INTRODUCTION: The movement of the center of mass (COM) in cross-country skiing (XCS) has been described by several authors (e.g. Norman & Komi, 1987); however, only at moderate skiing speeds and no relation to performance was analyzed. In sprint running low vertical oscillation of the COM was shown to be beneficial (Anderson, 1996). Whether or not Variation of the COM in horizontal and vertical direction in XCS is related to maximal speed (Vmax) is still open to question. METHOD: 16 elite XC skiers performed Vmax tests roller skiing on a treadmill using double poling (DP) (1.5°), and diagonal stride (DIA) (7°). A continuous protocol with increases in treadmill speed every 10 s was used. Whole body 3D motion was captured using VICON MX. COM was calculated by a modified Plug-ln Gait model. Five cycles were analyzed and time normalized at the speed increment that all skiers were able to finish (DP 30 km/h, DIA 18 km/h). Minima, maxima and range of motion for all three coordinates, Potential energy (Epot), and maximal kinetic energy (Ekin) were calculated. Variables were correlated to the respective Vmax by using a Pearson Product Moment correlation. Significance level: a<0.05. RESULTS: For DIA the fastest skiers demonstrated larger vertical COM oscillation (abs. r=.71 P<.01; %body height: r=.74 P<.001), with greater lowering after pole plant (r=.62, P<.05), higher maximal upward (r=.55, P<.05) and downward (r=.69, P<.01) velocities, with higher changes in Epot (r=.70, P<.01), higher maximal Ekin in downward and upward motion (r=.69, P<.01, r=.5, P<.05) and less displacement in anterior-posterior direction (r=-.5, P=.05). During poling phase in DP the faster skiers moved their COM more in a forward direction (r=.77, P<.001) with greater lowering (abs: r=.53, %BH r=.58, P<.05) but no difference in the vertical rise (r=-.21, P>.05). In Swing phase they demonstrated less backward movement (r=-.68, P<.01). No relation to Vmax of total back-forth motion (r=-.42, P>.05) and range of vertical motion (r=.33, P>.05) was found. Faster skiers had higher maximal forward and downward velocity during the poling phase (r=.6, P<.01, r=.69, P<.01) and lower backward and upward velocity during the swing phase (r=-.65, P<.01, r=-.72, P<.001). Epot, was not related (r=.37, P>.05), whereas downward and upward Ekin were respectively, positively and negatively related to Vmax (r=.71, r=-.75, P<.001). DISCUSSION& CONCLUSION: The course of the COM for fast skiers demonstrated inverse patterns for DP and DIA. For DIA the faster skiers demonstrated greater vertical oscillation with higher velocities but less change in horizontal direction, whereas in DP the opposite was found. Hence for DIA large amplitude in a vertical direction seems to be the prerequisite for production of optimal leg forces, placement of poles and skis for push-off and to optimize gliding. This pattern is in contrast to comparable types of locomotion like running or walking, where greater changes of COM in vertical direction are associated with increased energy demand and decreased performance. Large upward raise of the COM at high velocities is disadvantageous for DP. Emphasize should be placed on downward and forward motions during the poling phase with less displacement back- and upward during swing phase. This technique pattern might be related to higher impulses of forces, longer swing times with lower cycle rates and different body motion during XCS.
© Copyright 2010 Book of Abstracts. 5th International Congress on Science and Skiing, Dec. 14 - 19, 2010, St. Christoph am Arlberg. Veröffentlicht von University of Salzburg, Interfakultärer Fachbereich Sport- und Bewegungswissenschaft/USI. Alle Rechte vorbehalten.