Relationship between local ski bending curvature, lean angle and radial force in alpine skiing

The deflection of the ski is a prerequisite for carved turns. The more the ski is edged, the more the ski has to deflect and the more radial force has to be realised in order to keep the whole edge in contact with the snow. To verify this relationship, local ski bending curvature, the lean angle and the radial force were correlated with each other. Characteristic curvature patterns as well as very large correlations (r > 0.7) between the variables were identified.Die Durchbiegung des Skis ist eine Voraussetzung für gecarvte Schwünge. Je stärker der Ski gekantet ist, desto mehr muss der Ski durchbiegen und desto mehr Radialkraft muss realisiert werden, um die gesamte Kante in Kontakt mit dem Schnee zu halten. Um diesen Zusammenhang zu verifizieren, wurden die lokale Skikrümmung, der Neigungswinkel und die Radialkraft miteinander korreliert. Es wurden sowohl charakteristische Krümmungsmuster als auch sehr große Korrelationen (r > 0,7) zwischen den Variablen festgestellt

A Novel Sensor Foil to Measure Ski Deflections: Development and Validation of a Curvature Model

The ski deflection with the associated temporal and segmental curvature variation can be considered as a performance-relevant factor in alpine skiing. Although some work on recording ski deflection is available, the segmental curvature among the ski and temporal aspects have not yet been made an object of observation. Therefore, the goal of this study was to develop a novel ski demonstrator and to conceptualize and validate an empirical curvature model. Twenty-four PyzoFlex® technology-based sensor foils were attached to the upper surface of an alpine ski. A self-developed instrument simultaneously measuring sixteen sensors was used as a data acquisition device. After calibration with a standardized bending test, using an empirical curvature model, the sensors were applied to analyze the segmental curvature characteristic (m−1) of the ski in a quasi-static bending situation at five different load levels between 100 N and 230 N. The derived curvature data were compared with values obtained from a high-precision laser measurement system. For the reliability assessment, successive pairs of trials were evaluated at different load levels by calculating the change in mean (CIM), the coefficient of variation (CV) and the intraclass correlation coefficient (ICC 3.1) with a 95% confidence interval. A high reliability of CIM −1.41–0.50%, max CV 1.45%, and ICC 3.1 > 0.961 was found for the different load levels. Additionally, the criterion validity based on the Pearson correlation coefficient was R2 = 0.993 and the limits of agreement, expressed by the accuracy (systematic bias) and the precision (SD), was between +9.45 × 10−3 m−1 and −6.78 × 10−3 m−1 for all load levels. The new measuring system offers both good accuracy (1.33 × 10−3 m−1) and high precision (4.14 × 10−3 m−1). However, the results are based on quasi-static ski deformations, which means that a transfer into the field is only allowed to a limited extent since the scope of the curvature model has not yet been definitely determined. The high laboratory-related reliability and validity of our novel ski prototype featuring PyzoFlex® technology make it a potential candidate for on-snow application such as smart skiing equipment

Curvature Detection with an Optoelectronic Measurement System Using a Self-Made Calibration Profile

So far, no studies of material deformations (e.g., bending of sports equipment) have been performed to measure the curvature (w″) using an optoelectronic measurement system OMS. To test the accuracy of the w″ measurement with an OMS (Qualisys), a calibration profile which allowed to: (i) differentiates between three w″ (0.13˙ m−1, 0.2 m−1, and 0.4 m−1) and (ii) to explore the influence of the chosen infrared marker distances (50 mm, 110 mm, and 170 mm) was used. The profile was moved three-dimensional at three different mean velocities (vzero = 0 ms−1, vslow = 0.2 ms−1, vfast  = 0.4 ms−1) by an industrial robot. For the accuracy assessment, the average difference between the known w″ of the calibration profile and the detected w″ from the OMS system, the associated standard deviation (SD) and the measuring point with the largest difference compared to the defined w″ (=maximum error) were calculated. It was demonstrated that no valid w″ can be measured at marker distances of 50 mm and only to a limited extent at 110 mm. For the 170 mm marker distance, the average difference (±SD) between defined and detected w″ was less than 1.1 ± 0.1 mm−1 in the static and not greater than −3.8 ± 13.1 mm−1 in the dynamic situations. The maximum error in the static situation was small (4.0 mm−1), while in the dynamic situations there were single interfering peaks causing the maximum error to be larger (−30.2 mm−1 at a known w″ of 0.4 m−1). However, the Qualisys system measures sufficiently accurately to detect curvatures up to 0.13˙ m−1 at a marker distance of 170 mm, but signal fluctuations due to marker overlapping can occur depending on the direction of movement of the robot arm, which have to be taken into account

