PROCEEDINGS OF THE 29. 11. 1. 12. 2017 Brno, Czech Republic
11 th INTERNATIONAL CONFERENCE ON KINANTHROPOLOGY Sport and Quality of Life Faculty of Sports Studies Masaryk University in collaboration with Faculty of Kinesiology University of Zagreb Conference was held under the auspices of the Ministry of Education, Youth and Sport of the Cezch Republic 29 th November 1 st December 2017 Brno, Czech Republic http://conference.fsps.muni.cz/
SCIENTIFIC COMMITTEE Martin Zvonař, Masaryk University, Czech Republic; Gheorghe Balint, Vasile Alecsandri, University of Bacău, Romania; Viktor Bielik, Comenius University in Bratislava, Slovakia; Václav Bunc, Charles University, Czech Republic; Anita Hökelmann, Otto von Guericke, University of Magdeburg, Germany; Emanuel Hurych, Masaryk University, Czech Republic; Daniel Jandačka, University of Ostrava, Czech Republic; Damir Knjaz, University of Zagreb, Croatia; Matthieu Lenoir, University of Ghent, Belgium; Josef Mitáš, Palacký University Olomouc, Czech Republic; Tomáš Perič, Charles University, Czech Republic; Rado Pišot, University of Primorska, Slovenia; Hana Válková, Masaryk University, Czech Republic ORGANIZING COMMITTEE Martin Zvonař, Natalija Babić, Roman Drga, Katarína Peterková, Pavlína Roučová, Zuzana Sajdlová REVIEWERS Václav Bunc, Viktor Bielik, Ján Cvečka, Ivan Čillík, Fadij Eminovic, Dita Hlavoňová, Iva Hrnčiříková, Emanuel Hurych, Alexandar Ignjatovic, Daniel Jandačka, Marcela Janíková, Radim Jebavý, Aleš Kaplan, Eva Kohlíková, Matthieu Lenoir, Brian Minikin, Josef Mitáš, Jana Nová, Piotr Olesniewicz, Tomáš Perič, Rado Pišot, Martin Pupiš, Oldřich Racek, Zdenko Reguli, Pavel Ružbarský, Aleš Sekot, Alena Skotáková, Lenka Svobodová, Pavel Vacenovský, Pavlína Vaculíková, Eva Valkounová, Hana Válková, Marian Vanderka, Tomáš Vencúrik, Michal Vičar, Michal Vít EDITORS Martin Zvonař, Zuzana Sajdlová TECHNICAL EDITORS Michal Huvar, Hana Pilarčíková
BIOMECHANICAL FIELD STUDY OF SLALOM TURN DURING SE- COND RUN SNOW QUEEN TROPHY RACE Cigrovski Vjekoslav, Antekolović Ljubomir, Zadravec Mateja, Bon Ivan University of Zagreb, Faculty of Kinesiology Abstract Slalom is a challenging alpine ski discipline from both tactical and technical perspective. Biomechanical factors influence the tactics employed during the race and can affect success. We performed biomechanical field study investigating velocity at different sections of slalom turn, angles of lower extremity during turn performance and their relation to projection of centre of mass during FIS World Cup Race Snow Queen Trophy. Kinematic analysis of slalom turn was performed to compare the correlations between angles in joints of lower extremities, distance of centre of mass during different segments of turn and velocity of skiing during turn in competitor level skiers. The Ariel Performance Analysis System was used to calculate the 3D kinematic data for 30 elite alpine skiers participating in the second run. Results suggest highest variability between competitors in velocities achieved during turn initiation. Moreover, we found correlation between competitors velocity during turn initiation and angle in the knee joint (r=0,56). Additionally, velocity during initial phases of turn correlated with centre of mass with respect to inner ankle joint (r=0,63), as well as with outer ankle joint (r=0,58). Moreover, angles between upper and lower leg correlated significantly with velocity during all phases of slalom turn, while we found no correlation whatsoever between competitors upper leg and core and velocity. Significant correlation was also seen between velocity during all three phases of ski turn and centre of mass during middle part of the turn in relation to both inner and outer ankle joint. Our data suggest that competitors with lower velocity at the beginning of the turn opted for a less direct trajectory. But due to configurational differences and different ways gates are positioned through entire race, competitor is not able to use the same tactics through an entire slalom race, so velocity over one turn might not have an overwhelming influence on the velocity of the race in a whole. To conclude, many different biomechanical factors influence the performance during slalom race and competitor must take into account intricate interactions between them under different conditions to minimize the descent time. Key words: slalom, kinematic, velocity of skiing, line of skiing, skiing technic 19
