INTRODUCTION: Strong vibrations are excited at the ski-snow interface (Mester et al., 1999). These equipment vibrations may have an ill effect on motion control (steering quality) and the risk of falls. In this study, time/frequency aspects of equipment vibrations were studied using wavelet analysis. The purpose was to quantify amplitudes and frequencies in short turns, carving turns, and gliding in tuck position at different snow conditions. METHOD: Ten experienced skiers performed 24 runs in which they performed a jump in stance, 5-7 short turns, 6 carving turns, followed by gliding in tuck position until the final stop turn. The skiers were equipped with 1-D acceleration sensors (Analog Devices™ (ADXL series), range: 120g) placed in axial direction (parallel to the tibia) on the shaft of the ski boot, above the heel. The acceleration Signal was recorded with a mobile EMG measurement device (Biovision™) carried in a backpack. Measurement frequency was 2000 Hz. The recorded acceleration signal was resolved with a wavelet transformation into intensities calculated for a set of 22 center frequencies between 0.6 and 80 Hz. RESULTS and DISCUSSION: Peak accelerations (20-30g) were found in the steering phase in short turns. Vibrations are small in turn initiation (~2g) and during gliding (~5g). In carving Vibration amplitudes are in the range 10-15g. It seems that Vibration amplitudes are high when the ski skids and when the ground reaction forces are high. Frequency spectra are highly subject specific and not equipment specific, although subjects used the same test skis. In all subjects the peak intensities were found in the range 5-30Hz. As the snow turned softer in the course of the day frequencies above 15-20Hz disappeared.
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