Introduction: Before this project, a ski jumping hill equipped with a kinematic and dynamic measuring system did not exist in Austria. Thus the aim of this work was to develop such a measurement system allowing precise technical analysis at the BergIsel jumping hill. Comparisons of the velocity of the centre of gravity, calculated by the kinematic and dynamic measuring data, were used to validate the measuring and analysis system. Methods: The three force components were sampled (1000 Hz) by seven force platforms (KISTLER, Typ Z18401-100), which were fixed about 10.5 m on the jumping table. The force data were smoothed with cubic splines. For a kinematic registration of a field of view of 7 m before to 2 m behind the jumping table two highspeed cameras with a sampling frequency of 230 Hz and a resolution of 1025 x 512 pixel (Vosskühler, Typ HCC-1000 CMOS) were used. A special software program using Labview 7.1 (National Instruments) was developed in order to digitize the image coordinates of the joint points. The software permits automatic tracking with manual correction. From the image coordinates the 2-d coordinates of the joint points were determined by the DLT-method. The 2-d coordinates were smoothed with quintic splines. A photoelectric beam was used for triggering the kinematic and dynamic measuring systems. Two wind gauges were installed next to the jumping table. Five elite Austrian ski jumpers were recorded during three training jumps under windless conditions (speed of wind less than 0.5 m/s). Every jump was digitized three times by two different persons. The velocity of the centre of gravity was determined in two different ways. In the first method, a six segment model of the ski jumper`s body was used to compute the centre of gravity and its velocity was determined from the first derivative of the smoothed coordinates. In the second method the measured force normal to the jumping table was integrated numerically. The dynamic calculation did not consider the aero dynamical lift. Results and Discussion: The maximum difference between the repeated digitized data of the joint angles was three degrees. The maximum velocity difference of the centre of gravity between the multiple digitalisations was 0.15 m/s. The difference of velocity of the centre of gravity, calculated kinematically and dynamically, was on average 5 % with a maximum of 30 %. The results show that this system is useful for a precise measurement of the angles during ski jumping. However, the occasional large differences between the two methods` calculated velocities of the centre of gravity must be further examined. The influence of the lift will be determined through wind tunnel readings in future projects.
© Copyright 2005 International Congress Mountain & Sport. Updating study and research from laboratory to field. 11th-12th November 2005. Rovereto (TN) - Italy. Programme and book of abstracts. Veröffentlicht von Centro Interuniversitario di Ricerca in Bioingegneria e Scienze Motorie. Alle Rechte vorbehalten.