Die Evidenz des Dehnungs-Verkürzungszyklus im Skilanglauf
|Project manager:||Lindinger, Stefan (Universität Salzburg / IFFB für Sport- und Bewegungswissenschaft / USI Christian Doppler Laborytory "Biomechanics in Skiing", Tel.: +43 (0) 662 8044-4886, stefan.lindinger at sbg.ac.at); Müller, Erich (Universität Salzburg / IFFB für Sport- und Bewegungswissenschaft / USI Christian Doppler Laborytory "Biomechanics in Skiing", Tel.: +43 (0) 662 8044-4886, erich.mueller at sbg.ac.at)|
|Project staff members:||Rapp, Walter; Gollhofer, Albert|
|Research institution:||Universität Salzburg / IFFB für Sport- und Bewegungswissenschaft / USI Christian Doppler Laborytory "Biomechanics in Skiing"|
|Format:||Project (Database SPOFOR)|
|Project duration:||04/1990 - 02/2000|
Grundsätzlich die Beantwortung der Frage: Kommen Dehnungs-Verkürzungs-Reflexe im Skilanglauf überhaupt vor? Ab welchen Geschwindigkeiten treten sie auf? Welche Muskelgruppen sind hauptsächlich betroffen? Welche Konsequenzen für das Krafttraining können gezogen werden?
In cross country skiing complimentary to the classical diagonal technique a vast variety of different styles have been developed in the last decade. Emphasis is given to two aspects: Which type of technique enhances the runners performance capability and which type of technique enhances the running economy? Both orientations have been treated experimentally. Specific interest was given to the question, which type of technique benefits to what extent from muscular actions characterised by the stretch-shortening-cycle (SSC). From running (Komi 1987) and jumping (Gollhofer 1995) it has been shown that SSC behaviour is highly effective both in terms of performance potentiation as well as in terms of efficiency (Bosco et al. 1982). The purpose of this study was to investigate the muscular pattern of leg and trunk muscles in order to verify differences in muscular involvement in a series of techniques in cross country skiing.
In CDT the comparison between WAX and NOWAX conditions revealed differences in the ground reaction forces and in TA activation. Whereas in WAX condition the force loading during contact is characterised by a two phased pattern, in NOWAX only one loading phase can be observed. The differences in force regulation are also reflected in the TA muscle activation pattern (fig. 1). All other muscles however did not vary substantially between both CDT modalities! In CDT the characteristic quick bouncing could be observed in the ground reaction forces. Detailed analysis revealed that 40ms following dorsiflexion in the ankle joint segmented EMG activation could be seen both in GAS as well as in PER muscles. The marked differences in force and TA activation may be reflected by changes in the strategy of the runner. In WAX condition an optimisation is performed by a long loading phase, controlled by the plantar flexor TA in order to achieve a quick bouncing effect in the push-off phase. Both, time characteristics as well as EMG pattern of lower limb muscles demonstrate high reflex activation. This pattern is closely related to muscular actions seen in stretch-shortening cycle. In NOWAX-condition, TA is deactivated at the early instant of stance, leading to a smooth rise in ground reaction force. Starting from a distinct force niveau a quick bouncing is performed. In conclusion, in accordance to previous studies it may be assumed that SSC is the natural action profile of the lower limb muscles under controlled (WAX) conditions. In less controlled situations (NOWAX) the neuromuscular system switches from a reactive type pattern to an orientation type (stabilisation type pattern).