Energy cost of different skating techniques in cross-country skiing

The aims of this study were to compare the aerobic energy cost of four 'on-snow' skating techniques in cross-country skiing and to examine the relationships between performance and aerobic energy cost. Twelve male skiers from recreational to national standard performed four level skating trials of 6 min duration in random order, each at the same submaximal velocity but with a different skating technique: (1) 'offset' (V1), using a double asymmetrical and asynchronous pole plant as weight is transferred to one ski; (2) 'two-skate' (V2A), where the pole plant is symmetrical; (3) 'one-skate' (V2), where there is a pole plant as weight is transferred to each ski; and (4) 'conventional', without poles. Oxygen uptake (VO2), pulmonary ventilation, the respiratory exchange ratio and heart rate were measured using a K4(b2) portable gas analyser. The aerobic energy cost (VO2/mean speed) and heart rate were higher (P < 0.05) in the one-skate than in the offset condition. This may be explained by the greater and more efficient use of the upper body and the lower variation in centre of gravity velocity in the offset condition. The aerobic energy cost was 5-9% higher (P < 0.01) in the conventional than in the other techniques, probably because of the shorter duration of propulsive forces within a cycle in the conventional skating condition. Moreover, in ski skating, the mechanical efficiency (propulsive forces/total forces) was shown to be higher in the upper than in the lower limbs. The correlation coefficient between performance and aerobic energy cost was significant in the two-skate (r = 0.68, P = 0.02), one-skate (r = 0.72, P = 0.01) and conventional (r = 0.62, P = 0.04) conditions, but not in the offset condition (r = 0.50, P = 0.10). Our results stress the importance of the upper body component in cross-country skiing and that the aerobic energy cost discriminates between skiers of different standards.     

Biomechanical comparison of the double-push technique and the conventional skate skiing technique in cross-country sprint skiing

The aims of the study were to: (1) adapt the "double-push" technique from inline skating to cross-country skiing; (2) compare this new skiing technique with the conventional skate skiing cross-country technique; and (3) test the hypothesis that the double-push technique improves skiing speed in a short sprint. 13 elite skiers performed maximum-speed sprints over 100 m using the double-push skate skiing technique and using the conventional "V2" skate skiing technique. Pole and plantar forces, knee angle, cycle characteristics, and electromyography of nine lower body muscles were analysed. We found that the double-push technique could be successfully transferred to cross-country skiing, and that this new technique is faster than the conventional skate skiing technique. The double-push technique was 2.9 +/- 2.2% faster (P < 0.001), which corresponds to a time advantage of 0.41 +/- 0.31 s over 100 m. The double-push technique had a longer cycle length and a lower cycle rate, and it was characterized by higher muscle activity, higher knee extension amplitudes and velocities, and higher peak foot forces, especially in the first phase of the push-off. Also, the foot was more loaded laterally in the double-push technique than in the conventional skate skiing technique.     

Biomechanical comparison of the double-push technique and the conventional skate skiing technique in cross-country sprint skiing

Abstract

The aims of the study were to: (1) adapt the “double-push” technique from inline skating to cross-country skiing; (2) compare this new skiing technique with the conventional skate skiing cross-country technique; and (3) test the hypothesis that the double-push technique improves skiing speed in a short sprint. 13 elite skiers performed maximum-speed sprints over 100 m using the double-push skate skiing technique and using the conventional “V2” skate skiing technique. Pole and plantar forces, knee angle, cycle characteristics, and electromyography of nine lower body muscles were analysed. We found that the double-push technique could be successfully transferred to cross-country skiing, and that this new technique is faster than the conventional skate skiing technique. The double-push technique was 2.9 ± 2.2% faster (P < 0.001), which corresponds to a time advantage of 0.41 ± 0.31 s over 100 m. The double-push technique had a longer cycle length and a lower cycle rate, and it was characterized by higher muscle activity, higher knee extension amplitudes and velocities, and higher peak foot forces, especially in the first phase of the push-off. Also, the foot was more loaded laterally in the double-push technique than in the conventional skate skiing technique.     

