SIMULATION OF VIBRATIONS IN ALPINE SKIING

Abstract

Introduction: Simulation of movements has become a significant method in biomechanical research. Especially in alpine ski racing, which is characterized by a great variety of situations, this method is of crucial importance. The main component in alpine skiing technique is the control of vertical load distribution. A few studies have showed that this coordinating capability is considerably influenced by physical conditions. On the one hand, the physical load is related to high external forces, on the other hand, it is the result of oscillating ground reaction forces. The lack of knowledge of how to control vibrations in alpine skiing was the reason for this study. Because of the difficulties in analyzing neurophysiological parameters on the ski slopes, we have developed a simulation system to obtain more information about the control of vibrations in alpine skiing. Methods: To generate vibrations we used a roller ski system with eccentric rolls driven by a treadmill. In view of the results of field studies and theoretical considerations, we worked with a vibration frequency between 4 and 20 Hz and an amplitude between 4 and 21 mm. One group of persons involved in the study were ski teachers from the ‘German Ski Teachers’ Federation’, the other group were recreational skiers. The subjects were subjected to vibrations for about 20 sec. in an upright stance and for the same time in a crouching stance. To measure the generated vibrations and their influence on body movements we used a one dimensional acceleration sensor attached to the middle of the central axis of the ski (sampling frequency 500 Hz), a goniometer (attached to the right knee) and a video system. To assess the vibration control abilities of the subjects we used the parameters ‘resultant acceleration’ and ’amplitude of knee angle’. Results and Discussion: Depending on the used frequency and amplitude the maximum acceleration reached +50/-40 g, the average maximum acceleration in the course of 15 sec. reached +40/-30 g. The data for acceleration measurements on the slope proved to be similar. The statistical data analysis showed significant intra-individual (upright stance/crouching stance) and inter-individual (ski teacher/ recreational skier) differences in resultant acceleration and amplitude of knee angle. The differences depend on the characteristics of the vibration. Conclusion: At this point in our research, we believe that there is an individual optimum of vibration control in regard to frequency and amplitude, depending on anthromethric measurements and physical conditions. These aspects are being researched in a current study.