INTRODUCTION: In ski jumping the take-off is the most important phase. Good take-off is a complex series of movement and it is performed in extreme and altering conditions. Several significant differences between hill and simulation jumps have been found in several biomechanical analyses (e.g. Virmavirta et all. 2000; Schwameder 2008), and the differences occur mainly due to very different performance conditions. Therefore, the purpose of this study was to examine the effect of friction conditions on the simulated ski jumping take-off. METHOD: National (8) and international (7) level ski jumpers participated in this study. Three simulation jumps in three different friction conditions (µ1-3= 1,00, 0,23, 0,07) were measured from each subject. Take-offs were performed from a force plate, which was placed on a moving sledge. By locking the wheels and changing material between wheels and surface, the friction could be altered. All three force components (x, y, z) under the ball and heel of both feet were recorded. The force data was synchronized with a video (fig. 1), which was used for kinematic analysis. The measuring equipment is part of the ski jumping feedback system of Vuokatti Sports Institute. RESULTS: Several kinetic and kinematic changes were found especially in the lowest friction condition. For example take-off angle increased as the friction decreased (fig.1). In some cases the changes were more pronounced in the national level jumpers. DISCUSSION & CONCLUSION: The measuring system used in this study proved to be appropriate for the given research questions. It was somewhat surprising that the most beneficial results were found on the take-off surface with a lowest friction, which was assumed to be too slippery for proper simulation take-offs. For the proper learning process and motor control it is obvious that the technique in simulation take-offs should be as close as possible to the technique in actual hill conditions. The advantage of the smallest friction condition is that it well reveals the errors in the direction of the force production, which is very difficult to observe even by the experienced coaches in the normal friction conditions. Based on the results of this study it can be recommended that the athletes repeat the simulated take-offs on the surface, which is very close to the actual hill conditions. However, friction conditions are only one element of the differences between the simulated and actual hill jumps and more information is needed to adjust the simulated training closer to the actual hill conditions. --- The hosting University of Jyväskylä is planning to publish conference proceedings "Science and Nordic Skiing III". In case you are interested in this publication please contact the editors (Anni Hakkarainen anni.s.j.hakkarainen@jyu.fi) to become registered for the book.
© Copyright 2015 3rd International Congress on Science and Nordic Skiing - ICSNS 2015. 5-8 June 2015, Vuokatti, Finland. Julkaistu Tekijä University of Jyväskylä; University of Salzburg. Kaikki oikeudet pidätetään. / Kääntänyt https://www.DeepL.com/Translator