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.