Mechanical energy dissipation, movement, and performance characteristics in competitive alpine skiing

In 2005, Supej et al. [1] introduced a method of computing the mechanical energy losses of a skier to his surroundings as a measure of turn quality. Characterizing how elements of technique influence energy loss may help our understanding of how technique and performance relate. The purpose of this study was to describe the time-course of ski and center of mass (COM) motion characteristics and their relationships to both mechanical energy dissipation (EDISS) and performance in slalom. METHODS: Six members of the Norwegian menÂ’s national team were analyzed through 2 turns during race simulations on 2 courses set with 10 and 13 m distances between gates. 3-D positions were captured from 4 cameras and control points distributed near the course [2]. Skier mechanical energy was determined knowing COM velocity and altitude. EDISS was calculated by differentiating mechanical energy with respect to altitude [1]. Pearson product moment correlation coefficients (r) were calculated to assess the relationship of instantaneous measures of COM fore/aft position and outside ski attack angle (Gamma;SKI) with EDISS. Average fore/aft position, fore/aft range of motion, amplitude of COM vertical motion and average initiation phase Gamma;SKI were compared to performance time using Spearman rank correlation coefficients (Rho;). RESULTS: Skier fore/aft position correlated strongly with both performance (Rho;=1.0) and EDISS (r=.73, p<.001) on the 10 m course but less strongly on the 13 m course (Rho;=.72, p=.10 & r =.54, p<.001, respectively). Significant correlations were observed between the amplitude of COM vertical motion and performance on both the 10 (Rho;=.83, p=.04) and 13 m (Rho;=.79, p=.06) courses, with the faster skiers having smaller amplitudes. Initiation phase Gamma;SKI was not significantly correlated to performance on either course (Rho;=.26 and .34 for the 10 and 13 m courses, respectively). Correlations between instantaneous Gamma;SKI and EDISS were r=.29 and .01 for the 10 and 13 m courses, respectively. DISCUSSION: While the time correspondence of skier fore/aft position and EDISS was high on the 10 m course, the relationship was less clear for the 13 m course. This may be related to the larger gamma;SKI observed on the 10 m course. The strong correlations on both courses between vertical displacement and time suggest that vertical motion plays an important role in performance. Since it is the ground reaction force that turns the skier, excessive unloading from the snow surface due to increased vertical motion is likely to delay turning and thus be detrimental to performance during rapid turn transitions. The low correlations between Gamma;SKI and EDISS are surprising, and suggest that though skidding may influence EDISS, other factors may play a greater role.
© Copyright 2009 14th annual Congress of the European College of Sport Science, Oslo/Norway, June 24-27, 2009, Book of Abstracts. Published by The Norwegian School of Sport Sciences. All rights reserved.

Subjects: alpine skiing analysis biomechanics energy mechanics performance factor high performance sport elite sport motor skill movement precision movement co-ordination movement characteristic
Notations: technical sports technical and natural sciences training science
Published in: 14th annual Congress of the European College of Sport Science, Oslo/Norway, June 24-27, 2009, Book of Abstracts
Editors: S. Loland, K. Boe, K. Fasting, J. Hallen, Y. Ommundsen, G. Roberts, E. Tsolakidis
Published: Oslo The Norwegian School of Sport Sciences 2009
Pages: 520
Document types: congress proceedings
Language: English
Level: advanced