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

Abstract

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 PyzoFlex® ski prototype was presented for measuring the local ski curvature ((Formula presented.)), demonstrating high reliability and validity. The value of (Formula presented.) increases as a result of enlargement of the roll angle ((Formula presented.)) and the radial force ((Formula presented.)) and consequently minimizes the radius of the turn, preventing skidding. This study aims to analyze segmental (Formula presented.) differences along the ski, as well as to investigate the relationship among segmental (Formula presented.), (Formula presented.), and (Formula presented.) 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 (Formula presented.) and (Formula presented.), and six PyzoFlex® sensors were used to measure the (Formula presented.) progression along the left ski ((Formula presented.)). All data were time normalized over a left-right turn combination. Correlation analysis using Pearson’s correlation coefficient ((Formula presented.)) was conducted on the mean values of (Formula presented.), (Formula presented.), and segmental (Formula presented.) 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 ((Formula presented.) vs. (Formula presented.)) and the three front sensors ((Formula presented.) vs. (Formula presented.), (Formula presented.) vs. (Formula presented.), (Formula presented.) vs. (Formula presented.)) was mostly high ((Formula presented.) > 0.50) to very high ((Formula presented.) > 0.70). During carving turns, the correlation between (Formula presented.) of the rear ((Formula presented.)) and that of front sensors ((Formula presented.)) of the outer ski was low (ranging between −0.21 and 0.22) with the exception of high correlations during COM DC II ((Formula presented.) = 0.51–0.54). In contrast, for parallel ski steering, the (Formula presented.) between the (Formula presented.) of the front and rear sensors was mostly high to very high, especially for COM DC I and II ((Formula presented.) = 0.48–0.85). Further, a high to very high correlation ((Formula presented.) ranging between 0.55 and 0.83) among (Formula presented.), (Formula presented.), and (Formula presented.) of the two sensors located behind the binding ((Formula presented.)) in COM DC I and II for the outer ski during carving was found. However, the values of (Formula presented.) were low to moderate ((Formula presented.) = 0.04–0.47) during parallel ski steering. It can be concluded that homogeneous ski deflection along the ski is an oversimplified picture, as the (Formula presented.) 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.