Introduction The difference between medal winning places in highly competitive slalom discipline of alpine skiing is often measured in fractions of a second. These small winning margins accentuate the need for a better understanding of factors influencing performance. Biomechanics of slalom skiing imposes as an important field of investigation (Hebert-Losier et al., 2014). Racing tactics that current elite alpine skiers apply relates to the choosing of specific trajectory while passing through the gates. Choosing the right trajectory enables reaching higher velocities or keeping the existing speed of skiing (Cigrovski & Matković, 2015). To shorten the route between the gates, competitors on the steep parts often choose direct trajectory. Mentioned tactics together with alpine ski technique are the main factors underpinning the speed of ski sliding (Federolf et al., 2013). In the recent years, slalom discipline is specific due to more narrow corridor of turns and shortening of the ski arches. This means that competitors are faster and that they have minimized the path between the gates (LeMaster, 2010). Choosing the right moment in which competitor will initiate the new turn or will pass from one turn to another for the consequence has ideal speed of ski sliding and might influence the success of ski performance (Hebert-Losier et at., 2014). That is why each competitor before ski race divides slalom track into several segments and decides on the trajectories while passing through the gates. Supej and Cernigoj (2006) specifically divided alpine ski race track into nine segments and shown how performance of first three competitors differed in ski tactics in all the mentioned ski sections. Because of different tactics in different segments, competitors differ in ski technique and adjust ski technique to the trajectory choice. Differences in ski technique can be followed by observation of competitors joints and body segments as well as by ski movements during particular stages of the ski turn (Hraski & Hraski, 2009; Reid et al., 2009; Kipp et al., 2010). By analysing the angles in the competitors joints as well as the projections of the body s centre of gravity in certain parts of the turn, it is likely possible to predict ways of making turns regarding ski techniques and tactics. Methods Participants: 30 male professional skiers, mean age 27.12±1.15 years were included in the investigation. They were tested during slalom competition FIS Ski World Cup Snow Queen Trophy (Sljeme, Croatia). Variables: Kinematic variables that were used to describe slalom turn included: velocity at the beginning of slalom turn (VB), measured time at the beginning of ski 20
turn in ms ¹, velocity in the middle part of the slalom turn (VM), measured time during central phase of ski turn in ms ¹, velocity at the end of slalom turn (VE), measured time at the end of ski turn in ms ¹, knee angle (KA), measures angle between upper and lower leg in, hip angle (HA), measures angle between upper leg and core in, centre of mass at the beginning of slalom turn in relation to inner ankle joint (COMIAB), represents the difference between projection of centre of mass at the beginning of the turn and ankle joint of the inner leg measured in cm, centre of mass at the beginning of slalom turn in relation to outer ankle joint (COMOAB), represents the difference between projection of centre of mass during beginning of ski turn in relation to outer leg measured in cm, centre of mass at the middle of the slalom turn in relation to inner ankle joint (COMIAM), represents the difference between projection of centre of mass and inner leg ankle joint measured in cm, centre of mass at the middle of the slalom turn in relation to outer ankle joint (COMOAM), represents the difference between projection of centre of mass and outer leg ankle joint measured in cm, centre of mass at the end of slalom turn in relation to inner ankle joint (COMIAE), represents the difference between projection of centre of mass and inner leg ankle joint measured in cm, centre of mass at the end of slalom turn in relation to outer ankle joint (COMOAE), represents the difference between projection of centre of mass and outer leg ankle joint measured in cm. Research protocol: We analysed some biomechanical aspects during one slalom turn. Data for kinematic analysis was filmed during slalom competition by two DV cameras (Sony HDR-HC9E), with 50 photos per second and with shutter speed 1/500 sec. The space calibration was done with cube (180 cm x 180 cm x 180 cm) filmed after competition on the position of analysed slalom turn. Position of cameras is shown in Figure 1. Figure 1. Camera positions 21
