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Cross-Country Skiing

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Cross-Country Skiing Nytt fra idrettsforskingen: Rapport fra “European College of Sport Science” Norges Idrettshøyskole arrangerte i år den store forskingskonferansen “European College of Sport Science”. Vi har fått tillatelse av arrangøren å presentere en del foredrag (abstract) som er av interesse for langrennstrenere. Vi har delt presentasjonene i to: 1) abstract som omhandler langrenn og 2) abstract som omhandler utholdenhetstrening rettet mot elite utøvere. Abstracts er på engelsk, og viktige referanser er vedlagt nederst på hvert enkelt abstract. God lesning! CROSS-COUNTRY SKIING: PREDICTION OF CROSS-COUNTRY SKI SEASON PERFORMANCE BASED ON A LINEAR REGRESSION MODEL OF LABORATORY ROLLER SKI CAPACITY AND VO2MAX TEST Naef, N., Steiner, T., Müller, B., Wehrlin, J.P. Institution: Swiss Federal Institute of Sports, Magglingen, Switzerland Introduction: Cross-country (XC) ski-specific testing is used to support elite athletes regarding their training control as well as to predict performance of competitive ski season (Alsobrook & Heil, 2009, Staib et al., 2000). The purpose of this study was to investigate the relationship between the results of two different laboratory preseason roller ski tests and the XC ski performance of the following season as well as its predictability with a linear regression model. Methods In October 2008, 14 male XC skiers of the Swiss National U20 (n=5), U23 (n=2) and Elite (n=7) Distance Ski Team completed two laboratory roller ski tests on a large motor-driven treadmill. Athletes performed a maximal diagonal stride test to measure VO2max. 24 hours later they carried out a maximal double poling capacity test with self selected speed during three stages of eight minutes (5 min at 3° inclination and 3 min at 5° inclination) to establish maximal possible distance. XC ski season performance was ranked by the 4th XC ski distance International Ski Federation (FIS) points list 2008/2009. Spearmen correlation analyses and multiple linear regression models were applied. Results Athletes achieved a mean total distance of 5299.3 ± 460.5m, a VO2max of 77.4 ± 4.6 ml/min/kg and mean FIS Points of 59.7 ± 44.1 (range = 1.2 - 130.5). There was a negative correlation between distance and FIS points as well as VO2max and FIS points (r = - 0.832; p < 0.001 and r = - 0.510; p = 0.062, respectively). Age was significantly correlated to FIS points (r2 = - 0.638; p = 0.014). The best linear regression model to predict FIS points was: FIS points = - 0.069 * distance [m] - 2.897 * VO2max [ml/min/kg] + 650.95 with a mean residual of 15.6 ± 9.2 points. Correlation between XC ski performance and the linear regression model was significantly (r2 = 0.790, p < 0.001). Discussion and Conclusion These findings suggest that distance achieved during the capacity test and VO2max are important determinants of the following XC ski season performance. Our linear regression model based on a ski-specific laboratory test is highly correlated with seasonal performance (FIS). We suggest that this model is a useful tool to predict XC ski performance of the following winter season, in spite of the long time frame and possible confounding factors (health problems, ski preparation, race tactic, etc). References Alsobrook NG, Heil DP (2009). Eur J Appl Physiol, 105, 633- 941. FIS point rules: http://www.fis-ski.com/data/document/pktrl0809e.pdf Staib JL, Im J, Caldwell J, Rundell KW (2000). J Strength Cond Res, 14(3), 282-288. The relationship between oxygen extraction in the arms and legs to force and exercise intensity in diagonal skiing Björklund, G., Stöggl, T., Carlsson, L., Dovrén, L., Holmberg, H.C. Institution: Mid-Sweden University Department: Swedish Winter Sports Research Centre, Department of Health Sciences Introduction: Diagonal skiing (DIA) is the main classical cross-country technique used when skiing uphill. Two interesting findings when examining this technique at submaximal workloads have been that 1) O2 extraction was lower in the arms than the legs (Calbet et al., 2005) and 2) lactate oxidation mainly occurred in the leg muscles simultaneously with a high lactate production in the arms (Van Hall et al., 2003). At present no data have described how these findings may be associated with force generation and the muscle activity measured by electromyography (EMG). Thus, the aims of this study were to examine i) the interaction between physiological and biomechanical variables and ii) the effect of changes in submaximal exercise intensities in diagonal skiing. Methods: Eleven elite XC skiers (age 22±3yr; VO2max 69±3 mL/kg/min, obtained during DIA on a treadmill) performed a protocol of 3 min at 90% followed by 6 min at 70% of VO2max DIA. Cardiorespiratory data were collected continuously, along with determination of blood gases and metabolites from a. femoralis, v. femoralis and