Effects of speed on temporal patterns in classical style and freestyle cross-country skiing

The purpose was to study the adaptation to speed in the temporal patterns of the movement cycle and determine any differences in velocity, cycle rate and cycle length at the maximum speed level in the different classical style and freestyle cross-country skiing techniques. Eight skilled male cross-country skiers were filmed with a digital video camera in the sagittal plane while skiing on a flat cross-country ski track. The skiers performed three classical style techniques the diagonal stride, kick double poling and the double poling technique and four freestyle techniques paddle dance (gear 2), double dance (gear 3), single dance (gear 4) and combiskate (gear 5) at four different self-selected speed levels slow, medium, fast and their maximum. Cycle duration, cycle rate, cycle length, and relative and absolute cycle phase duration of the different techniques at the different speed levels were analysed by means of a video analysis system. The cycle rate in all tested classical and freestyle techniques was found to increase significantly (p < .01) with speed from slow to maximum. Simultaneously, there was a significant decrease in the absolute phase durations of all the investigated skiing techniques. A minor, not significant, change in cycle length, and the significant increase in cycle rate with speed showed that the classical and freestyle cross-country skiing styles are dependent, to a large extent, on an increase in cycle rate for speed adaptation. A striking finding was the constant relative phase duration with speed, which indicates a simplified neural control of the speed adaptation in both cross-country skiing styles. For the practitioner, the knowledge about the importance of increasing cycle frequency rather than cycle length in the speed adaptation can be used to optimise a rapid increase in speed. The knowledge about the decrease in absolute phase duration, especially the thrust phase duration, points to the need for strength and technique training to enable force production at a high cycle rate and skiing speed. The knowledge that the relative phase duration stays constant with speed may be used to simplify the learning of the different cross-country skiing techniques.     

冬季两项运动员的生物学特征和竞赛、训练特征研究

理论研究薄弱是我国开展雪上项目的主要掣肘因素,也制约了我国对2022北京冬奥会的备战。本研究从运动员生物学特征、比赛技术及训练角度分析了冬季两项的项目特征,认为形态学的主要特征为身体强壮、体脂率低,运动员在滑行和射击中的主要生理指标特征分别为较高的HR、VO2max、乳酸阈值与机体总工作效率,及良好的身体感知与自我调节能力,运动损伤特征为日常训练多发,女性与7年以上运动员多发,下背部与膝部多发。技术特征方面,滑行中自由滑行技术的G2和G3分技术对成绩影响最大,ML站姿更利于射击中维持身体稳定性,而肩上夹紧枪托及较轻的双手持枪力度更利于持枪稳定性和射击准度。年度体能训练以LIT为主,MIT与HIT比例较低;陆地体能训练中滚轮滑雪比例最高,辅以较高比例蹬车训练,雪上训练以自由滑行G2、G3分技术练习为主;力量训练中,男运动员侧重均衡的上、下肢练习,女运动员侧重上肢力量训练;射击训练多采取分组竞争、模拟比赛的方式进行,并注重训练大风天气下的适应力。     

Biomechanical determinants of cross-country skiing performance: A systematic review

ABSTRACT

Cross-country skiing is a complex endurance sport requiring technical skills, in addition to considerable physiological and tactical abilities. This review aims to identify biomechanical factors that influence the performance of cross-country skiers. Four electronic databases were searched systematically for original articles in peer-reviewed journals addressing the relationship between biomechanical factors (including kinematics, kinetics, and muscle activation) and performance while skiing on snow or roller skiing. Of the 46 articles included, 22 focused exclusively on the classical technique, 18 on the skating technique, and six on both. The indicators of performance were: results from actual or simulated races (9 articles); speed on specific tracts (6 articles); maximal or peak speed (11 articles); skiing economy or efficiency (11 articles); and grouping on the basis of performance or level of skill (12 articles). The main findings were that i) cycle length, most often considered as a major determinant of skiing speed, is also related to skiing economy and level of performance; ii) higher cycle rate related with maximal speed capacity, while self-selected cycle rate improves skiing economy at sub-maximal speeds; iii) cross-country skiing performance appears to be improved by joint, whole-body, ski, and pole kinematics that promote forward propulsion while minimizing unnecessary movement.     

基于运动学特征的越野滑雪专项力量训练器应用机理

利用运动图像解析法,通过与越野滑雪传统式同时推进技术动作的运动学特征进行对比分析,探讨一种新型越野滑雪专项力量辅助训练器的应用机理。发现这种训练器运动学特征与雪上传统式同时推进技术动作存在一定相关性。这种训练器较好地模拟了雪上传统式同时推进技术动作特点,丰富了陆地夏训期传统专项训练方法体系,有助于越野滑雪陆地、雪上专项化训练方法有效衔接。越野滑雪专项力量辅助训练器在运动学特征上对雪上专项技术动作的模拟性,可为发展有效的专项训练方法与手段提供理论依据。     

