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Characterization of course and terrain and their effect on skier speed in World Cup alpine ski racing.

Gilgien M, Crivelli P, Spörri J, Kröll J, Müller E - PLoS ONE (2015)

Bottom Line: In giant slalom the horizontal gate distance increased with terrain inclination, while super-G and downhill did not show such a connection.Skier speed decreased with increasing steepness of terrain in all disciplines except for downhill.In steep terrain, speed was found to be controllable by increased horizontal gate distances in giant slalom and by shorter gate distances in giant slalom and super-G.

View Article: PubMed Central - PubMed

Affiliation: Norwegian School of Sport Sciences, Department of Physical Performance, Oslo, Norway.

ABSTRACT
World Cup (WC) alpine ski racing consists of four main competition disciplines (slalom, giant slalom, super-G and downhill), each with specific course and terrain characteristics. The International Ski Federation (FIS) has regulated course length, altitude drop from start to finish and course setting in order to specify the characteristics of the respective competition disciplines and to control performance and injury-related aspects. However to date, no detailed data on course setting and its adaptation to terrain is available. It is also unknown how course and terrain characteristics influence skier speed. Therefore, the aim of the study was to characterize course setting, terrain geomorphology and their relationship to speed in male WC giant slalom, super-G and downhill. The study revealed that terrain was flatter in downhill compared to the other disciplines. In all disciplines, variability in horizontal gate distance (gate offset) was larger than in gate distance (linear distance from gate to gate). In giant slalom the horizontal gate distance increased with terrain inclination, while super-G and downhill did not show such a connection. In giant slalom and super-G, there was a slight trend towards shorter gate distances as the steepness of the terrain increased. Gates were usually set close to terrain transitions in all three disciplines. Downhill had a larger proportion of extreme terrain inclination changes along the skier trajectory per unit time skiing than the other disciplines. Skier speed decreased with increasing steepness of terrain in all disciplines except for downhill. In steep terrain, speed was found to be controllable by increased horizontal gate distances in giant slalom and by shorter gate distances in giant slalom and super-G. Across the disciplines skier speed was largely explained by course setting and terrain inclination in a multiple linear model.

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Illustration of terrain transition apex determination and the distance calculation between terrain transition apex and gate.The skier trajectory is shown in red with the deflection points of the trajectory (DP). The DPs were projected (pDP) normal onto the DTM (profile in dark grey) as well as the skier trajectory. The two pDPs and gravity span a plane. The terrain transition apex is where the arrows meet. The arrow with the dashed line represents the maximal distance to the vector between the pDPs. The solid arrow indicates the distance between the terrain apex and the gate (DTTG).
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pone.0118119.g005: Illustration of terrain transition apex determination and the distance calculation between terrain transition apex and gate.The skier trajectory is shown in red with the deflection points of the trajectory (DP). The DPs were projected (pDP) normal onto the DTM (profile in dark grey) as well as the skier trajectory. The two pDPs and gravity span a plane. The terrain transition apex is where the arrows meet. The arrow with the dashed line represents the maximal distance to the vector between the pDPs. The solid arrow indicates the distance between the terrain apex and the gate (DTTG).

Mentions: It was calculated how far gates were set from terrain transition (concave and convex) apices. Convex terrain transitions are terrain transitions where the terrain is bulging outward (bump). Concave terrain transitions are transitions where the terrain is hollowed inward (compression). The apex point of a terrain transition was calculated following a specific procedure: (1) The deflection points (DP) of the skier trajectory before and after the gate (i) were projected normal to the DTM (pDP) and a plane was spanned by the pDPs and gravity; (2) The projection of the skier trajectory onto the DTM (PS) was projected onto the plane spanned by pDP and gravity. The maximal distance of the projected PS to the vector between the two pDP was defined as the terrain transition apex; (3) The distance from the terrain transition apex to the gate (i) was calculated and named (DTTG convex or DTTG concave). The calculation procedure for the distance from a terrain apex to the corresponding gate is illustrated in Fig. 5. The median distance and interquartile range (IQR) of the distance were calculated both for all data and for only the DTTG which were smaller than 10m for both convex and concave terrain transitions.


