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Effect of Ski Geometry and Standing Height on Kinetic Energy: Equipment Designed to Reduce Risk of Severe Traumatic Injuries In Original article Br J Sports Med: first published as 10.1136/bjsports-2015-095465 on 23 December 2015. Downloaded from Effect of ski geometry and standing height on kinetic energy: equipment designed to reduce risk of severe traumatic injuries in alpine downhill ski racing Matthias Gilgien,1 Jörg Spörri,2 Josef Kröll,2 Erich Müller2 ▸ Additional material is ABSTRACT High speed is expected to shorten the preparation published online only. To view Background Injuries in downhill (DH) are often related time necessary for the skier to adapt to jumps and please visit the journal online 3 (http://dx.doi.org/10.1136/ to high speed and, therefore, to high energy and forces demanding course sections. High speed is also bjsports-2015-095465). which are involved in injury situations. Yet to date, no expected to increase jump length and air time, study has investigated the effect of ski geometry and resulting in an increased risk of falling.34 1Department of Physical Performance, Norwegian standing height on kinetic energy (EKIN) in DH. This Furthermore, high speed and, therefore, high 2 School of Sport Sciences, Oslo, knowledge would be essential to define appropriate kinetic energy (EKIN=1/2×mass×speed ) are likely Norway equipment rules that have the potential to protect the to increase the forces that occur at the impact in 2 Department of Sport Science athletes’ health. fall or crash situations.3 Consequently, reducing and Kinesiology, University of fi fi Salzburg, Hallein-Rif, Austria Methods During a eld experiment on an of cial EKIN can be considered a potential prevention tool, World Cup DH course, 2 recently retired world class particularly in super-G and DH.3 Correspondence to skiers skied on 5 different pairs of skis varying in width, Thus far, it is known that course setting might be Matthias Gilgien, Department length and standing height. Course characteristics, an effective preventative measure to control skier of Physical Performance, terrain and the skiers’ centre of mass position were speed and E in steep terrain in DH courses.56 Norwegian School of Sport KIN Sciences, Sognsveien 220, captured by a differential Global Navigational Satellite In addition, equipment-related measures, namely Oslo 0806, Norway; System-based methodology. EKIN, speed, ski–snow different ski geometries and standing height (ie, [email protected] friction force (FF), ground reaction force (FGRF) and ski– distance from ski base to binding plate cover), snow friction coefficient (Coeff ) were calculated and might potentially reduce E /speed, as was Accepted 3 November 2015 F KIN analysed in dependency of the used skis. hypothesised by expert stakeholders of the WC ski Results In the steep terrain, longer skis with reduced racing community.7 Yet to date, scientific knowl- – – width and standing height significantly decreased edge on DH is very limited,3 6810 and no field average EKIN by ∼3%. Locally, even larger reductions of study has assessed equipment-related, preventative EKIN were observed (up to 7%). These local decreases in measures in super-G and DH. EKIN were mainly explainable by higher FF. Moreover, Therefore, this study aimed to investigate the CoeffF differences seem of greater importance for effect of modifications in ski geometry (ski length, explaining local FF differences than the differences ski width) and standing height of DH skis on speed in FGRF. and EKIN while skiing a WC DH course. Conclusions Knowing that increased speed and EKIN likely lead to increased forces in fall/crash situations, the METHODS http://bjsm.bmj.com/ observed equipment-induced reduction in EKIN can be Measurement protocol and data collection considered a reasonable measure to improve athlete Two recently retired (10 months) male WC athletes safety, even though the achieved preventative gains are (age: 34.5±4.5 years; height: 184±2 cm; weight: rather small and limited to steep terrain. 98.5±1.5 kg) skied several runs on five different pairs of skis varying in width (W), standing height (H) and length (L). For each skier, 4 runs per ski INTRODUCTION were considered for the data analysis (ie, a total of on October 2, 2021 by guest. Protected copyright. Alpine ski racing is known to be a sport with a 40 runs). The test order of the skis was randomised high risk of sustaining severe injuries.12Injury and snow conditions were monitored. The refer- rates for World Cup (WC) athletes were found to ence ski (SKIREF) was built according to the differ among the competition disciplines, particu- International Ski Federation (FIS) equipment rules larly when calculated as injuries per 1000 runs: being valid until Winter Season 2011/2012.11 The they increased from slalom to giant slalom, super-G specifications of all other skis were defined by an Open Access and downhill (DH) with the knee as the most fre- expert group