Statistical methods: The Ariel Performance Analysis System (APAS, Ariel Dynamics inc., USA) was used to analyse video recordings and calculate the 3D kinematic data. Correlations between the analysed variables were tested by correlation analysis. The Statistica ver. 7.1 (StatSoft, Inc., 2006) was used. All competitors of the 2 nd slalom run were filmed by two DV cameras (Sony HDR-HC9E) operating at 50 fps with shutter speed of 1/500 sec. The space calibration was done with cube (180 cm x 180 cm x 180 cm) filmed after competition on the position of analysed slalom turn. Results and discussion Results of the descriptive statistics are presented in Table 1. Table 1. Descriptive statistics Legend: VB-velocity at the beginning of slalom turn; VM velocity in the middle part of the slalom turn; VE-velocity at the end of slalom turn; KA-knee angle; HA-hip angle; COMIAB-centre of mass at the beginning of slalom turn in relation to inner ankle joint; COMOAB-centre of mass at the beginning of slalom turn in relation to outer ankle joint; COMIAM-centre of mass at the middle of the slalom turn in relation to inner ankle joint; COMOAM-centre of mass at the middle of the slalom turn in relation to outer ankle joint; COMIAE- centre of mass at the end of slalom turn in relation to inner ankle joint; COMOAE-centre of mass at the end of slalom turn in relation to outer ankle joint 22
Correlation analyses are presented in Table 2. Table 2. Correlation between analysed variables Variable VB VM VE KA HA COMIAB COMOAB COMIAM COMOAM COMIAE COMOAE VB 1 0,98* 0,97* 0,56* 0,42 0,63* 0,58* 0,64* 0,62* -0,11-0,09 VM 1 0,99* 0,53* 0,37 0,54* 0,49 0,58* 0,56* -0,17-0,15 VE 1 0,5* 0,32 0,51* 0,42 0,51* 0,5* -0,21-0,2 KA 1 0,92* 0,07 0,57* 0,2 0,14-0,59* -0,53* HA 1 0,23 0,77* 0,39 0,39-0,28-0,2 COMIAB 1 0,77* 0,94* 0,95* 0,66* 0,67* COMOAB 1 0,87* 0,83* 0,32 0,39 COMIAM 1 1 0,6* 0,65* COMOAM 1 0,64* 0,67* COMIAE 1 0,99* COMOAE 1 Legend: VB-velocity at the beginning of slalom turn; VM velocity in the middle part of the slalom turn; VE-velocity at the end of slalom turn; KA-knee angle; HA-hip angle; COMIAB-centre of mass at the beginning of slalom turn in relation to inner ankle joint; COMOAB-centre of mass at the beginning of slalom turn in relation to outer ankle joint; COMIAM-centre of mass at the middle of the slalom turn in relation to inner ankle joint; COMOAM-centre of mass at the middle of the slalom turn in relation to outer ankle joint; COMIAE- centre of mass at the end of slalom turn in relation to inner ankle joint; COMOAE-centre of mass at the end of slalom turn in relation to outer ankle joint; * - significant at p=0.05 Data suggest variations in velocity at the beginning of slalom turn ranging from 9,65 to 17,93 ms ¹ (Mean=14,4 ms ¹), during middle part of the turn from 11,4 to 13,91 ms ¹ (Mean=13,4 ms ¹), while velocity range during final parts of the slalom turn ranged from 12,21 to 14,97 ms ¹ (Mean=13,1 ms ¹). The greatest variability in competitors velocity was seen during slalom turn initiation, where the differences between competitors in the filmed segment of slalom turn were greatest. According to Federolf and coworkers, the difference in velocity between competitors persisted all through phases of the slalom turn (2013). Our data suggest that competitors with lower velocity at the beginning of the turn opted for a less direct trajectory. Similar observation was reported by Lešnik and Žvan (2007), where skiing velocity generally increases as the skiing line decreases. In the present investigation, we measured skiers velocity during three phases of ski turn (during turn initiation, at the middle part and at the end of turn). The greatest correlation was seen between competitors velocity during turn initiation and angle in the knee joint (r=0,56). Additionally, velocity 23
during initial phases of turn correlated with centre of mass with respect to inner ankle joint (r=0,63), as well as with centre of mass with respect to outer ankle joint (r=0,58). Angles in the knee joint varied between 86 and 104 (Mean=95 ), while angles in the hip joint varied between 77 and 107 (Mean=91 ). Analysed angles between upper and lower leg correlated significantly with velocity during all phases of slalom turn, while we found no correlation whatsoever between competitors upper leg and core and velocity. On the contrast, results by Hraski and Hraski (2009) measuring angles between core and angles in different joints suggest that higher angles in the hip joint correlated with higher velocity and better performance during slalom turn. Centre of mass at the initiation of slalom turn varied from 0,1 to 19 cm (Mean 4,5 cm) in relation to inner leg ankle joint, and 9 to 35 cm (Mean 21,7 cm) in relation to outer leg ankle joint. Centre of mass at the middle section of ski turn varied 0,6 to 16 cm (Mean 8,4 cm) in relation to inner ankle joint, and 0,4 to 15 cm (Mean 6,5 cm) in relation to outer leg ankle joint. Centre of mass at the end of the slalom turn varied between-32 to -4 cm, (Mean=-21,3 cm) in relation to inner ankle joint, and between -31 and -3 cm, (Mean=-15,7 cm) in relation to outer leg ankle joint. Significant correlation was seen exclusively between velocity during all three phases of ski turn and centre of mass during middle part of the turn in relation to both inner and outer ankle joint. Kinematic analysis of slalom turn was performed to compare the correlations between angles in joints of lower