A plausible reason why the FreeMotion boot has failed to gain acceptance is that the spring flex concept has not been tested in a medium that allows all the critical variables discussed in my last post to be adjusted to the individual skier. An essential prerequisite to this process is a validated physiological model; one that explains the physiologic processes of skier balance as well as the mechanics and biomechanics associated with the 3-dimensional physical environment of the activity.
While the Birdcage allowed adjustments specific to individual skier requirements to be made and data to be acquired that showed the effects on skier performance, in particular, skier balance, insufficient time and budgetary constraints limited the study of flex curve requirements.
Figures 52 and 55 A through D below show the flex assembly for the Birdcage. The details are disclosed in the section of the patent associated with aforementioned figures.
Figure 56 below shows the different components of the Birdcage shaft adjustment and flex system resistance curve. The details are disclosed in the section of the patent associated with Figure 56.
The photo below shows the actual flex system on the rear of the Birdcage. The nut under the rear stop lug allows for adjustment of the forward lean angle of the shaft. In this photo, the shaft is in the rearmost (hard stop) position with the lug seated against the rear stop nut on the spine.
The photo below shows the gap between the lug and the washer-cyclinder assembly that presses on the coil spring after a pre-set number of degrees of forward flexion.
Experiments were done with several types of coil springs, including compound coil springs where a small coil spring is nested inside a larger spring. The rubber donut at the top of the assembly prevents the ‘brick wall’ deceleration effect that occurs when the coil spring is fully compressed. Different types and assemblies of rubber donuts were tried in conjunction with different coil spring configurations.
In the photo below, the shaft of the Birdcage has rotated forward through the constant low resistance travel segment and is about to compress the coil spring assembly. This position is associated with isometric contraction of the triceps surace (calf muscles) in the SR Stance.
The photo below shows the coil spring in the initial stages of compression.
The effect of flexural qualities of the shaft of a ski boot on skier function and balance require structured studies conducted with instrumentation and data acquisition. Fortunately, papers on such studies have recently been published. I will discuss them in my next post.