the shaft of a ski boot is used in this manner, COP will always be under the heel. High pressure first metatarsal COP and heel-first metatarsal pressure differential management are not possible.
In order for a ski boot to act as handle with which to rotate a ski onto its edge inside, the weight of the body must to be raised off the surface the skier is standing. When a ski instructor demonstrates how driving the knee of one leg into the turn puts a ski on edge on flat terrain (A-frame), most of their weight is on the other foot and leg. If the instructor demonstrates knee angulation while standing on both skis in traverse, the shafts of both boots are already pre-loaded on the legs which are acting as a source of GRF for the GRF that is missing under the portion of the skis outboard of the edges. These demonstrations are nothing more than amateur parlour tricks, illusions from a carnival sideshow magicians act. They bear no resemblance to what the worlds best skiers are doing, and have been doing for close to a hundred years. In all these parlour tricks, COP is under the heel. In this position COP is distributed along the center axis of a ski towards the shovel and tail. No force is acting across the inside edge. The problem is not with those who make such illogical demonstrations but with those who fail to see through the obvious illusion and accept the premise without question, even though the manner in which the instructor skis usually bears no resemblance to what he or she teaches.
In my next post I will describe the mechanical and biomechanical differences of heel only COP and heel/first metatarsal COPs and the effect on the ski of the resulting pressure differential management. This is the central issue in skiing, the meat in the sandwich.