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Sensors

| 2023

Technique-Dependent Relationship between Local Ski Bending Curvature, Roll Angle and Radial Force in Alpine Skiing

Skiing technique, and performance are impacted by the interplay between ski and snow. The resulting deformation characteristics of the ski, both temporally and segmentally, are indicative of the unique multi-faceted nature of this process. Recently, a PyzoFlexยฎ ski prototype was presented for measuring the local ski curvature (๐‘คโ€ณ), demonstrating high reliability and validity. The value of ๐‘คโ€ณ increases as a result of enlargement of the roll angle (๐‘…๐ด) and the radial force (๐‘…๐น) and consequently minimizes the radius of the turn, preventing skidding. This study aims to analyze segmental ๐‘คโ€ณ differences along the ski, as well as to investigate the relationship among segmental ๐‘คโ€ณ, ๐‘…๐ด, and ๐‘…๐น for both the inner and outer skis and for different skiing techniques (carving and parallel ski steering). A skier performed 24 carving and 24 parallel ski steering turns, during which a sensor insole was placed in the boot to determine ๐‘…๐ด and ๐‘…๐น, and six PyzoFlexยฎ sensors were used to measure the ๐‘คโ€ณ progression along the left ski (๐‘คโ€ณ_1-6). All data were time normalized over a left-right turn combination. Correlation analysis using Pearsonโ€™s correlation coefficient (๐‘Ÿ) was conducted on the mean values of ๐‘…๐ด, ๐‘…๐น, and segmental ๐‘คโ€ณ_1โˆ’6โ€ณ for different turn phases [initiation, center of mass direction change I (COM DC I), center of mass direction change II (COM DC II), completion]. The results of the study indicate that, regardless of the skiing technique, the correlation between the two rear sensors (๐ฟ2 vs. ๐ฟ3) and the three front sensors (๐ฟ4 vs. ๐ฟ5, ๐ฟ4 vs. ๐ฟ6, ๐ฟ5 vs. ๐ฟ6) was mostly high (๐‘Ÿ > 0.50) to very high (๐‘Ÿ > 0.70). During carving turns, the correlation between ๐‘คโ€ณ of the rear (๐‘คโ€ณ_1โˆ’3โ€ณ) and that of front sensors (๐‘คโ€ณ_4โˆ’6โ€ณ) of the outer ski was low (ranging between โˆ’0.21 and 0.22) with the exception of high correlations during COM DC II (๐‘Ÿ = 0.51โ€“0.54). In contrast, for parallel ski steering, the ๐‘Ÿ between the ๐‘คโ€ณ of the front and rear sensors was mostly high to very high, especially for COM DC I and II (๐‘Ÿ = 0.48โ€“0.85). Further, a high to very high correlation (๐‘Ÿ ranging between 0.55 and 0.83) among ๐‘…๐น, ๐‘…๐ด, and ๐‘คโ€ณ of the two sensors located behind the binding (๐‘คโ€ณ_2,๐‘คโ€ณ_3) in COM DC I and II for the outer ski during carving was found. However, the values of ๐‘Ÿ were low to moderate (๐‘Ÿ = 0.04โ€“0.47) during parallel ski steering. It can be concluded that homogeneous ski deflection along the ski is an oversimplified picture, as the ๐‘คโ€ณ pattern differs not only temporally but also segmentally, depending on the employed technique and turn phase. In carving, the rear segment of the outer ski is considered to have a pivotal role for creating a clean and precise turn on the edge.

Keywords

bending sensors, flexion, PyzoFlex, ski bending, ski deflection

Author/s

Christoph Thorwartl, Andreas Tschepp, Michael Lasshofer, Helmut Holzer, Martin Zirkl, Matthias Hammer, Barbara Stadlober, Thomas Stรถggl

Institution / Department

Department of Sport and Exercise Science, University of Salzburg, Hallein

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