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Relationship between Glide Speed and Olympic Cross-Country Ski Performance

Glenn M. Street and Robert W. Gregory

While the scientific literature has confirmed the importance of high maximal aerobic power to successful cross-country skiing performance, the same cannot be said of skiing technique or gliding characteristics of skis. The purpose of this study was to determine whether glide speed was related to Olympic race performance. Male competitors in the 50-km freestyle event were videotaped during the 1992 Winter Olympic Games. Glide speeds of the entire field were measured through a 20-m flat section at the bottom of a 150-m, 12° downhill. A significant correlation (r = -.73) was found between finish time and glide speed, showing that the more successful competitors tended to have faster glide speeds through this section of the course. A predictive model of glide speed suggested that the faster glide speeds were due primarily to differences in friction. There was little evidence to suggest that differences in air drag, body mass, or initial speed accounted for the major differences in glide speeds.

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Measurement of Skier-Generated Forces during Roller-Ski Skating

Glenn M. Street and Edward C. Frederick

This paper describes a system that was developed to measure ski pole and roller-ski reaction forces in three dimensions during roller-ski skating. Uni-axial force transducers mounted in the right and left ski poles measure axial loading of the poles. Six transducers in one roller-ski measure biaxial loads beneath the foot. A remote computer stores the amplified transducer signals transmitted from the skier through 100 m cables. Three-dimensional video-graphy determines the orientations of the poles and roller-ski in order to resolve the resultant poling and skating forces into three components. Calibration data suggest that the resolution of the force measurement system is ±3 to 9% of the actual poling and skating forces, respectively. Sample data are presented from a VI skating trial during roller-skiing. These data provide the first glimpse at the major functions of the upper and lower body during roller-ski skating and show how the tool could be used to examine the size and effectiveness of skier-generated forces.

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Vaults Performed by Female Olympic Gymnasts: A Biomechanical Profile

Richard C. Nelson, Ted S. Gross, and Glenn M. Street

The purpose of this report was to provide a model analysis of biomechanical films taken during the women's gymnastic vaulting events of the 1984 Los Angeles Olympic Games. Although a majority of the optional vaults were filmed, only the 16 vaults performed by the competitors in the individual championships were examined. The analysis included calculations of temporal, spatial, and velocity parameters as the gymnast's center of mass moved through four phases of the vault. The phases were identified as Reuther board contact, prehorse flight, horse contact, and posthorse flight. A representative profile of a female gymnast competing in the Games was compiled based on these parameters. This profile indicated that the gymnasts were much smaller than the average population, efficient in the use of the Reuther board and the horse to reach and maintain CM velocities necessary to complete the vault, and agile enough to perform complex airborne rotations during an average posthorse flight duration of .80s.

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Kinematic Analysis of Skating Technique of Olympic Skiers in the Women's 30-km Race

Robert W. Gregory, Sean E. Humphreys, and Glenn M. Street

The women's 30-km freestyle cross-country race at the 1992 Winter Olympic Games was selected to determine the kinematic differences between more and less successful skiers. Three-dimensional filming techniques were used to capture the movement patterns on level terrain of 8 skiers who placed in the top 50% (Group 1) and 8 skiers who placed in the bottom 50% (Group 2) of the field. The mean cycle velocity for Group 1 was significantly faster (p < .005) than the velocity for Group 2. Significant correlations (p < .05) were found between race velocity and cycle velocity (r = .89) and between cycle length and cycle rate (r = -.82). Group 1 had significantly greater (p < .03) weak-side elbow flexion at pole plant, as well as less (p < .01) weak-side elbow extension and more (p < .05) trunk flexion during poling. The mean cycle velocity differences between Groups 1 and 2 may have been the result of smaller resistive and/or larger propulsive forces.