Ski jumping flight : a kinematic analysis of the mid-flight and preparation for landing phases

Abstract

Competitive success in the sport of ski jumping is made possible through the optimal performance of junkers during flight. While the flight phase has been the subject of several scientific investigations, there remain many questions concerning the optimization of this most important phase. The purpose of this study was to identify and quantify specific kinematic variables of both the mid-flight and the preparation for landing phases of ski jumping flight. Secondly, the study sought to examine the statistical contribution of variables in both phases to the distance jumped. Finally, an attempt was made to develop a model which would provide a general view of the structure of the relationships among analyzed variables. The subjects for this investigation were 50 highly skilled nordic combined competitors participating in the 1996 World Cup K-88 event. Fourty trials from the first round of competition were selected for inclusion in the data analysis. The data for the 40 analyzed subjects was collected using two cameras mounted on Peak Performance Pan and Tilt Heads. The jumpers were taped as they passed through the field of view, from 55 to 85 meters on the jump hill. The Pan and IHt hardware enabled the data to be collected over a wide field of view which resulted in the analysis of both the mid-flight and preparation for landing phases. Values for the distance jumped and the inrun velocity were collected from the official results printed by the FIS competition committee. The Peak Performance 3D Video Analysis System was used to extract the horizontal and vertical coordinates for a 19 point segmental model The center of truss was calculated for the model, which included the masses of skis, helmets and boots. Data was smoothed and processed to compute linear displacements and velocities and angular displacements in the three planes of motion. Statistical treatment of the raw kinematic data was performed using the appropriate computer programs from SPSS. Correlation analyses were conducted on the variables of the mid-flight and preparation for landing phases to determine the strength of any relationships between the selected variables and distance jumped. Both frill and stepwise regression analyses were conducted on the two analyzed phases of fright to assess the predictability of the dependent variable, distance jumped. Also, a varimax rotated factor analysis was developed for each of the mid-flight and preparation for landing phases to examine the complex intercorrelations between independent variables. The results of the study revealed the kinematic variables that are associated with increasing the distance jumped. A general model of the relationships between independent variables and their contribution to the distance jumped gave insight into the traits that may be optimized in order to improve ski jump performance. The results of the mid-flight phase suggested that, in order to increase distance jumped, athletes should attain a compact, forward flight position with a small angle of attack, optimize previous movements in order to achieve a high flight curve, and maximize the inrun velocity. The preparation for landing results indicate that the best jumpers had an open flight position and a greater negative vertical velocity. Flight positions in both analyzed phases were observed to have a large effect on aerodynamic factors and the distance jumped.