INTRODUCTION: Vibrations acting on the skier are the result of the ski-snow interaction or of equipment resonances. Vibrations of the ski boot (Federolf et ai., 2007) initiate vibrations of soft tissue compartments of the skiers body. In this study, vibrations of soft tissue compartments of the leg in three different skiing situations and corresponding responses in muscle activation were quantified. METHOD: Ten experienced skiers performed 24 runs, which included short turns, carving turns and straight gliding. Vibrations of the ski boot were determined as described earlier (Federolf et al., 2007). Vibrations of soft tissue compartments were quantified with acceleration sensors (range 35g) mounted on the triceps surae, quadriceps and hamstrings. Muscle activation was measured using bipolar surface EMG sensors on the gastrocnemius, vastus medialis, vastus lateralis, and m. semitendinosus. The Vibration signal was resolved using a set of 22 wavelets with center frequencies between 0.6 and 80 Hz. EMG data was resolved using 13 wavelets with center frequencies between 6.9 and 542 Hz. Mean frequency spectra were determined by averaging over 4 turns (short turns, carving) or by averaging over 2 seconds (gliding). Resonance spectra of soft tissue compartments were determined by dividing the mean acceleration intensity in each frequency band by the mean ski boot Vibration intensity in the same frequency band. RESULTS and DISCUSSION: Frequency and amplitudes of muscle compartment vibrations depend on the input signal (ski boot vibrations) and on the resonance properties of the soft tissue compartment. The shape of the resonance curves and the resonance frequencies are muscle and subject specific and are determined by the skiing style, e.g. from carving turns to gliding (Figure 1). Changes due to different ski or snow conditions were small and in the same range as the fluctuations observed between different runs.
© Copyright 2007 4th International Congress on Science and Skiing. Veröffentlicht von University of Salzburg. Alle Rechte vorbehalten.