Flexural Behavior of Ski Boots Under Realistic Loads – The Concept of an Improved Test Method

The design of ski and ski touring boots should consider three key elements: performance, safety and comfort. For all three aspects, the boot's (shaft) flexural behavior is one of the crucial characteristics. Knowing the importance of this design parameter it is surprising that up to now no generally accepted standardized method exists to test and quantify the stiffness of the boot. First test methods, developed in the late eighties, used a leg prosthesis loaded with a horizontal force at the top of the shank in order to apply a bending moment to the boot hinge. Since then the basic principle has not been changed and it is widely used to quantify the dorsal and plantar flexion under slope conditions as well as the effect of buckle closure, temperature and fit of the boot. This common approach however neglects some of the important boundary conditions such as the realistic plantar pressure distribution underneath the artificial foot or the correct location and shift of the point of force application during the flexion movement. The aim of this study was to design a new test bench which overcomes some of the previous limitations thus being able to improve validity of the load simulation. The major addition to the current state is that the new test bench simulates ground reaction forces by using a pneumatic driven active leg-prosthesis generating an internal extension moment in knee and ankle. Further a linear bearing allows simultaneous displacement of the foot in the sagittal plane, simulating forward or backward shift of the center of pressure, which is typical for skiing maneuvers. The presentation will illustrate the theory behind this new concept and describe the details of its design.