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- Hegge, Ann Magdalen, et al.
(author)
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Comparison of the g3 and g4 skating techniques in cross-country skiing
- 2013
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In: Proceeding for the the 6<sup>th</sup> International Congress on Science and Skiing. - 9783200034174 ; , s. 94-
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Conference paper (peer-reviewed)abstract
- INTRODUCTION: The five predominant skating techniques employed in cross-country skiing can be classified from gear 1 to 5, where the skier’s speed and incline of the track determine the gear chosen. The third (G3) and fourth gears (G4) both involve symmetrical double poling, but G3 includes two poling actions per cycle (i.e., poling together with each leg push-off) and G4 only one (i.e., poling together with the leg push-off on the strong side and a forward arm swing in combination with the leg push-off on the weak side). Our purpose was to directly compare these two techniques, which, to the best of our knowledge, has not yet been done.METHODS: Fifteen elite male cross-country skiers (age 24 ± 4 yrs, body mass 74 ± 7 kg, body height 180 ± 5 cm, VO2peak 70.6 ± 4.2 ml·min-1·kg-1) performed 4 minutes of submaximal roller skiing using the G3 skating technique at 14 km h-1 on a 5% incline and 4 minutes of submaximal roller skiing using the G4 skating technique at 20 km h-1 on a 2% incline on two consecutive days. Based on previous testing and training, these inclines were considered most appropriate for each specific technique, and the selected speeds achieved equal exercise intensities (oxygen uptake: 51.4 ± 2.5 and 51.5 ± 4.6 ml·min-1·kg-1, and blood lactate: 2.7 ± 1.1 and 2.5 ± 1.5 mmol·L-1 for G3 and G4, respectively). In addition to physiological responses, cycle characteristics, the resultant ski forces and other ski kinetics were measured.RESULTS AND DISCUSSION: Work rate was 22% higher with G3 (203 ± 20 versus 167 ± 17 W, P<0.001), resulting in an absolute difference in gross efficiency of 2.4% (15.3 ± 0.8 versus 12.9 ± 1.3%, P<0.001), primarily an effect of incline. Cycle time was longer (2.04 ± 0.15 versus 1.73 ± 0.11 sec) and thus the cycle rate lower (0.50 ± 0.04 versus 0.58 ± 0.05 Hz) with G3. With G3, approximately 60% of the cycle time was spend with the ski on the ground and 40% in the ski swing phase without any significant differences between both skis. In G4, significant differences between the strong and weak side were found with a relative ground contact time of approximately 66% for the strong side and 59% for the weak side (P<0.001). Differences between the strong and weak side in G4 were also found in the resultant ski forces (with 7% higher peak forces on the weak side), the center of pressure on the skis, the speed of the skis (with a 15% lower speed of the weak side ski at ski lift-off) and the orientation angle to the forward direction (with a wider angle of the weak side ski during the entire ground contact phase). All of these differences could be explained by the effect of poling on the strong side and the poling recovery phase with a forward arm swing on the weak side. In the case of G3, there were no such differences between the two skis.CONCLUSION: This study revealed distinct differences between the G3 and G4 skating techniques, such that the former can be regarded as symmetrical and the latter as asymmetrical. It was found that poling influences the leg work considerably. Furthermore, with G4 significant differences between the two skis were detected, a novel finding not reported previously.
