A LONGITUDINAL STUDY OF INTRA-INDIVIDUAL VARIABILITY IN THE EXECUTION OF THE IN-RUN POSITION IN SKI JUMPING
Keywords: videography, ski jumping, in-run, intra-individual variability
AbstractINTRODUCTION: The change of flight in ski jumping (V-style) has influenced a change in the take-off process. When considering this fact, it is necessary to determine whether the same applies to the in-run position – one of the basic phases of ski jumping. The ski jumper must master three basic tasks of the in-run position: maintenance of equilibrium, acquisition of maximum approach velocity and preparation for take-off. The main goal of this paper was to determine whether a set of various models of the in-run position exists for selected competitors. METHODS: Data for this study were collected from the Intersport tournee Innsbruck between 1992 and 1998 at a distance of 18 m prior to the edge of the jumping hill. A 2D kinematic analysis was used to evaluate the in-run position of the ski jumpers (500 analyses). The in-run position was evaluated using eight angle parameters. Jumpers were chosen from among the competitors who jumped at least four times in this event. Assessments of inter-individual and intraindividual variability were made. For analysis of the results, a computer statistical package ‘Statgraphics’ (one-way analysis of variance, Kruskal-Wallis one-way analysis by ranks, cluster analysis) was used. RESULTS: A large range for the analyzed angles existed for the group of selected competitors. The changes occurring among the selected segments of the body varied with each individual sportsman. The athletes under study could be divided into several qualitative groups: high stability of the lower extremities position (subjects 1 and 2), high stability of the upper extremities position (subject 3), high stability of the lower extremities with regard to the trunk position (subjects 4 and 5), in-run position with low stability (subject 6), etc. The position of the center of gravity for subjects 1, 4, 7, 8 and 9 was often stable even with high variability of the other parameters. The data supported the concept that the influence of anthropometric and physiological characteristics is very important. CONCLUSIONS: Changes in the in-run position were found in all ski jumpers in the period between 1992 and 1998. Statistically significant differences (interindividual variability) existed among years of measurement. Within the group of selected ski jumpers the execution of the in-run position varied for both body position and the position of the segments of the body. There existed an individual solution of this movement situation for most ski jumpers – it can be called an individualized model of the in-run position.
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