Here are two more data sheets from the Birdcage Experiments.
The first data sheet is for the same skier (Steve) shown in THE BIRDCAGE EXPERIMENTS 1. The first two data sheets shown in previous post were for world class skiers who, like Ted Ligety and Mikaela Shiffrin, ski differently than the average recreational skier and even most World Cup racers. Click on the sheet to zoom in.
This Trial involved aggressive GS turns with a free-hinging cuff between front and rear stops set to the skier’s functional specification. Contrary to the common wisdom in skiing, introducing significant resistance to cuff movement in the normal range of ankle flexion forces the soleus muscle to decrease its contractive force in order to overcome the resistance to forward (dorsiflexion) presented by the cuff. Diminished balance, diminished control of the ski and attenuation of the processes that dissipate energy from the interaction with the snow are the result. This was noted as far back as 1987 by Professor M. Pfeiffer of the University of Salzburg (Salzburg, Austria) in his article Kinematics of the Foot in the Ski Boot; “The shaft of the boot should provide the leg with good support, but not great resistance for about two-thirds of the possible arc, i.e., 20 to 22 degrees. Up to that point, the normal, physiologic function of the ankle should not be impeded.” (my emphasis added)
The data sheet below is for an intermediate skier. Part of my hypothesis that was being tested in the Birdcage experiments is that footwear especially ski boots has a training effect on the user. This was demonstrated in the early 1990s at the Human Performance Laboratory at the University of Calgary (Calgary, AB Canada). Based on this premise, it was predicted that a ski boots act as an evolutionary filter for skiing competence in that only skiers with the right foot and leg structure will be able to use their natural intrinsic postural processes. More than any other factor the ski boot determines which skiers will rise to ranks of the elite. Those with incompatible foot and leg structures (ergo – the majority of the skier population) will be forced by the ski boot to develop compensatory mechanisms that will be be much less effective than the processes used by the elite skier. The data sheet below illustrates what happens when an intermediate skier is fit with a ski boot that accommodates the natural intrinsic postural processes. Although it will diminish over time, the ingrained (learned) motor pattern derived from using a conventional ski boot continues to regulate postural activity.
Suddenly we see the pattern of pressure on the front and inner aspects of the boot cuff, high pressure under and behind the heel and minimal pressure under the ball of the foot associated with an unbalanced base of support that necessitates the use of the leg as a compensatory lever to control the edge angle of the ski.