consisting of representatives of the Scan to access more 1 free content quently injured body part. However, if injury risk Ski Racing Suppliers Association (SRS), FIS Race is normalised with risk exposure time and calcu- Directors and researchers who took into consider- lated as the number of injuries per time skiing, the ation the existing scientific knowledge and practical disciplines giant slalom, super-G and DH can be experience (table 1). All prototypes were con- considered to be equally dangerous but for differ- structed by one company under the guidance of ent reasons.3 SRS, strictly adhered to the predefined geometrical With respect to the injury causes, a recent study variables (table 1) and material composition. assessing the skier biomechanics in WC alpine The biomechanical field experiment was con- To cite: Gilgien M, Spörri J, skiing found that injuries in super-G and DH are ducted on the lower part of the FIS WC DH Kröll J, et al. Br J Sports most likely due to high speeds, jumps and higher course in Åre (Sweden), directly after a women’s – Med 2016;50:8 13. workloads caused by long competition times.3 WC DH race. The first section of the course was Gilgien M, et al. Br J Sports Med 2016;50:8–13. doi:10.1136/bjsports-2015-095465 1of7 Original article Br J Sports Med: first published as 10.1136/bjsports-2015-095465 on 23 December 2015. Downloaded from Table 1 Specification of the basic geometric parameters of the Table 2 Characteristics of the course for the steep (SectionSTEEP) DH skis used for the experiments and the flat (SectionFLAT) sections of the downhill course SKIREF* SKIWH SKILH SKIWL SKIWLH Parameter Entire course Width (mm) 69 65 69 65 65 Course length (m) 1302 Standing height (mm) 50 40 40 50 40 Vertical drop (m) 402 Length (cm) 216 216 220 220 220 Number of gates ( ) 21 Mean run time (s) 50.0 *SkiREF represents the original DH racing skis according to the FIS equipment rules valid until Winter Season 2011/2012.8 DH, downhill; FIS, International Ski Federation; SKIREF, reference ski. SectionSTEEP SectionFLAT Median terrain inclination (°) −23 −15 Median gate distance (m) 84.23 61.67 steep and turning (SectionSTEEP), the second section was flat and Median horizontal gate distance (m) 35.65 12.23 less turning (SectionFLAT; figure 1). The analysis for SectionSTEEP Mean direction change from gate to gate (°) 23 11 started at the first gate where skiers reached 19.9 m/s and ended at gate number 9. The analysis of SectionFLAT started at gate 11 and ended at gate 21. – Course setting and the snow surface geomorphology were (FGRF) and ski snow friction force (FF) were calculated by the captured using static differential global navigation satellite application of a kinetic model on the CoM position, the virtual systems (dGNSS) and were reconstructed in a digital terrain pendulum model and the body extension (measurement-system 56 17 – model (DTM), as conducted in earlier studies. Each skier’s accuracy: 63N for FGRF; 42N for FF). The ski snow friction fi fi instantaneous three-dimensional position was captured by kine- coef cient (CoeffF) was calculated as the coef cient of FF and 16 matic dGNSS (50 Hz), using GPS and the Russian (GLONASS) FGRF. To compare the time series data of speed, turn radius, global navigation satellite systems, L1 and L2 signals, and was EKIN,FGRF,FF and CoeffF, between runs, parameters were spa- carried in a small backpack as described in detail in previous tially normalised based on an alternative approach specifically studies.12 13 The centre of mass (CoM) position of the skier was dedicated to the characteristics of competitive alpine DH skiing approximated using a virtual pendulum model, which was (see online supplementary data). attached to the skier’s antenna position and the intersection of the pendulum with the snow surface DTM.12 Statistical analysis The statistical analysis was conducted for skiers A and B and for Postprocessing and parameter calculations SectionSTEEP and SectionFLAT separately. For each run of each Course setting was characterised by gate distance and horizontal skier and each ski, E averages of the Section and gate distance,14 15 using the definition of double gate turns in KIN STEEP 5616 SectionFLAT were calculated. Based on these single EKIN section speed disciplines introduced in earlier studies. Skier speed, averages, participant mean±SD values were computed for all turn radius and EKIN were derived from the CoM position 12 tested skis. In addition, EKIN section averages were tested for sig- (measurement-system accuracy: 0.1 m). Ground reaction force nificant differences between the tested skis using a one-way ana- lysis of variance (ANOVA; p<0.05). For pairwise comparison, the post hoc Tukey-Kramer correction was used. To assess if the http://bjsm.bmj.com/ response to the ski intervention was similar for both skiers, the average EKIN difference between SKIREF and each ski type was compared between the skiers for each section.
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