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Biomechanical Analysis of Alpine Skiers Performing Giant Slalom Turns

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Biomechanical Analysis of Alpine Skiers Performing Giant Slalom Turns Unicentre CH-1015 Lausanne http://serval.unil.ch Year : 2012 Biomechanical analysis of alpine skiers performing giant slalom turns Meyer Frédéric Meyer Frédéric , 2012, Biomechanical analysis of alpine skiers performing giant slalom turns Originally published at : Thesis, University of Lausanne Posted at the University of Lausanne Open Archive. http://serval.unil.ch Droits d’auteur L'Université de Lausanne attire expressément l'attention des utilisateurs sur le fait que tous les documents publiés dans l'Archive SERVAL sont protégés par le droit d'auteur, conformément à la loi fédérale sur le droit d'auteur et les droits voisins (LDA). A ce titre, il est indispensable d'obtenir le consentement préalable de l'auteur et/ou de l’éditeur avant toute utilisation d'une oeuvre ou d'une partie d'une oeuvre ne relevant pas d'une utilisation à des fins personnelles au sens de la LDA (art. 19, al. 1 lettre a). A défaut, tout contrevenant s'expose aux sanctions prévues par cette loi. Nous déclinons toute responsabilité en la matière. Copyright The University of Lausanne expressly draws the attention of users to the fact that all documents published in the SERVAL Archive are protected by copyright in accordance with federal law on copyright and similar rights (LDA). Accordingly it is indispensable to obtain prior consent from the author and/or publisher before any use of a work or part of a work for purposes other than personal use within the meaning of LDA (art. 19, para. 1 letter a). Failure to do so will expose offenders to the sanctions laid down by this law. We accept no liability in this respect. FACULTÉ DES SCIENCES SOCIALES ET POLITIQUES INSTITUT DES SCIENCES DU SPORT Biomechanical analysis of alpine skiers performing giant slalom turns THÈSE DE DOCTORAT présentée à la Faculté des sciences sociales et politiques de l’Université de Lausanne pour l’obtention du grade de Docteur ès sciences du sport par Frédéric Meyer Directeur de thèse Dr. Fabio Borrani LAUSANNE 2012 2 Résumé Le sport de compétition bénéficie depuis quelques années des progrès technologiques apportés par la science. Les techniques d’entraînement, le suivi des athlètes et les méthodes d’analyse deviennent plus pointus, induisant une nette amélioration des performances. Le ski alpin ne dérogeant pas à cette règle, l’objectif de ce travail était d’analyser la technique de skieurs de haut niveau en slalom géant afin de déterminer la quantité d’énergie fournie par les skieurs pour augmenter leur vitesse. Pour ce faire, il a été nécessaire de developer différents outils d’analyse adaptés aux contraintes inhérentes aux tests sur les pistes de skis; un système multi caméras, un système de synchronisation, un modèle aérodynamique et des plateformes de force ont notamment été développés. Les analyses effectuées grâce à ces différents outils ont montré qu’il était possible pour certains skieur d’augmenter leur énergie d’environ 1.5 % grâce au travail musculaire. Cependant, les athlètes n’ont en moyenne pas réussi à utiliser leur travail musculaire de manière efficace. Ce projet a également rendu possible des analyses adaptées aux conditions d’entraînement des skieurs en proposant des outils fonctionnels tels que l’analyse du drift grâce à des capteurs inertiels et GPS, ainsi que l’analyse simplifiée de trajectoires grâce au suivi de points morphologiques. L’auteur espère que ce travail servira de base pour approfondir les connaissances de la technique en ski alpin. 3 Abstract Over the past few years, technological breakthroughs have helped competitive sports to attain new levels. Training techniques, athletes’ management and methods to analyse specific technique and performance have sharpened, leading to performance improvement. Alpine skiing is not different. The objective of the present work was to study the technique of highy skilled alpine skiers performing giant slalom, in order to determine the quantity of energy that can be produced by skiers to increase their speed. To reach this goal, several tools have been developed to allow field testing on ski slopes; a multi cameras system, a wireless synchronization system, an aerodynamic drag model and force plateforms have especially been designed and built. The analyses performed using the different tools highlighted the possibility for several athletes to increase their energy by approximately 1.5 % using muscular work. Nevertheless, the athletes were in average not able to use their muscular work in an efficient way. By offering functional tools such as drift analysis using combined data from GPS and inertial sensors, or trajectory analysis based on tracking morphological points, this research makes possible the analysis of alpine skiers technique and performance in real training conditions. The author wishes for this work to be used as a basis for continued knowledge and understanding of alpine skiing technique. 