SAFETY ASSESSMENT OF JUMPS IN SKI RACING
Nachbauer, W.1 , Mössner, M.2 and Schindelwig, K.1
1) Department of Sport Science, University of Innsbruck, Austria 2) Centre of Technology of Ski- and Alpine Sport
18th annual Congress of the EUROPEAN COLLEGE OF SPORT SCIENCE, 26th – 29th June 2013 2
Introduction
Statistic world cup ski racingFrom 1605 athletes of the Austrian Ski Federation winter seasons of 1995/96 to 2012/13 595 injuries - from these 237 severe(Nachbauer et al., 2013)
Landing back-weighted after jumpssecond most common skiing situation of an ACL injury (Nachbauer et al., 2013)
Accurate predictiononly with wind tunnel experiments (drawback - high costs)(Brownlie et al., 2010, Chowdhury et al., 2010)
18th annual Congress of the EUROPEAN COLLEGE OF SPORT SCIENCE, 26th – 29th June 2013 3
Goal
Develop a simulation model to predict the injury hazard of jumps in downhill ski races
Hazard measure - equivalent fall height (EFH)
Variable inclination landing area –concept of effective landing height (ELH)
Method: field measurement
18th annual Congress of the EUROPEAN COLLEGE OF SPORT SCIENCE, 26th – 29th June 2013 6
4 jumps – 145 jumps analysedSprung ins Himmelreich (SH), Panorama Sprung (PS), Mausefalle (MF), Kamelbuckel (KB)
3 Cameras20 Hz, 6 MP (Casio Exilim EX_F1)300 HZ, 0.2 MP (Casio Exilim EX_F1)
Theodolite (CTS-2B)position of cameras, gates, …
Inclinometer (Pieps 30° Plus)slope inclination
18th annual Congress of the EUROPEAN COLLEGE OF SPORT SCIENCE, 26th – 29th June 2013 5
Method: 3d reconstruction
18th annual Congress of the EUROPEAN COLLEGE OF SPORT SCIENCE, 26th – 29th June 2013 5
Method: 3d reconstruction
skier’s plane
π
ε
image coordinates
18th annual Congress of the EUROPEAN COLLEGE OF SPORT SCIENCE, 26th – 29th June 2013 7
Method: simulation model
Forces
Equation of motion – point mass
18th annual Congress of the EUROPEAN COLLEGE OF SPORT SCIENCE, 26th – 29th June 2013 7
Method: simulation model
Integration of the equation of motion Runge-Kutta scheme Δt of 0.01 s
Drag and Lift determined by parameter identification
Least squares fit the solution of the equation of motion is fitted to the measured trajectory
18th annual Congress of the EUROPEAN COLLEGE OF SPORT SCIENCE, 26th – 29th June 2013 7
Method: simulation model
Equivalent fall height (Hubbard (2008) (valid for landing area with const. inclination)
Equivalent landing height
t1t2
v2
v1
v1
v2v2-1
18th annual Congress of the EUROPEAN COLLEGE OF SPORT SCIENCE, 26th – 29th June 2013 10
Results: reconstruction accuracy
rms deviation for the ski lenght:2.2 cm
max. difference between cameras:11.8 cm for center of mass
Eq
18th annual Congress of the EUROPEAN COLLEGE OF SPORT SCIENCE, 26th – 29th June 2013 10
Results: high speed video of landing movement
18th annual Congress of the EUROPEAN COLLEGE OF SPORT SCIENCE, 26th – 29th June 2013 7
Method: jump parameter
Jump v0 (km/h) α0- β0 (°) D (m2) L (m2) EFH (m)
SH 86 (77-91)
2.3 (0.6-3.6)
0.32 (0.23-0.61)
0.06 (-0.06-0.16)
0.78 (0.45- 1.04)
PS 92 (85-99)
0.1 (-2.1-1.5)
0.43 (0.33-0.52)
0.07 (-0.01-0.12)
0.62 (0.35- 1.01)
MF 93 (86-97)
2.1 (0.7-4.7)
0.46 (0.35-0.58)
0.02 (-0.05-0.06)
0.89 (0.62- 1.37)
KB 109(103-116)
-0.1 (-2.7 - 2.4)
0.42 (0.27-0.65)
0.01 (-0.05-0.06)
1.98 (0.92 - 3.22)
α0- β0 3
0-3
18th annual Congress of the EUROPEAN COLLEGE OF SPORT SCIENCE, 26th – 29th June 2013 10
Results: EFH take-off angle – approach speed
80 85 90 95 100 105 1100
0.5
1
1.5
2
2.5 3° 0° -3° crit-ical m. d.
v0 (km/h)
EFH
(m)
jump „Mausefalle“
90 95 100 105 110 115 120 125 1300
0.5
1
1.5
2
2.5
3
3.5
3° 0° -3°critical value m.d.
v0 (km/h)
ELH
(m)
18th annual Congress of the EUROPEAN COLLEGE OF SPORT SCIENCE, 26th – 29th June 2013 10
Results: EFH versus ELH
90 95 100 105 110 115 120 125 1300
0.5
1
1.5
2
2.5
3
3.5
v0 (km/h)
jump „Kamelbuckel“ EFH (m) ELH (m)
18th annual Congress of the EUROPEAN COLLEGE OF SPORT SCIENCE, 26th – 29th June 2013 10
Diskussion: summary
Accurracy greatest difference of vertikal position: 118 mm error of determination of drag and lift area +/- 0.3 m²
EFH versus ELHequivalent fall height (EFH) assess the energy absorbed upon landing, if inclination of landing area is constant
equivalent landing height (ELH) is needed, if inclination of landing area is NOT constant
Simulation modela prediction of the injury hazard of a jump is possible
18th annual Congress of the EUROPEAN COLLEGE OF SPORT SCIENCE, 26th – 29th June 2013 10
Conclusion
Simulation model was developed to predict the equivalent fall height for jumps
Necessary parameters were measured for four jumps during world cup races.
Take-off angle, velocity and steepness of landing area are the most dominant factors for the equivalent fall height.
The equivalent fall height is an important measure to assess the effect of possible impact hazards and, thus, the given simulation model can be used to improve the safety for jumps in ski racing.
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