v. subclavia. Pole and foot forces (Pedar, Mobile 100Hz) and EMG data from six lower and upper body muscles (Noraxon, 3000 Hz) were collected. Changes to variables between 90% and 70% of VO2max were analyzed using paired sample t-tests. Pearson correlations were used to evaluate the relationships between variables. α was set to 0.05. Results: The O2 extraction was higher for legs than arms at both exercise intensities (p<0.05). The arms O2 extraction decreased more than that of the legs when intensity decreased (p<0.01). Leg and pole peak forces and muscle activity increased with intensity (p<0.01), whereas the impulses of forces and the ratio between the arm and leg force remained constant. O2 extraction was negatively associated with iEMG activity in % of MVC at both intensities (r=-0.56 to -0.91, p<0.05 to p<0.001). The lactate a-v difference in the arms was associated with the leg impulses at both intensities (r=-0.53 and -0.57, p<0.05) and with a cycle rate at 70 % of VO2max (r=0.77, p<0.01). Discussion: A decreased relative use of the arms and legs’ MVC at a given % of VO2max decreases O2 extraction. The difference in O2 extraction between the arms and legs increased at decreased exercise intensities, mainly due to decreased arm O2 extraction despite similar changes in muscle activity. A high leg impulse decreases lactate occurrence in the arms, regardless of exercise intensity, whereas a low cycle rate is important only during medium intensity DIA. References: Calbet, JA, Holmberg HC, Rosdahl H, van Hall G, Jensen-Urstad M, Saltin B. (2005). Why do arms extract less oxygen than legs during exercise? Am J Physiol Regul Integr Comp Physiol, 289, R1448-1458. Van Hall G, Jensen-Urstad M, Rosdahl H, Holmberg HC, Saltin B, Calbet JA. (2003). Leg and arm lactate and substrate kinetics during exercise. Am J Physiol Endocrinol Metab, 284, E193-205. Endurance training and sprint performance in elite junior cross-country skiers Authors: Sandbakk, Ø., Welde, B., Holmberg, H.C. Institutions: 1 North-Troendelag University College, Dep. of Sport and Physical Education, 2 Swedish Winter Sports Research Centre, 3 Human Movement Science Programme NTNU, Country: Norway Introduction: Sprint races in modern cross-country (XC) skiing have a shorter racing time, as well as a relatively flat terrain profile, when compared to traditional races. Several studies have thus suggested that maximal speed is the most important performance predictor (e.g. Stöggl et al., 2007). However, the energy release for comparable racing times in other sports is reported to be 70-85% aerobic (Gastin, 2001). The present study therefore investigated the importance of aerobic capacity in sprint performance. The effects of a major change in training stimuli, due to increased emphasis on high-speed moderate intensive endurance training upon sprint performance, maximal O2-uptake (VO2max) and O2-uptake at the ventilatory threshold (VO2VT) were also examined. Methods: Fifteen (10 males and 5 females) elite junior XC skiers (age 17.4±0.5 yr, VO2max 68±6 ml kg-1 min-1) participated in this study. After an eight week baseline training period, all subjects performed a freestyle 1.5 km sprint time-trial on roller skis. In addition, VO2max and VO2VT were measured in the laboratory. Thereafter, an eight week intervention training period was performed. Subjects were split into a control group (CG, n=8) and an intervention group (IG, n=7). The IG increased their training at intensities near the ventilatory threshold, emphasizing level and mixed terrain in order to induce more high-speed training, while the CG continued their traditional polarized training model with 70-80% slow distance training and the remainder as high-intensity interval training. After the intervention training period the sprint race and tests on VO2max and VO2VT, were rerun. Results: Close relationships were found between VO2max (r = -0.79, p<0.01) and VO2VT (r = -0.67, p<0.01) and sprint performance. The mean sprint time in all athletes was 3:36±0:19 min in the pre-test. The IG improved sprint performance by 4.5±2.9% (p<0.01), VO2max by 3.9±1.9% (p<0.01) and VO2VT by 9.9±3.1% (p<0.01) from pre- to post-test. No significant changes were found in the CG. Discussion: Our findings suggest an association between sprint performance and aerobic capacity. The improvements in the IG are potentially related to the major change in training stimuli and demonstrate the effects of training at these moderate intensities, as well as the importance of training periodization. Additionally, some of the improvements might have been induced by the high speed rather than the effects of the exercise intensity. References: Gastin, P. Energy system interaction and relative contribution during maximal exercise. Sports Med, 31 (10):725-741, 2001. Stöggl T, Lindinger S, Müller E. Analysis of a simulated sprint competition in classical cross-country skiing.
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