INTRODUCTION: Alpine ski racing is a complex sport in which energy dissipation is one of the crucial performance predicting parameters (Supej et al., 2010). The main factors in energy dissipation are air drag and ski-snow friction. To our knowledge, air drag cannot be directiy measured during skiing. Therefore, in order to be able to understand the performance differences that can be measured in technical skiing disciplines, it is of interest to examine the size of the differences in air drag among elite ski racers. METHOD: Ten elite alpine skiers were measured in a wind tunnel. Each of the subjects repeated three positions (low, mid and high) five times at four different velocities: 20, 40, 60 and 80 km-h"1. Air drag was measured using a force platform and the skier's posture was analyzed using camcorder-based 2D kinematics. Thereafter, the skiers' cross-sectional area and body composition were measured using an iDXA scan. To determine the product "cross sectional area * drag coefficient (Cd*S)", the quadratic drag equation was used. The Cd*S was normalized with the skier's mass and cross-sectional area of the fully extended body posture. Linear regression (y=k*x+n) was used to examine relationships between the skiers' relative Cd*S and their relative shoulder heights at different positions and air flow velocities. RESULTS: Slope k and y-intercept n values obtained from the linear regression analysis for the skiers are presented in Fig. 1. Visually, two different groups were observed, where three skiers demonstrated better values. The linear regression parameters k and n showed no correlation with 1) body weight, 2) skier body height or 3) cross-sectional area. DISCUSSION: The differences among elite skiers' air drag were rather high. No correlation with body composition was found. An interesting finding was that the three skiers with better Cd*S vs. posture were all ranked among the top four according to FIS ranking in the investigated group of skiers in the current study. CONCLUSION: The results showed that air drag among skiers was different and was related to FIS ranking. Therefore, when examining the skiers' performances and energy dissipation, their body posture should be considered in addition to how the skis are guided.
© Copyright 2010 Book of Abstracts. 5th International Congress on Science and Skiing, Dec. 14 - 19, 2010, St. Christoph am Arlberg. Veröffentlicht von University of Salzburg, Interfakultärer Fachbereich Sport- und Bewegungswissenschaft/USI. Alle Rechte vorbehalten.