Relationship between local ski bending curvature, lean angle and radial force in alpine skiing

The deflection of the ski is a prerequisite for carved turns. The more the ski is edged, the more the ski has to deflect and the more radial force has to be realised in order to keep the whole edge in contact with the snow. To verify this relationship, local ski bending curvature, the lean angle and the radial force were correlated with each other. Characteristic curvature patterns as well as very large correlations (r > 0.7) between the variables were identified.Die Durchbiegung des Skis ist eine Voraussetzung für gecarvte Schwünge. Je stärker der Ski gekantet ist, desto mehr muss der Ski durchbiegen und desto mehr Radialkraft muss realisiert werden, um die gesamte Kante in Kontakt mit dem Schnee zu halten. Um diesen Zusammenhang zu verifizieren, wurden die lokale Skikrümmung, der Neigungswinkel und die Radialkraft miteinander korreliert. Es wurden sowohl charakteristische Krümmungsmuster als auch sehr große Korrelationen (r > 0,7) zwischen den Variablen festgestellt

Relationship between local ski bending curvature, lean angle and radial force in alpine skiing

The deflection of the ski is a prerequisite for carved turns. The more the ski is edged, the more the ski has to deflect and the more radial force has to be realised in order to keep the whole edge in contact with the snow. To verify this relationship, local ski bending curvature, the lean angle and the radial force were correlated with each other. Characteristic curvature patterns as well as very large correlations (r > 0.7) between the variables were identified.Die Durchbiegung des Skis ist eine Voraussetzung für gecarvte Schwünge. Je stärker der Ski gekantet ist, desto mehr muss der Ski durchbiegen und desto mehr Radialkraft muss realisiert werden, um die gesamte Kante in Kontakt mit dem Schnee zu halten. Um diesen Zusammenhang zu verifizieren, wurden die lokale Skikrümmung, der Neigungswinkel und die Radialkraft miteinander korreliert. Es wurden sowohl charakteristische Krümmungsmuster als auch sehr große Korrelationen (r > 0,7) zwischen den Variablen festgestellt

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 PyzoFlex® ski prototype was presented for measuring the local ski curvature (w″), demonstrating high reliability and validity. The value of w″ increases as a result of enlargement of the roll angle (RA) and the radial force (RF) and consequently minimizes the radius of the turn, preventing skidding. This study aims to analyze segmental w″ differences along the ski, as well as to investigate the relationship among segmental w″, RA, and RF 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 RA and RF, and six PyzoFlex® sensors were used to measure the w″ progression along the left ski (w1−6″). All data were time normalized over a left-right turn combination. Correlation analysis using Pearson’s correlation coefficient (r) was conducted on the mean values of RA, RF, and segmental w1−6″ 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 (L2 vs. L3) and the three front sensors (L4 vs. L5, L4 vs. L6, L5 vs. L6) was mostly high (r > 0.50) to very high (r > 0.70). During carving turns, the correlation between w″ of the rear (w1−3″) and that of front sensors (w4−6″) of the outer ski was low (ranging between −0.21 and 0.22) with the exception of high correlations during COM DC II (r = 0.51–0.54). In contrast, for parallel ski steering, the r between the w″ of the front and rear sensors was mostly high to very high, especially for COM DC I and II (r = 0.48–0.85). Further, a high to very high correlation (r ranging between 0.55 and 0.83) among RF, RA, and w″ of the two sensors located behind the binding (w2″,w3″) in COM DC I and II for the outer ski during carving was found. However, the values of r were low to moderate (r = 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 w″ 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