A GENERAL VERSUS AN INDIVIDUAL MODEL OF THE SKI JUMPING TECHNIQUE

  • F. Vaverka
  • M. Janura
  • M. Elfmark
  • M. McPherson

Abstract

INTRODUCTION The stochastic models which are based on the results of biomechanical analyses of the ski jump (kinematic analysis, eg ARNOT, 1995; dynamic analysis of the take-off, e.g. VAVERKA, 1987) help us to solve the basic question of the relationship between the biomechanical variables and the criterion (validity). Statistical models form the output used to select the set of observed variables which represent the parameters for the effective ski jumping technique The results of many studies have shown that the validity of the biomechanical variables are very different in different phases of the ski jump. Contrary to what has been seen in practice it has been repeatedly found that the statistical dependence between take-off variables and the criterion are relatively low (R2 = 0.2-0.3) In comparison with the flight phases (R2= 0.6-0.9). The hypothesis of an individual model for the take-off is supported by the multifactor theory of the take-off (VAVERKA, 1987) in which the principle optimisation of the take-off factors and individualisation of the take-off have been defined. This paper represents an attempt to determine a practical model for ski-jumping technique. METHODOLOGY The system for the 20 kinematic analyses of the ski-jump (VAVERKA, 1994; take-off phase) and the Peak Performance Analyses System (flight phase) have been used in this study. The set of 11 variables for both the take-off and flight phase served as the input matrix for the statistical analyses (Intersporttournee event in Innsbruck 1993-1995, n=155). The set of 18 world class level athletes were selected for the study of intra-individual variability for the take-off phase. The average number of analysed take-offs by individuals was 7.6 jumps (range=5-13 takeoffs). Analyses of variance, multiple range of analyses of variance, regression, correlation and factor analyses computed by the STATGRAPHICS package were used. RESULTS The results of the statistical analyses on the inter-individual variability (5 matrices for the take-off phase and 6 matrices for the flight phase) demonstrated a low level of validity for the take-off parameters (R2 =0.15-0.20) and increased validity for the flight parameters (R2=0. 7-0.8) The statistical analyses of differences between individuals has shown that there are the significant differences in the aerodynamics and forward-backward position for the centre of gravity (relates to the factor of rotation). CONCLUSIONS The results of the statistical analyses have shown the predominant tendencies of individualisation of the take-off model. A very successful take-off for an individual could be realised by the use of many different patterns of movement. From the results of the flight phase we can accept a general pattern for the performance this ski-jumping phase REFERENCES Arndt, A. et al. (1995). Journal of Applied Biomechanics, 11, 224-237. Vaverka, F. (1987). Biomechanics of Ski-jumping (Czech language), Monograph, Univerzita Palackeho Olomouc, 235 pp. Vaverka, F. et al. (1994). In. Biomechanics in Sports XII, Proceedings, 285-287.