european college of sport science

Saturday, June 27th, 2009
Scheiber P, Krautgasser S, Von Duvillard SP et al (2009) Physiological responses of older recreational alpine skiers to different skiing
modes. Europ Journal of Applied Physiology, 105(4), 551 - 558.
Seifert J, Kroell J, Mueller E (2008) The Relationship of Heart Rate and Lactate to Cumulative Muscle Fatigue during Recreational Alpine
Skiing. Journal of Strength & Conditioning Research. In Press.
THE RELATIONSHIP BETWEEN THE TIMING OF TAKE-OFF ACTION AND FLIGHT LENGTH BY USING TWO DIFFERENT
TYPES OF JUMP-DOLLS
SASAKI, T., TSUNODA, K., HOSHINO, H., MIYAKE, S.
HOKUSEI GAKUEN UNIVERSITY
Introduction: The purpose of this study is to detect the optimal timing of jump action in ski jumping. Assuming a jumper could always
produce same motions, the timing of jump action would be the most important variable for the flight distance. In this study, the jump of
the two different jump-dolls were observed on the hill model (1/100). Dolls always produce same power during jump action. Thus, the
flight distance solely depends on the timing of initiating the action. Therefore, it is possible to clarify the relationship between the timing
and the flight distance.
Methodology: Two different types of jump-dolls were developed. First doll was used two springs for producing softer power. Four springs
were set in respective joints (knees and hips) of the second types of the doll. The jump doll can reproduce the same hopping action on
the take-off platform. The critical point (K) in the model of jumping hill is 160 cm. The dolls are able to jump on this model hill. The position
of start on in-run is 150 cm away from the edge of platform. The peg, which releases the strength of the jump doll, was put on six places
every 4 cm away from the edge of platform. Five times trials in two jump dolls were executed for every peg point. All the jump actions
were recorded by the NAC video camera with 500 fps.
Results: The elapsed time for jump actions from squat position to full extension and speed of take-off were almost the same in both types.
Using the same release point, the maximum flight distance was occurred in each doll. The release point is 4 cm before the edge of
platform. The flight distance is 125 cm in type 1, and 166 cm in type 2. On the other hand, the minimum flight distance was observed in
initiating jump action at the 12 cm before the edge. The flight distance is 88 cm in type 1, and 128 cm in type 2.
Discussion: Smooth action on each joint is achieved by a bearing devices, although the doll is made by wood, The doll-model produces
the same strength at take-off actions, because, it is possible to take the same squat position anytime. Therefore, the jump -doll can be
used in the experiment of ski-jump. In this study, the difference in the flight distance is only attributed by the difference of the timing of the
jump action. As an evidence of the transition of the power, the oscillation of skis was exactly observed during the initial flight phase. This
phenomenon already pointed out even in the human action (Sasaki et al., 2005). In the flight distance, the most effective timing for beginning
the action is clarified in this experiment by the jump-doll.
Conclusion: Until the 4 cm from the edge of platform, the later the timing of beginning the action is, the larger the flight distance is. The
jump-doll always transmits almost same power.
OPTIMIZATION OF AERODYNAMIC STABILITY IN SKI JUMPING: THE TUG-OF-WAR BETWEEN SAFETY AND PERFORM-
ANCE
MARQUES-BRUNA, P., GRIMSHAW, P.
EDGE HILL UNIVERSITY
Introduction: Past research in ski jumping has aimed to increase jump length and modify ski length and hill design to make the sport
safer (Schwameder, 2008). However, the assessment of aerodynamic stability (Anderson, 2007) for improved safety has received less
attention (Seo et al., 2004). Thus, this study aimed to model aerodynamic efficiency and stability in pitch in ski jumping as a function of
athlete’s posture. The findings may be used to optimise flight posture and warrant safer training and competition.
Methods: Mathematical modelling was carried out using a hypothetical ski jumper with a typical mass of 70 kg, height of 1.76 m and ski
length of 2.57 m (Seo et al., 2004). Lift (FL), drag (FD), lift/drag ratio (FL/FD), dPitching-moment/dAngle-of-attack slope (dM/dAA) at the trim
AA and oscillatory frequency (FREQ) (Anderson, 2007) were calculated as a function of AA, ski opening angle (SOA; at 20°, 25° and 30°)
and forward-leaning angle (FLA; at 0°, 10°, 20°, 30° and 40°) (Seo et al., 2004). Air density was set at 1.18 kg/m3, and air speed at 25 m/s
to simulate competition at a large jumping hill (Schwameder, 2008).
Results: FL was largest with SOA = 30° & FLA = 0°-10°. FD increased monotonically from AA = 10°. FL/FD peaked at AA = 2°-12°, at which
FL was rather low. dM/dAA became steeper with increased SOA and FLA, ranging from – 0.82 Nm/° for SOA = 20° & FLA = 0° to – 2.67
Nm/° for SOA = 30° & FLA = 40°. FREQ increased as a function of SOA and FLA, showing about half a cycle per second (0.51 Hz) for SOA =
30° & FLA = 10°.
Discussion/Conclusion
An optimised flight posture of SOA = 30° & FLA = 10° is suggested. This is a high-lift configuration that yields steep dM/dAA and high
oscillatory frequency upon sudden deviations from trimmed flight. The high frequency may initiate transitory dynamic oscillations (Anderson,
2007). The findings add to the current priority to warrant safety in the sport (Schwameder, 2008).
References
Anderson, J.D. (2007). Fundamentals of aerodynamics. (4th ed.). McGraw-Hill. London.
Schwameder, H. (2008). Biomechanics research in ski jumping, 1991-2006. Sports Biomechanics. 7 (1): 114-136.
Seo, K., Watanabe, I. and Murakami, M. (2004). Aerodynamic force data for a V-style ski jumping flight. Sports Engineering. 7: 31-39.
PHYSIOLOGIC RESPONSES OF LOW AND HIGH STRESS RESPONDING RECREATIONAL ALPINE SKIERS TO DIFFERENT
SKIING PACES
SEIFERT, J., SCHEIBER, P., MÜLLER, E.
MONTANA STATE UNIVERSITY, BOZEMAN, MONTANA; UNIVERSITY OF SALZBURG, SALZBURG, AUSTRIA
Introduction: Previous studies have demonstrated that there are skiers who demonstrate a low physiological response (LO; low lactate
and HR), while others have a high physiological response (HI; high lactate and HR) when skiing at similar velocities. However, it is unknown
how LO and HI respond to different skiing paces when compared to their individual self-paced skiing. It is important to understand
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