SUBDIVISION OF SKIING TURNS USING GROUND REACTION FORCES

Abstract

Force measurements in alpine skiing using transducers mounted between ski and ski boot have been described by several investigators for selected skiing movements. So far no attempt has been made to subdivide skiing turns into functional phases using the recorded forces as this has been done for running, for example. Thus, the purpose of this study was to subdivide the movement of a skier during turns by means of the forces between the skis and the ski boots. Two gate combinations representing typical standard combinations for slalom and giant slalom were studied. All subjects used the same skis. Each ski was equipped with four one dimensional strain gauge sensors, which were placed between the ski and the ski boot under the outside and the inside of the forefoot and rearfoot. The reaction forces acting perpendicular to the top surface of the ski were measured and transmitted telemetrically. Additionally, the subjects were filmed with a Locam high speed camera in order to determine the trajectories of the skis on the slope. Five racers, listed in the top 10 of the world ranking, were selected for the analysis. The subdivision of the turning motion into phases was determined using the force/time histories of the eight force sensors. Based on the forces measured slalom and giant slalom turns were divided into Four phases. In the load transfer phase the load transfer occurs from the outside ski of the preceding turn to the new outside ski. In the unloading Phase the unloading of the skis takes place. In the load build-UP phase the inside of the outside ski gets loaded and in the loaded phase the inside of the outside ski remains loaded till the load transfer phase of the following turn begins. The beginning and the end of the phases were defined by the recorded force/time histories. In terms of turn initiation and turning of the skis, the movements done in the load transfer phase and the unloading phase cause the initiation and the ones done in the load-build up phase and the loaded phase the turning of the skis. The recorded reaction forces help to characterize the turning technique of elite ski racers. The structuring of the turn movement using reaction forces represents a functional description of a turn. It is suggested that this phase structure of ski turns may be applied to ski training to improve the skiing technique.