INTRODUCTION: Cross-country (x-c) skiing and skijumping are sport events which have been studied quite frequently with kinematic methods. Their merit must be appreciated, because this type of research has considerably advanced understanding of the physical requirements of these two winter sports. Kinetic approaches are more difficult to apply, although needed to understand more clearly the mechanisms involved, The present report gives an overview of the recent developments of the force platform Systems constructed in Vuokatti Sport Institute in Finland for research of x-c skiing and skijumping. METHOD: The methodological development was based on earlier experience of force-plate constructions (e.g. Komi, 1987; Virmavirta and Komi, 1989). For x-c skiing the problem in force measurements is the requirement for recording ski and pole forces separately with four rows of platforms. The speed of skiing in diagonal technique is also quite fast and the individual strides (skis) and arm actions (poles) are rather long. The system needs to capture several consecutive steps. For skijumping, the length requirement applies to extend the force platform to cover the entire take off including most of the inrun curve of the jumping hill. Consequently for a 90 m jumping hill, the force platform must cover the last 15 m of the take off area. The constructions were planned so that the individual force plates of 1 m long are the same for both events. Thus the following discussion focuses in more detail on x-c skiing. The 20 m long system consisting of four rows of 1 m long individual plates was connected electrically in series, row by row. The two middle rows (for skis) are covered with snow simifarty to the actual ski track. The metal surfaces of the outer two rows for the poles are covered with the glued tartan type material, the surface of which is on the same level as the two middle rows. The strain gauges in individual plates record the forces in two directions (Fz, Fy) and the resonant frequencies in both directions are 150 Hz. The entire 20 m long system was then installed in the Ski Tunnel of the Vuokatti Sport Institute, where different slope conditions of diagonal x-c skiing can be measured all year round with controlled snow, temperature and humidity conditions. In skijumping the two rows of similar construction as in x-c skiing are mounted permanently for two different size jumping hills (30 and 90 m). APPLICATIONS: The constructed Systems are currently used for several research projects and combined with simultaneous multichannel EMG recordings and 3 D kinematics. The platform of x-c skiing is utilized to understand in more detail the distribution of force production between legs and arms when the conditions of slope, speed, waxing, skis, poles, and snow are varied in a controlled manner. Examples of the findings will be given in the formal lecture. The systematic research in skijumping is expected to increase further understanding of the take off force production with possibilities for development of new techniques.
© Copyright 2007 4th International Congress on Science and Skiing. Published by University of Salzburg. All rights reserved.