INSIDE/OUTSIDE FORCE RATIO AND SKI CHATTER IN SLALOM SKIING ...

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• Publié par: ubitolus
• Nombre de lectures: 116
• Langue: Français

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INSIDE/OUTSIDE FORCE RATIO AND SKI CHATTER IN SLALOM SKIING  Marjaana Lappi, Robert C. Reid, Per Haugen, Gerald Smith Norwegian School of Sport Sciences, Oslo, Norway email: [e-mail]  INTRODUCTIONcourses and Pearsons correlation to assess the  relationshipbetween chatter and force distribution. Although skiers must move laterally to balance against the ground reaction forces (GRF) during turning, they can control the force distribution between the inside and the outside ski through fine- tuning of lateral balance [1]. This force distribution is important for performance, yet it is a topic of debate in coaching circles.  Traditional philosophies describe a lateral balance where the GRF loading occurs predominantly on the outside ski. However, with recent developments in equipment, philosophies have emerged promoting a more even distribution. While this may reduce ski-snow friction when carving, it may also result in greater skidding and chatter. The purpose of this study was to describe and compare ground reaction forces in slalom skiing between two courses typical of competition.Figure 1. Datalogging was accomplished with a  portableacquisition system carried in a small METHODSbackpack. Cables to the insole system were routed  underneatha skier's standard suit. Nine male Norwegian skiers (body weight 859 ± 71 N) and FIS ranked between 165 and 705 (2007/08) were tested over 3 consecutive days. Kinetic characteristics were analyzed for 2 rhythmical course settings with linear distances of 10 and 13 m between gates. The middle 10 turns of each trial were analyzed to determine GRF using 50 Hz plantar pressure insoles (Novel GmbH, Germany) and associated data logging instrumentation shown in Figures 1 & 2.  Right and left turns were separately analyzed due to differences in the side-to-side slope gradient. Inside/Outside force ratio was calculated based on force impulse during each turn. The mean residual between raw force measurements and a smoothed force-time curve (cut-off frequency 5 Hz) was usedFigure 2.Data were collected under simulated race to quantify chatter for each ski. Repeated measuresconditions during a glacier training camp with hard ANOVA was used to compare turn directions andsnow surface conditions comparable to competition.