KINEMATIC CHARACTERISTICS OF SKI-JUMPING ON JUMPING HILLS WITH DIFFERENT CRITICAL POINTS

Abstract

The "take-off' of ski-jumpers is a very complex motor action. The jumper must, at great velocity (90 - l I0 km/h) and in a very short time (0.3 to 0.4 s), resolve five relatively simple motor problems: vertical velocity, aerodynamical aspect, precision, rotation and arm-action (Vaverka, 1987). Findings of researches and praxis show a significant intra-individual variability of the execution of the "take-off' technique. The successfulness of the "take-off' is influenced, beside a multitude of factors of the jumper's psychosomatic status, also by some external, objective factors, like the construction of the jumping hill, the approach velocity, climatic and meteorological conditions, quality of the sports equipment, etc. In regard to the "take-off' on hills with different critical points, we hypothetically suppose that different velocities and constructional parameters of the hill can influence the kinematic characteristics of the "take-off'. The purpose of this study was to find the stability of the kinematic structure of the "take-off' on jumping hills with different critical points and constructional characteristics. The study was carried out at three competitions for the World Cup, those at which most of the top world jumpers participated: - World Cup Planica, December 1993, K=90 m - World Cup Intersport Tour Innsbruck, January 1994, K=l 12 m - World Championship in ski flight Planica, March 1994, K=185 m A special programme package was used for the kinematic analysis, based on a two dimensional analysis of the defined parametres, among which the majority are parametres showing the different angles and velocity changes. At each competition, the best jumpers were chosen (n=12 - 15). The gathered data was, in accord with the stated aims of the research, treated by the proper statistical methods.