extremities, distance of centre of mass during different segments of turn and velocity of skiing during turn in competitor level skiers. This enables analysis of ski technique and tactics relating to choosing different trajectories during ski turns. Mentioned was also analysed in our previous investigation where we found no significant difference between distances between skiers body from the gate compared to velocity of skiing in the analysed turn (Antekolovic et al., 2015). We can argue that one turn did not have an overwhelming influence on the velocity of the race in a whole. Due to configurational differences and different ways gates are positioned through entire race, competitor is not able to use the same tactics through an entire slalom race. Usually accepted is that maintenance of high velocities is an important determinant of ski performance, regardless of ski trajectory, technique or approach to turn execution (Hebert-Losier et at., 2014). Several studies reported that more rapid turns were initiated further from the gate, and completed closer to the gate and were longer, allowing greater acceleration from the gate and straighter skiing after the gate (Supej, 2008; Sporri et al., 2010). As important are the current snow conditions during race which affect competitors tactics. All the mentioned suggests that many different biomechanical factors influence the performance during slalom race and that intricate interactions between them and under different conditions must be used by competitor to minimize the descent time. Slalom racing is a complex and challenging 24
discipline from both technical and tactical perspectives. Biomechanical components of slalom turn are important factor in performance of elite competitors and may be one of the determining factors of success. A limitation of this study is analysis of skiing performance over one gate, so generalization of findings must be done with caution to determine whether performance of one turn accurately reflects performance of an elite skier across the series of gates and whether instantaneous performance can be maintained throughout an entire race. But in biomechanical field studies, video-based systems are widely used and considered reliable tools. References Antekolović, Lj., Cigrovski, V., Horgas A. (2015). Some biomechanical characteristics of slalom turn during race of elite alpine skiers. Proceedings of the «10th International conference on kinanthropology. (Eds. M. Zvonař, Z. Sajdlová), Brno 18.-20.11.2015. pp.456-461. Brno: Masaryk University, Faculty of sport studies. Cigrovski, V., & Matković, B. (2015). Skiing technique carving. Zagreb (CRO): University of Zagreb, Faculty of Kinesiology. Federolf, P., Reid R., Gilgien, M., Haugen, P., Smith, G. (2013). Technique analysis in alpine ski racing: what motions of a skier cause a decline in speed? In: Book of Abstracts 6th international congress on Science and skiing. (Eds. E. Műller, J. Kroll, S. Lindinger, J. Pfusterschmied, T. Stoggl), pp. 73. Salzburg: University of Salzburg. Hébert-Losier, K., Supej, M., Holmberg, H.C. (2014). Biomechanical factors influencing the performance of elite Alpine ski racers. Sports Medicine. 44(4):519-533. Hraski Z., Hraski, M. (2009). Influence of the skiers body geometry on the duration of the giant slalom turn. In: 4th international congress on Science and skiing. (Eds. Muller E, Lindinger S, Stoggl T) pp. 252-259. London: Meyer & Meyer Sport. Kipp. R., Reid, R., Gilgien, M., Haugen, P., Smith, G. (2010). Relative contributions of leg angles to ski edging during a slalom ski turn. In: Book of Abstracts 5th international congress on Science and skiing. (Ed. E. Műller, S. Lindinger, T. Stoggl, J. Pfusterschmied), p. 129. Salzburg: University of Salzburg. 25
Lešnik, B., Žvan, M. (2007). The best slalom competitors-kinematic analysis of tracks and velocities. Kinesiology, 39(1):40-48. LeMaster, R. (2010). Ultimate skiing. Champaign, IL.: Human Kinetics. Sporri, J., Kroll, J., Schiefermuller, C., Muller E. (2010). Line characteristics and performance in gigant slalom. In: Book of Abstracts 5th international congress on Science and skiing. (Eds. E. Műller, S. Lindinger, T. Stoggl, J. Pfusterschmied), pp. 57. Salzburg: University of Salzburg. Supej, M., Cernigoj, M. (2006). Relations between different technical and tactical approaches and overall time at men s world cup giant slalom races. Kinesiologia Slovenica, 12(2):59 68. Supej, M. (2008). Differential specific mechanical energy as a quality parameter in racing alpine skiing. Journal of Applied Biomechanics, 24(2): 121-129. Reid, R., Gilgien, M., Moger, T., Tjorhom, H., Haugen, P., Kipp, R., Smith, G. (2009). Turn characteristics and energy dissipation in slalom. In: 4th international congress on Science and skiing. (Eds Muller E, Lindinger S, Stoggl T) pp. 419-429. London: Meyer & Meyer Sport. 26