Characterization of course and terrain and their effect on skier speed in World Cup alpine ski racing.

Gilgien M, Crivelli P, Spörri J, Kröll J, Müller E - PLoS ONE (2015)

Illustration of terrain transition apex determination and the distance calculation between terrain transition apex and gate.The skier trajectory is shown in red with the deflection points of the trajectory (DP). The DPs were projected (pDP) normal onto the DTM (profile in dark grey) as well as the skier trajectory. The two pDPs and gravity span a plane. The terrain transition apex is where the arrows meet. The arrow with the dashed line represents the maximal distance to the vector between the pDPs. The solid arrow indicates the distance between the terrain apex and the gate (DTTG).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4356573&req=5

pone.0118119.g005: Illustration of terrain transition apex determination and the distance calculation between terrain transition apex and gate.The skier trajectory is shown in red with the deflection points of the trajectory (DP). The DPs were projected (pDP) normal onto the DTM (profile in dark grey) as well as the skier trajectory. The two pDPs and gravity span a plane. The terrain transition apex is where the arrows meet. The arrow with the dashed line represents the maximal distance to the vector between the pDPs. The solid arrow indicates the distance between the terrain apex and the gate (DTTG).
Mentions: It was calculated how far gates were set from terrain transition (concave and convex) apices. Convex terrain transitions are terrain transitions where the terrain is bulging outward (bump). Concave terrain transitions are transitions where the terrain is hollowed inward (compression). The apex point of a terrain transition was calculated following a specific procedure: (1) The deflection points (DP) of the skier trajectory before and after the gate (i) were projected normal to the DTM (pDP) and a plane was spanned by the pDPs and gravity; (2) The projection of the skier trajectory onto the DTM (PS) was projected onto the plane spanned by pDP and gravity. The maximal distance of the projected PS to the vector between the two pDP was defined as the terrain transition apex; (3) The distance from the terrain transition apex to the gate (i) was calculated and named (DTTG convex or DTTG concave). The calculation procedure for the distance from a terrain apex to the corresponding gate is illustrated in Fig. 5. The median distance and interquartile range (IQR) of the distance were calculated both for all data and for only the DTTG which were smaller than 10m for both convex and concave terrain transitions.

Bottom Line: In giant slalom the horizontal gate distance increased with terrain inclination, while super-G and downhill did not show such a connection.Skier speed decreased with increasing steepness of terrain in all disciplines except for downhill.In steep terrain, speed was found to be controllable by increased horizontal gate distances in giant slalom and by shorter gate distances in giant slalom and super-G.

View Article: PubMed Central - PubMed

Affiliation: Norwegian School of Sport Sciences, Department of Physical Performance, Oslo, Norway.

ABSTRACT
World Cup (WC) alpine ski racing consists of four main competition disciplines (slalom, giant slalom, super-G and downhill), each with specific course and terrain characteristics. The International Ski Federation (FIS) has regulated course length, altitude drop from start to finish and course setting in order to specify the characteristics of the respective competition disciplines and to control performance and injury-related aspects. However to date, no detailed data on course setting and its adaptation to terrain is available. It is also unknown how course and terrain characteristics influence skier speed. Therefore, the aim of the study was to characterize course setting, terrain geomorphology and their relationship to speed in male WC giant slalom, super-G and downhill. The study revealed that terrain was flatter in downhill compared to the other disciplines. In all disciplines, variability in horizontal gate distance (gate offset) was larger than in gate distance (linear distance from gate to gate). In giant slalom the horizontal gate distance increased with terrain inclination, while super-G and downhill did not show such a connection. In giant slalom and super-G, there was a slight trend towards shorter gate distances as the steepness of the terrain increased. Gates were usually set close to terrain transitions in all three disciplines. Downhill had a larger proportion of extreme terrain inclination changes along the skier trajectory per unit time skiing than the other disciplines. Skier speed decreased with increasing steepness of terrain in all disciplines except for downhill. In steep terrain, speed was found to be controllable by increased horizontal gate distances in giant slalom and by shorter gate distances in giant slalom and super-G. Across the disciplines skier speed was largely explained by course setting and terrain inclination in a multiple linear model.

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