Performing a forward dive with 5.5 somersaults in platform diving: simulation of different technique variations.

Performing dives with multiple somersaults is an inherent component of competitive diving. In individual international competitions, dives are performed from a 1- or 3-m springboard as well as from a 10-m platform, and divers use different technique variations in accelerating and decelerating rotation about the somersault axis. Therefore, the first aim of this study was to evaluate the effect of different technique variations in accelerating and decelerating rotation about the somersault axis in a 109C dive (4.5 forward somersault in a tucked posture) by means of a multi-body computer simulation model based on the real performance of an expert diver. The second aim was to evaluate the feasibility of adding an additional somersault rotation to the 109C dive. The results revealed that different technique variations accounted for different amounts of gain and loss in somersault rotation, whereas no isolated technique variation accounted for an additional somersault rotation. Applying an optimized technique variation together with an increase in angular and linear momentum allowed the simulation model to perform a forward dive with 5.5 somersaults under achievable biomechanical constraints (1011C dive). It is concluded that the 1011C would be a feasible skill for a diver whose sensory-motor system is adequately adapted to withstand angular velocities of approximately 1200°/s and who is able to perform a double tucked somersault in a split-tuck posture above the platform level. Implications for changes in training practices and platform equipment are discussed.

Downhill turn techniques and associated physical characteristics in cross-country skiers.

Three dominant techniques are used for downhill turning in cross-country skiing. In this study, kinematic, kinetic, and temporal characteristics of these techniques are described and related to skier strength and power. Twelve elite female cross-country skiers performed six consecutive turns of standardized geometry while being monitored by a Global Navigation Satellite System. Overall time was used as an indicator of performance. Skiing and turning parameters were determined from skier trajectories; the proportional use of each technique was determined from video analysis. Leg strength and power were determined by isometric squats and countermovement jumps on a force plate. Snow plowing, parallel skidding, and step turning were utilized for all turns. Faster skiers employed less snow plowing and more step turning, more rapid deceleration and earlier initiation of step turning at higher speed (r = 0.80-0.93; all P < 0.01). Better performance was significantly correlated to higher mean speed and shorter trajectory (r = 0.99/0.65; both P < 0.05) and to countermovement jump characteristics of peak force, time to peak force, and rate of force development (r = -0.71/0.78/-0.83; all P < 0.05). In conclusion, faster skiers used step turning to a greater extent and exhibited higher maximal leg power, which enabled them to combine high speeds with shorter trajectories during turns.

Aerodynamic drag is not the major determinant of performance during giant slalom skiing at the elite level.

This investigation was designed to (a) develop an individualized mechanical model for measuring aerodynamic drag (F(d) ) while ski racing through multiple gates, (b) estimate energy dissipation (E(d) ) caused by F(d) and compare this to the total energy loss (E(t) ), and (c) investigate the relative contribution of E(d) /E(t) to performance during giant slalom skiing (GS). Nine elite skiers were monitored in different positions and with different wind velocities in a wind tunnel, as well as during GS and straight downhill skiing employing a Global Navigation Satellite System. On the basis of the wind tunnel measurements, a linear regression model of drag coefficient multiplied by cross-sectional area as a function of shoulder height was established for each skier (r > 0.94, all P < 0.001). Skiing velocity, F(d) , E(t) , and E(d) per GS turn were 15-21 m/s, 20-60 N, -11 to -5 kJ, and -2.3 to -0.5 kJ, respectively. E(d) /E(t) ranged from ∼5% to 28% and the relationship between E(t) /v(in) and E(d) was r = -0.12 (all NS). In conclusion, (a) F(d) during alpine skiing was calculated by mechanical modeling, (b) E(d) made a relatively small contribution to E(t) , and (c) higher relative E(d) was correlated to better performance in elite GS skiers, suggesting that reducing ski-snow friction can improve this performance.

Mechanical parameters as predictors of performance in alpine World Cup slalom racing.

The aims of the present study were to develop a method for classifying slalom skiing performance and to examine differences in mechanical parameters. Eighteen elite skiers were recorded with three-dimensional kinematical measurements and thereafter divided into a higher (HP) and lower performance group, using the ratio between the difference in mechanical energy divided by the mass of the skier and section entrance velocity (Δe(mech)/v(in)). Moreover, the skiers' velocity (v), acceleration (a), center of mass turn radii (R(CM)) and skis' turn radii (R(AMS)), ground reaction forces (GRF) and differential specific mechanical energy [diff(e(mech))] were calculated. v and diff(e(mech)) were different between the performance groups (P<0.001 and <0.05), while no inter-group differences in R(CM), R(AMS), a and GRF were observed. A relationship between R(AMS) and diff(e(mech)) was demonstrated (r=0.58; P<0.001). The highest GRFs were related to the lowest diff(e(mech)) and a was related to GRF (r=-0.60; P<0.001). The Δe(mech)/v(in) predicted the performance over short course sections. The HP skiers skied with a higher v and a similar range of diff(e(mech)). We suggest that shortest R(AMS) and the highest GRFs should be reduced in elite slalom in order to increase performance.