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- Holmberg, Hans-Christer, 1958-
(author)
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INTEGRATIVE BIOMECHANICS AND PHYSIOLOGY IN C-C SKIING
- 2013
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In: Proceedings for the 6<sup>th</sup> International Congress on Science and Skiing. - 9783200034174 ; , s. 7-7
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Conference paper (peer-reviewed)abstract
- Because they possess well-developed and unique physical capacities, cross-country (c-c) skiers have been of special interest for research in exercise science [1,2]. Early on, much of this research aimed to improve our understanding of the physiological characteristics of the athletes and the energy demands made on them in connection with various modes of skiing. As the sport has evolved, technical aspects have received more and more attention and combining physiological and biomechanical approaches have provided new insights. C-c skiing involves several different techniques, a complexity that presents considerable technical, as well as cognitive challenges during a race. In response to changes in velocity, the inclination of the slope, and snow conditions, the skier must often choose between techniques that differ with respect to kinematics, kinetics, and the distribution of the workload between the muscles of the upper and lower body. Recent investigations on the physiology associated with the mechanical demands made by these techniques has revealed much about the responses of the arms and legs to the competing requirements placed by different types of exercise. Furthermore, elite skiers demonstrate unique combinations of well-developed aerobic and anaerobic capacities. Moreover, both their upper and lower extremities are capable of generating high forces and power and the muscles there contain rich capillary beds and abundant mitochondria, factors that exert an appreciable influence on the performance of endurance sports.To date, most research on c-c skiing has been performed in the laboratory and more studies in the field/on snow and/or during competition are desirable [3]. Such evaluations would provide insights into the factors that determine performance in connection with the various racing disciplines, as well as into why and when skiers use the different techniques. They should also clarify further the significance of pacing and the differences between roller-skiing and skiing on snow. Fortunately, recent technological advances and innovations, with lighter equipment and higher accuracy, allow the recording of velocity and position with enhanced precision, providing biomechanical measurements in real time and more rapid feedback to the athlete.Clearly, integration of biomechanical and physiological approaches and application of modern technology have tremendous potential to reveal new information concerning the factors the determine performance in c-c skiing, thereby helping to improve this performance.REFERENCES1. Calbet JA, Jensen-Urstad M, van Hall G, Holmberg HC, Rosdahl H, Saltin B. Maximal muscular vascular conductances during whole body upright exercise in humans. Journal of Physiology. 2004. 558(Pt 1):319-31. 2. Holmberg H-C, Rosdahl H, Svedenhag J. Lung function, arterial saturation and oxygen uptake in elite cross country skiers: influence of exercise mode. Scandinavian Journal of Medicine and Science in Sports. 2007. 17(4):437-44.3. Sandbakk O, Holmberg H-C. A Reappraisal of Success Factors for Olympic Cross-Country Skiing. International Journal of Sports Physiology and Performance. 2013.
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- Jensen, Kurt, et al.
(author)
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Changes in physical performance parameters during and after moderate altitude training in elite cross country skiers
- 2013
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In: Proceedings for the 6<sup>th</sup> International Congress on Science and Skiing. - 9783200034174 ; , s. 115-
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Conference paper (peer-reviewed)abstract
- INTRODUCTION: The Olympic cross country skiing competitions in 2014 will be held in Sochi, Russia at an altitude of approximately 1500m. Although moderate, this altitude is known to reduce performance in highly trained endurance athletes. It is also known that individuals react differently during altitude exposure. The purpose of this study was to evaluate performance changes during and after three weeks of training in moderate altitude in elite skiers.METHOD: Four male and three female skiers were tested on a roller skiing treadmill using the classic technique at sea level (NORM1), after 3 and 20 days at 1500m altitude (ALT1 and ALT2), and 10 days after altitude at sea level (NORM2). The test protocol was a standardized progressive submaximal session of 4 min exercise with 1 min rest between each stage, followed by a 6-10 min progressive “all out” exercise with an increase in first speed and then grade every minute. Oxygen uptake (VO2) was measured continuously during submaximal and maximal exercise. Blood lactate concentrations were measured during the 1 min rest between submax stages and 2 min after the max test. Power at each submax and max stage were calculated from roller ski friction and body weight against gravity [1]. Each stage power was further used for calculations of power at VO2max, (WVO2max), work efficiency at submaximal loads (GE) and for the estimation of O2 cost at maximal work load (used to calculate accumulated O2 deficit (MOD)) [2].RESULTS: At NORM1, the skiers’ body mass was 71.9±10.7kg and VO2max 214±12ml/min/kg0.73. The GE varied between 17.9-19.5% during the 3-5 submaximal loads, with no difference between conditions (P>0.05). Also, blood lactate accumulation after submaximal exercise loads showed no difference between conditions (P<0.05). At ALT1, the VO2max and the WVO2max decreased 8.9% and 9.1%, respectively (P<0.05), however there were no differences between ALT1 and ALT2 or from NORM1 and NORM2 (P>0.05). In contrast, the average power output (322±87W) during the “all out” test increased 3.4±2.7% 10 days after the altitude training (P<0.05). Average MOD varied between 57-79 mlO2·kg-1 over the training period, but with no change between conditions (P>0.05). The coefficient of variation (CV%) for the changes in MOD between NORM1 and 2 was 40%.DISCUSSION: This study demonstrated that performance (VO2max, WVO2max) deteriorates by 8-9% in a group of elite skiers training at a moderate altitude corresponding to 1500m. No increase in any of the physiological parameters related to performance included in the study was seen after moderate altitude training, except for the maximal power which increased 3.4%. The response after moderate altitude training seems to be related more to anaerobic than aerobic factors. However, this was not confirmed by the MOD in this group of highly trained skiers. The large CV for change in MOD reflects the individual responses to this training.CONCLUSION: Small changes of 2-3% in performance in highly trained in elite skiers after moderate altitude training seems not to be related to any single parameter. One should not ignore individual differences in adaptation. REFERENCES1. Ainegren, M. et al Engineering of Sport 7, Vol 2, 2008: p. 393-400.2. Medbo, J.I.et al J.Appl.Physiol., 1988. 64: p. 50-60.
