INTRODUCTION: With the development of skiing disciplines professional alpine skiing has reached the degree, where top results are very hard to reach. In the process of training there is a mosaic of special elements for each discipline in alpine skiing. The purpose of our work was to investigate on different adaptations of skeletal muscles vastus lateralis (VL) and vastus medialis (VM) contractile properties between two groups of world cup racers: giant slalom and slalom racers (GS&SR) vs. super G and downhill racers (SG&DR). METHOD: Fourteen top world cup racers in alpine skiing (age 27 ± 3 years; height 183 ± 5 cm; weight 87 ± 7 kg) were included in the whole research. Contractile properties were measured using Tensiomiographic method (TMG). TMG assesses mechanical twitch response after single electrical impulse stimulation and from the twitch response we extracted maximal amplitude (Dm), delay time (Td) between electrical impulse and 10% of Dm, contraction time (Tc) from 10% to 90% of Dm, and half relaxation time (Tr) from 90% to 50% of Dm. The differences between GS&SR and SG&DR were tested with T-test for independent samples and statistical significance was confirmed at P < 0.05. RESULTS: For VM we found lower Dm in GS&DR for 19% (P = 0.04), however, we found shorter Tc and Tr in GS&SR for 8% (P = 0.04) and 44% (P = 0.03), respectively. Apart of measurements at 30 degrees of knee flexion we compared Tc also knee angles from 0 to 60 degrees. SG&DR have consistently shorter Tc in VM at knee angles from 20 to 60 degrees (P < 0.05). In the contract, GS&SR have shorter Tc in VL at knee angles from 0 to 10 degrees of knee flexion (P < 0.05). DISCUSSION: In our previous studies we demonstrated that Tc measured by TMG correlates significantly with fibre type distribution (Dahmane et al., 2000), being lower in muscles with lower proportion of type-l fibers and we demonstrated also Dm being lower in muscles with higher muscle tone (Pisot et al., 2008). From the results of this research we could conclude that there are adaptive differences in two skeletal muscles between disciplines in alpine skiing. Differences can be explained by the biomechanical differences in skiing technique typical for each discipline. Based on the cross-bridge theory it was expected that contractile properties of skeletal muscle change with knee angle. However, we have proofed that this change could be further influenced by human sport involvement. It is well established that specifics of sport training could alter skeletal muscle geometry and architecture as well. In alpine skiers we have to consider this carefully as both vastii muscles act synergistically on knee joint. Therefore, asymmetry of VM and VL contractile properties has to be monitored and studied for optimal performance and also for knee clinical health.
© Copyright 2012 Science and Skiing V. 5th International Congress on Science and Skiing, Dec. 14 - 19, 2010, St. Christoph am Arlberg. Veröffentlicht von Meyer & Meyer Sport (UK) Ltd.. Alle Rechte vorbehalten.