INTRODUCTION: Ski boots are an important piece of equipment for alpine skiing: they play a vital role both in protecting the skier from injuries and transmitting loads to the ski. Ski boots exhibit complex nonlinear material deformation under load [1]. Measuring those deformations in-run could provide valuable information for manufacturers (e.g. optimizing mass) and for users (e.g. choosing an appropriately stiff boot). Various methods have already been tested: angular potentiometers [2], electrogoniometers [2] and strain gauges [3]. A new method is proposed which uses distributed IMUs. This could provide a less intrusive, more accurate, complete 3D deformation of ski boot at multiple locations even through the presence of mechanical joints, large shell deformations and liner compression. METHODS: A Scarpa Quattro SL boot was equipped with four IMUs (A, B, C, D) positioned as shown in the figure. The 3D angular velocity was recorded at 1000Hz and stored on a datalogger strapped to the user`s tibia. A custom post-processing algorithm obtains 3D orientation for each point and calculates the difference in orientation for each point with regards to IMU A, chosen as a boot-fixed reference point. This difference corresponds to the angular deformation for each point and is de-drifted using a new method as to correct for IMU noise and other errors. A simple preliminary test was performed indoors. The subject alternated between simulated movements (swinging the boot once from side to side) and loading the boot with his full weight. RESULTS/DISCUSSION: Flexion (deformation around Y axis) is plotted for 3 measurement points (B, C, D), with reference to A. Deformation around X (torsion) and Z axis are also available, but not shown here. During the off ground simulated carving movement, flexion remained close to zero, as expected. Stability of the deformation during this moment shows that the signal was successfully de-drifted. During loading, flexion of the front of the cuff (DA) was the greatest (7deg), flexion at the back of the cuff (B-A) was small and flexion of the base of the boot (C-A) was in the negative direction. These measurements align with expected boot behavior, supporting the validity of our system for capturing realistic deformations. CONCLUSION: A novel IMU-based ski boot deformation system was developed. This system incorporates inertial navigation and a custom de-drifting technique to calculate 3D angular deformation of multiple points of the boot. Preliminary results suggest the system`s potential for accurate deformation measurements, and further testing in real skiing conditions will validate its practical application.
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