Kinematic, Kinetics and Neuromuscular Comparative

Kinematic, kinetics and neuromuscular comparative analysis of the “turn movement” between alpine skiing and a new ski simulator POZZO Renzo1 , Consuelo Pasutto1, Casasola Stiven1, Grazzina Francesco1, Rejc Enrico1, Cotelli Chicco2,Canclini Arrigo2, 1Institute of Sport Science, University of Udine, Italy 2 FISI-LAP S.Caterina Valfurva Italy Introduction To date, a number of simulators ranging from portable equipment to artificial inclines, have been studied. Their efforts were aimed at analysing the effectiveness of existing simulators and to determine the prerequisites necessary to achieve suitable simulators such as Gleitroll bret, Ski power simulator, Ski power home-trainer, the Slide, Pro-Fitter and Skier’s Edge. The aim of this study is to verify the affinity of the “curve movement” structure carried out in a real giant slalom (GS) and on a “new generation” simulator (SS). The simulator used has two breech footboards which can rotate around their longitudinal axis and can be made to vibrate with a frequency variable between 0 to 50 Hz. The athlete is tied with a particularly waist belt from which a cable, which passes through a return pulley, is connected to a traction lever which allows for the dynamic situation found on the ski slopes to be reproduced. Methods Three different methods have been used: kinematic three-dimensional analysis, analysis of reacting forces at ground level and electromyography (EMG). In the first case, two Canon Movie XM2 videocameras with acquisition frequency of 50 Hz and dedicated software SIMI Motion were used. The two cameras were positioned at 90 degrees with respect to each other and used simultaneously to record the movements. The data were then processed by computer. Calculations of the principal kinematic parameters, segment movements, angles and angular speed were carried out. To analyse the reaction forces at ground level, SAIR-technology soles with hydro cell sensors having an acquisition frequency of 100 Hz were used. EMG acquisition was made by an electromyographer MEGA with 8 channels and a sample rate of 1000 Hz. Results Kinematics parameters reveal some differences on the time history of the knee and ankle joints between the GS and SS. On the SS the joint variations show the same time phase for both legs, whereas in the GS the curves are in a shifted phase. This is due by the difference external constrains affecting the flexion phase. In GS the ski move laterally from each other and this causes the external leg to be much more extended then the internal leg . In SS the feet are fixed to the plates and can only rotate (tilting) according to the frontal plane of the skier. Maximal knee flexion are consistent in the vibration exercise and reach a mean value of 110 deg and 85 deg for external and internal knee, whereas in SS the value are 96 deg and 60 deg respectively. Referring to the distribution of the internal and external reaction forces, the pattern of the curve are in agreement for both situations GS and SS. Mean values of peak force during GS under different vibratory condition and on the SS revealed following: highest value, 2500 N external and 1300 N internal, occurred during the 30 Hz vibration, while in the GS they reach 1400 N and 500 N respectively. In the GS the force curves decrease to a minimum corresponding to the unloading phase between the each turn. Quantità di attività muscolare (IEMG) In SS situation, on the contrary, the minimum is iEMG observed every two maximal flexion, i.e. only 450 when the leg changes his function from 400 350 external to internal. This is because under the GM_DX 300 BF-DX SS there are no centripetal forces allowing the GAS-DX subject to regain his vertical position without 250 TA-DX VM-DX great effort, so the leg should still act again the 200 RF-DX [microVolt*s] VM-SN ground to maintain the dynamic equilibrium. 150 RF-SN The EMG parameters, activation time, RMS 100 amplitude and IEMG integral, showed a high 50 similarity between the two experimental 0 conditions. For the biceps femoris, vastus no Hz 30Hz 40Hz 50Hz slalom medialis, and rectus femoris there is a linear tendency to increase the RMS values Fig. 1 Average values of RMS amplitude for the leg muscles according to the augmented frequency of vibration. During the slalom the muscles show theirs maximum RMS values. Analogues considerations are founded for IEMG parameter. Discussion/Conclusion by means of this study it is confirmed how the concept of specificity of exercise conditions can be evaluated. The similarity of kinematic, kinetic and neuromuscular structure of the movement are established between the slalom and simulator conditions. According to these results it is possible to make new assumption in order to improve the constrains of the simulator (centripetal force) and make it more useful for training of high level skiers.. References Frick,U., et al (1997).Types of muscle action of leg and hip extensor muscles in slalom In: Science and Skiing 262- 271 . .

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