4 Acknowledgements I would like to thank the following people: - Marie, my sweet half, my significant other, perhaps the person who contributes the most in this dissertation, spending hours in reading and correcting my articles, supporting me during all these years of labour and pushing me when necessary. I wouldn’t have achieved this project without you and I’m looking forward to take on new challenges together! - My parents Jean-Claude and Martine who supported me in all the challenges I went through, always pushing me to give my best in my studies and in my practice of sports. You teached me how to ski and accompanied me during all these years of competition. You gave me the curiosity and the taste of surpassing myself, necessary to achieve this project. - Dr Fabio Borrani, my supervisor, for the trust he placed on me since the beginning, for giving me the opportunity to work on this wonderful subject, for the long hours spent on Skype to work on the encountered issues and for welcoming me in Auckland during my stay. - My sister Sandrine, who contributed to this project with her master’s final project and did an awesome work at digitalizing my images through long and boring hours of clicking. - Dr Adrian Waegli and his colleagues from the TOPO lab at the EPFL, for the guidance on all the GPS aspects and the work done together. - Dr Thomas Lochmatter and Dr Alexander Bahr for the development of the wireless synchronization system in a very shot period of time and the uncounted hours of welding. - Dr Alain Shorderet, Dr Alain Prenleloup and the students of the LCSM lab of the EPFL, who developed a dedicated force platform, and more specifically Alain Prenleloup for his investment to have the material ready for the field tests and his active participation to the field tests. 5 - My colleagues Xavier and Yves, who were my first victims when I had to test a new sexy suit. We spend great time in our office in the early days of the institute! - My cameramen and colleagues Giacomo, Stefano, Antoine, Gregory, Etienne, for the long hours spent on the snow in Stoos, escorting me the first day of test when there was just too much fresh snow for doing anything but riding, and filming the athletes with professionalism the next days. I’m looking forward to hear the Rolling Stoos again! - Dr Nicolas Kurpiers and Dr Paul Mc Alpine for their precious help in the ski hall and for welcoming me in the Sport and Exercice Science Institute at Auckland University. - Dr Michel-Alexandre Cardin, Dr Nicolas Kurpiers, Dr Arne Voegle and Dr Federico Formenti for their precious support in writing this document. - David le Pelley for granting me access to the windtunnel and for his guidance on the technical aspects of this experiment. - Martin Langenegger from Stoos, who prepared our visit to his ski resort and provided the logistic. - Peter Lauppi for his support at Swiss Ski, his interest in this project and his help to organize the field tests during the Swiss championship in Stoos. - Prof. Alberto Minetti, Dr. Nicolas Coulmy, Dr. Robert Reid, Prof. Fabien Ohl and Prof. Gregoire Millet who accepted to be members of the jury and bring their expert views to the project - Finally, a special thanks to all the athletes who volunteered their time for participating in this project, wearing strange equipments. Without your contributions, nothing would have been possible. 6 Table of content Imprimatur ………………………………………………………………………….. 2 Résumé ………………………………………………………………………………..……. 3 Abstract ……………………………………………………………………….……………. 4 Acknowledgements……………………………………………………....……………. 5 Table of content …………………………………………………………………... 7 List of Figures …………………………………………………………...…………...…11 List of Tables …………………………………………………………………..……….. 15 Abreviations and Symbols ……………………………………………..…………. 17 1. Introduction ........................................................................................ 21 1.1. Background.................................................................................. 21 1.2. Research plan.............................................................................. 22 1.3. Structure of the dissertation ......................................................... 23 2. Methodological advances in snow sports biomechanics............... 25 2.1. Kinematics ................................................................................... 25 2.1.1. Two-dimensional video analysis ................................................... 26 2.1.2. Three-dimensional video analysis................................................. 27 2.1.3. Technical considerations about video based measurements ........ 29 2.1.4. Goniometers................................................................................
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