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Alpine ski racing technique

On Monday, May 10th, 2010, Robert C. Reid will defend his thesis “A kinematic and kinetic study of alpine skiing technique in slalom” for the degree of philosophiae doctor (PhD) at the Department of Physical Performance, the Norwegian School of Sport Sciences, Oslo, Norway.

Bilde av slalåmløyper hvor Reid gjorde noen av sine observasjoner
Aims of the Thesis
The purpose of this research project was to identify, describe, and study aspects of alpine ski racing technique which play an important role in determining skier performance. An additional purpose was to establish the theoretical and methodological foundation for a line of future research on this topic.

A 3-dimensional, video-based photogrammetric method was implemented to capture the performances of six highly-skilled athletes during slalom race simulations on courses with 10 and 13 m linear gate distances. The resulting data were then used to examine kinematic, kinetic, and energetic questions related to ski motion, skier technique, and performance. A comparison between courses was made in the hope that understanding how skiers adapted to the differing gate distances would shed further light on the relationship between turning mechanics and performance.
Ski Motion
The results of this investigation provide observational evidence in support of current theoretical models
of ski snow interaction mechanics and may provide insight into both ski design and injury prevention issues.
Skisse av svingmekanikk
Many of the differences observed between courses in terms of ski motion, skier kinematics and skier kinetics are reminiscent of differences in carving and skidding mechanics.
Skier Kinematics
A finding of particular significance was the difference in turn cycle structure observed between courses. While the skiers’ trajectories were symmetrically distributed about the gate on the 10 m course, there was a prolonged Initiation Phase on the 13 m course, resulting in an asymmetrical trajectory about the gate. This difference in turn structure and trajectory shape may to a large degree be the result of the different gate distances and the skis’ physical properties.

Both center of mass vertical and fore/aft actions correlated well with elapsed time through the investigated sequence. A relatively strong correlation observed between center of mass fore/aft position and mechanical energy loss further indicates that this is a parameter whose role in skiing mechanics and performance should be investigated further.
Skier Mechanical Energy
A cyclical pattern of energy dissipation was observed on both courses with high dissipations occurring during the turn and low dissipations during the transition between turns. Negative dissipations—situations where skier kinetic energy increased by more than what can be attributed to changes in potential energy—were observed at the transition between turns. This may provide evidence of skiers increasing their kinetic energy through muscular work. However, these increases were small, representing less than 3 % of skier kinetic energy gains.

About 20 % of skier mechanical energy loss in the investigated situation was a result of air drag. The remaining majority of mechanical energy losses were attributed to a drag component of the snow reaction force. However, this study does provide evidence suggesting that the energy cost of gate clearance in slalom may play a significant role and needs to be accounted for in future work.
This project has provided a conceptual model of turning technique in alpine ski racing that is based on both scientific and practitioner knowledge and that can be used to guide future research efforts.
Perhaps the most important scientific contribution of this study lies in the identification of turning technique parameters which need to be better understood to further develop our knowledge of how the mechanics of turning technique relates to performance.
Bilde av Robert Reid Robert C. Reid (06.01.1971) was born in Houston, Texas. He obtained his bachelor degree in Exercise and Sport Science from the University of Utah, Salt Lake City, Utah, and his Masters degree in Exercise Physiology from the Norwegian School of Sport Sciences. He has worked as both a coach and applied sport scientist in alpine skiing at both club and national team levels in the United States and Norway. Robert began his PhD in 2004 and has been supervised by Professor Gerald Smith (Norwegian School of Sport Sciences and Utah State University).
Evaluation committee
Leader:  Prof. Dr. Elisabeth Børsheim, Department of Sports Medicine
 Norwegian School of Sport Sciences
1st Opponent:  Prof. Dr. Hermann Schwameder, Department of Sport and Sport Science Karlsruhe Institute of Technology 
2nd Opponent:  Prof. Dr. Christopher A. Brown, Mechanical Engineering Department Worcester Polytechnic Institute
10.15 – 11.00 Trial Lecture: “Advantages, challenges and limits of field studies in biomechanical research.”

13.00 – 16.00 Doctoral Defense
Both the trial lecture and doctoral defense are open to the public. The trial lecture will be streamed at nih.no.


Department for Physical Performance