INTRODUCTION: Today's cross-country (XC) ski racing is determined by high speeds, reached by higher upper and lower body capacity and by further developed techniques. In contrast to double poling (DP), kick DP (DPK), is less focused and used, especially in sprint skiing. Due to more demanding tracks in classic skiing, the importance of DPK for race performance will grow, especially in high speed events. Compared to DP (Holmberg et al., 2005), DPK is much less investigated and there is little knowledge on speed control strategies in DPK (Nilsson, 2004). Thus the aim of the study was to identify cycle and force adaptations to different submaximal DPK speeds. METHOD: Ten elite XC skiers performed DPK at 13, 16 and 19 km.h-1 at a treadmill inclination of 3°. Joint angles (goniometers), pole (strain gauge; all 2000 Hz) and plantar force (Pedar Mobile; 100 Hz) were recorded and cycle characteristics were calculated from these data. Repeated-measures ANOVA, including Bonferroni alpha correction, was calculated for speed differences. Pearson's product-moment correlation was used for pairwise comparison of changes (13 —> 19 km.h-1) in cycle, poling and push-off characteristics. Statistical level of significance was set at P<0.05. RESULTS: One DPK cycle (19 km.h-1) consists of two poling phases (2 x 15% cycle time), each followed by a gliding phase (2 x 14% CT), preceding right or left leg push-off (10% CT). Leg push-off goes along with an unloading phase on the contralateral side. The following distinct leg swing accompanies a one-legged gliding phase (11% CT). Cycle length (CL) and cycle rate (CR) gradually increased from 13 to 19 km.h-1 (10.9 -»13.6 m; 0.33 -» 0.39 Hz; all P<0.01), corresponding changes of 20 ± 4% (range: 14 -28%) and 15 ± 5% (6 - 20%). Absolute and relative (% CT) poling time (PT) decreased across speeds (P<0.01) (min. 0.39 ± 0.02 s). Peak/average pole forces (PPF; APF) and rate of force development (RFD) increased with speed (all P<0.05) reaching a PPF maximum of 29 ± 6% body weight (BW). Change in CL (13-> 19 km-h "1) was correlated to change in APF (r=0.71; P<0.05) and relative PT (r=-0.88; P<0.01). Absolute leg push-off time decreased across speeds (min. 0.26 ± 0.07 s) and relative (% CT) leg push-off time was shorter at 16 vs. 13 km.h-1. Peak plantar force was higher at 19 (max. 190 ± 25% BW) vs. 13/16 km.h-1 and average force was higher at 19/16 (max. 123 ± 5% BW; P<0.05) vs.13 km.h-1, with no changes in RFD. No correlations of CL changes to leg force changes and push-off time changes were found. DISCUSSION & CONCLUSION: The findings of the present study suggest that higher DPK speeds require the production of higher forces in a shorter time and at higher frequencies. Adaptation of CL is thereby mainly determined by changes in poling. Athletes have to focus on a modern poling action in DPK during specific technique, endurance and strength training.
© Copyright 2012 Science and Skiing V. 5th International Congress on Science and Skiing, Dec. 14 - 19, 2010, St. Christoph am Arlberg. Published by Meyer & Meyer Sport (UK) Ltd.. All rights reserved.