INTRODUCTION: Kick double poling (DPK) is considered a highly demanding classic skiing technique (uphill; 2-4°). The complex coordination of alternating pole and leg push-offs, swing and gliding phases highly demands the skiers' coordinative skills. Compared to DP or DIAG, DPK is less practiced in training and racing, especially in sprint, showing high potential in more efficient use and improvement of this skill. In contrast to DP and DIAG (i.e. Lindinger et al. 2009a/b; Stöggl et al. 2009), there is coaches' experience but little evidence about factors determining the quality of DPK, thus this pilot study aimed to compare biomechanical characteristics among different skill levels. METHODS: Jen elite XC skiers performed DPK at 19 km.h-1 on a treadmill (3° inclination). Pole (2000 Hz) and plantar forces (Novel; 100 Hz) and joint angles (2000 Hz) were recorded. Skiers were grouped into two different DPK skill level groups (A [best five] and B) by 'expert rating' methods (video evaluation) (Holmberg et al. 2005). All data were checked for normality. For group differences Mann-Whitney U tests were applied (PO.01** and P<0.05*). RESULTS: Group A (rated as technically better) showed 15% longer cycle length (CL) (14.7 ± 0.9 vs. 12.5 ± 0.6 m) and 17% lower cycle rate (CR) (both PO.01) (no differences in body height). Arm/leg cycle characteristics (A vs. B): Absolute poling time (s) was similar and recovery time 21% longer (1.00 ± 0.10 vs. 0.79 ± 0.05 s; PO.01) with a 7% longer relative (% cycle time (CT)) recovery time (72 ± 0.03 vs. 67 ± 0.02 %CT) (shorter poling) (both PO.05) shown in the "better" skiers. Showing no differences in relative (%CT) leg ground contact time (GCT) or RT, absolute GCT and RT were 14 & 17% longer in group A vs. B (GCT: 2.36 ± 0.21 vs. 2.01 ± 0.11 s; RT: 0.42 ± 0.06 vs. 0.35 ± 0.02 s), due to 15% longer CT (all PO.05). Pole/leg forces: Pole forces did not show any group differences. Group A generated 17% higher peak total (208 ± 11 vs. 175 ± 23 %BW) and forefoot leg forces. Due to both, the higher peak forces and 30% longer push-off times (0.31 + 0.07 vs. 0.22 ± 0.04 s; PO.05), group A skiers generated 33% greater Impulses of force (38.5 ± 9.7 vs. 25.8 ± 3.4 %BW-s) during push-off. Gliding/swing: Single leg gliding time (=positioning for double poling action/leg joint extension) and leg swing time (synchronized with pole push-off) were 21 and 33% longer in group A (all PO.05). Joint angles: Elbow angle minimum during pole thrust and angle at pole-out were smaller in group A, whereas elbow flexion and extension ranges of motion as well as angular velocities (flex & ext) were greater (all P<0.05). Knee and hip flexion as well as knee extension ranges of motion (push-off) were greater in group A. DISCUSSION/CONCLUSION: The higher CL/lower CR basically characterizes the higher technique level, confirming earlier results for DIAG (Lindinger et al. 2009b). As key factor the better leg force production seems to differentiate between DPK skill levels. These results may serve as base for technique training and contribute to classic skiing performance.
© 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.