INTRODUCTION: In ski jumping, the v-style as a more effective ski Position superseded the parallel style, because of greater drag und lift forces that is caused when opening the skis (Mroß & Mahnke, 1994; Ito, Seo & Asai, 2008). When opening the ski for the v-style human anatomy produces a tilting of the skis. A greater tilting of the skis reduces the drag und lift forces which can act on them. This interrelation has to be taken into account when trying to optimize the v-style in ski jumping. Previous findings were based on wind channel studies (Kreibich, Mahnke & Müller, 2004) including the v-opening angle, the ski angle of attack and the tilting angle. Under the conditions of a real ski jump only the v-opening angle and the ski angle of attack could be determined by 3D-videophotogrammetry. The application of inertial measurement units (IMU) might overcome that problem. Thus, the aim of this study is to measure the ski orientation angles including the tilting angle in a real ski jumping environment based on IMUs. METHOD: For our studies we applied inertial measurement units (MTx, Xsens Technologies). This IMU measured 3D acceleration, 3D rate of turn as well as 3D earth-magnetic field data at a sample rate of 100 Hz and calculated the orientation of each ski. Initially, under laboratory conditions and applying a jumper's model, the IMU was evaluated with respect to v-opening angle, ski angle of attack and tilting angle and compared with the results of 3D-videophotogrammetry. In August 2010 the IMU was applied in a practical study under field conditions for the first time. An athlete of the German national team performed six measurement runs on the Fichtelberg ski jumping hill (Oberwiesenthal, Germany) equipped with two inertial measurement units and a data logger. The sensor units were attached to the left and the right ski behind the bindings. RESULTS and DISCUSSION: The results of our measurements of the ski tilting angle under laboratory conditions show that the IMUs produce a mean deviation of 1° compared to 3D-videophotogrammetry, which is sufficiently exact. In our studies of the real flight in ski jumping we were able to measure the parameters of the v-position of the skis including the tilting angle. The weight and the mechanical characteristics of the IMU did not affect the athlete adversely. As a consequence of a non-synchronous v-position of the skis and of intra-individual differences when executing the jumping movements we found differences for the tilting angle between the individual jumps as well as between the left and the right ski. CONCLUSION: With these studies it was possible to monitor all essential parameters of the v-position of the skis. Thus in future studies a differentiated evaluation of the efficiency of the v-style will become possible.
© Copyright 2012 Science and Skiing V. 5th International Congress on Science and Skiing, Dec. 14 - 19, 2010, St. Christoph am Arlberg. Published by Meyer & Meyer Sport (UK) Ltd.. All rights reserved.