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| 11. |
- Swarén, Mikael, et al.
(author)
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Repetitive Low Impacts on Alpine Ski Helmets
- 2013
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In: Proceedings for the 6<sup>th</sup> International Congress on Science and Skiing. - 9783200034174 ; , s. 22-
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Conference paper (peer-reviewed)
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| 13. |
- Örtenblad, Niels, et al.
(author)
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Repeated sprint exercise impairs contractile force of isolated single human muscle fibers
- 2013
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In: Proceedings for the 6<sup>th</sup> International Congress on Science and Skiing. - 9783200034174 ; , s. 93-
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Conference paper (peer-reviewed)abstract
- INTRODUCTION: The purpose of the present study was, to examine the effects of repeated sprint skiing on the contractile apparatus of single muscle fibres obtained from a group of elite skiers. We have recently demonstrated that prolonged cycling exercise impairs the contractile apparatus of single muscle fibres, and that this can be restored following recovery. However, little is known about the effect of repeated high intensity exercise on single fibre properties, as i.e. during cross-country (cc) sprint competitions. We hypothesize that repeated high intensity exercise in highly trained subjects will impair the contractile apparatus maximum force output.METHOD: Eleven elite male sprint talented cc skiers (age 24 ± 4 years; VO2max 5.1 ± 0.5 (diagonal skiing, DIA), 4.9 ± 0.5 (double pooling, DP) L·min-1)) volunteered for the study. The skiers performed a simulated intermittent classic sprint roller skiing competition on a treadmill. The sprint exercise included 4 times1300m, with 45 min recovery between sprints. Each sprint consisted of 3 DP sections (1° uphill) and 2 DIA sections (7° uphill). Muscle biopsies were obtained in arm muscle (m. biceps brachii) before and after the sprint exercises. Muscle fibre bundles were cooled and skinned in a glycerinating solution and stored until analyzed. Single muscle fibre segments (n=232) were isolated and attached to a sensitive force recording transducer, and activated by Ca2+ buffered solutions at pH 7.1 to measure mechanically properties (maximum force Po and Po/cross sectional area (CSA)) and fibre typed by the Sr2+ sensitivity (Hvid et al. 2013).RESULTS: Average sprint time was 3min 49s ± 9s, with no difference between sprints. A total of 232 fibres were analysed (150 type I and 82 type II fibres). Type II fibres had a sign. (P<0.05) higher CSA (8103 ± 2334 µm2 (type I) and 8852 ± 2288 µm2 (type II) and Po (0.82 ± 0.43 and 1.24 ± 0.50 mN) than type I fibres. Also type II fibres had a 31% higher Po/CSA (108 ± 55 vs 142 ± 45 kN/m2). Following the intermittent sprint exercise, type II fibres exhibited a sign. (P = 0.01) 20% decrease in Po, with no difference in type I fibres. To test if the decrease in the single fibre Po were associated with oxidative stress we tested if this could be reversed with a strong reducing agent (dithiothreitol, DTT). DTT did not alter Po at pre nor the decrease in type II fibres following sprint exercise.DISCUSSION: By using a translational approach from whole body exercise to single fibre measurements, we here we demonstrate that type II fibres from highly trained cross country skiers, has a 20% decrease in Po following repeated sprint. Thus, part of the experienced fatigue following sprint competitions is due to impairments at the level of the contractile apparatus. Further, we did not find any evidence for oxidative stress as a causative component in the observed decrease in Po.CONCLUSION: Here we demonstrate for the first time, in highly trained sprint skiers, that repeated sprint impairs single fibre maximum force at the level of the contractile apparatus, which may have a significant impact on muscle function and fatigue.REFERENCES: Gejl K, Hvid LG, Ulrik Frandsen U, Jensen K, Sahlin K and Ørtenblad N. Muscle glycogen content modifies SR Ca2+ release rate in elite endurance athletes. Med. Sci. Sports Ex. (2013).
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