青少年越野滑雪运动员陆地身体素质训练

为使青少年越野滑雪运动员竞技能力得到全面提高,经过多年训练实践,总结出青少年越野滑雪运动员陆地身体素质训练的具体方法：发展力量素质的训练方法有越野滑轮、拉力训练;发展耐力素质的训练方法有山地越野跑和模仿训练、滑轮场地滑轮训练和利用越野滑雪塑料滑道训练;发展速度素质训练的方法有上坡山地跑和模仿训练和滑轮训练;发展灵敏素质训练的方法有在滑轮比赛场地的锐角弯道处进行滑轮反复训练、小场地足球比赛及传抢游戏、半场篮球比赛等;发展协调素质的训练方法有短距离直道快速侧向跑和立卧撑等。     

An experimental study to compare the grip of classical style roller skis with on-snow skiing

Cross-country skiers use roller skis for their snow-free training with the aim of imitating skiing on snow. Also, exercise laboratories evaluate the biomechanics and physiology of cross-country skiing using roller skis on a treadmill. The roller skis on the market that are constructed for use in the classical style are equipped with a front and a back wheel, one of which has a ratchet to enable it to grip the surface when diagonal striding and kick double poling (static friction). The aim of this study was to investigate static friction coefficients (μ_S) of ratcheted wheel roller skis, and compare the results to the μ_S reported from skiing on snow with grip-waxed cross-country skis. Also, a new type of roller ski with a camber and adjustable grip function was evaluated. The results showed that ratcheted wheel roller skis, on a treadmill rubber mat and on dry and wet asphalt surfaces, reached μ_S values that were five to eight times greater than the values reported from on-snow skiing with grip-waxed cross-country skis. For the roller skis with a camber and adjustable grip function, the μ_s could be varied from no grip at all up to the level of the tested ratcheted wheel roller skis.     

A simple mechanical model for simulating cross-country skiing,skating technique

The role of simulation models in sport disciplines has become relevant lately due to the multiple advantages that they may offer sports teams, coaches and practitioners. This paper develops and presents a simple three-dimensional multibody dynamic model of a cross-country skier, modeling a single propulsion phase to obtain the kinetic parameters involved in the movement. A professional Olympic-level skier performed the skating technique without poles in a ski tunnel under controlled conditions and on an incline plane. Then, with a force acquisition system attached to the ski bindings and a motion capture system set on site, the leg resultant forces and the movement of specific points of the skier’s lower body were acquired. The data obtained from the motion capture system were used as the prescribed kinematic input data in the multibody model and the measured force was used later as a parameter of comparison with the results of the simple model. After simulating the technique, the calculated resultant forces seem to be in agreement with those measured in the field.     

Using micro-sensor data to quantify macro kinematics of classical cross-country skiing during on-snow training

Abstract

Micro-sensors were used to quantify macro kinematics of classical cross-country skiing techniques and measure cycle rates and cycle lengths during on-snow training. Data were collected from seven national level participants skiing at two submaximal intensities while wearing a micro-sensor unit (MinimaxX^?). Algorithms were developed identifying double poling (DP), diagonal striding (DS), kick-double poling (KDP), tucking (Tuck), and turning (Turn). Technique duration (T-time), cycle rates, and cycle counts were compared to video-derived data to assess system accuracy. There was good reliability between micro-sensor and video calculated cycle rates for DP, DS, and KDP, with small mean differences (Mdiff% = ?0.2 ± 3.2, ?1.5 ± 2.2 and ?1.4 ± 6.2) and trivial to small effect sizes (ES = 0.20, 0.30 and 0.13). Very strong correlations were observed for DP, DS, and KDP for T-time (r = 0.87–0.99) and cycle count (r = 0.87–0.99), while mean values were under-reported by the micro-sensor. Incorrect Turn detection was a major factor in technique cycle misclassification. Data presented highlight the potential of automated ski technique classification in cross-country skiing research. With further refinement, this approach will allow many applied questions associated with pacing, fatigue, technique selection and power output during training and competition to be answered.     

Power and pacing calculations based on real-time locating data from a cross-country skiing sprint race

Pacing strategies in cross-country skiing have been investigated in several studies. However, none of the previous studies have been verified by collected skiing data giving the skiing velocities along a measured track. These can be used to calculate the propulsive power output. Collected real-time positioning data from a cross-country sprint skiing race were used to estimate the propulsive power by applying a power balance model. Analyses were made for the time-trial and the final for one female and one male skier. The average propulsive power over the whole race times were 311 and 296 W during the time trial and 400 and 386 W during the final, for the female and male skier, respectively. Compared to the average propulsive power over the whole race, the average active propulsive phases were calculated as 33 and 44% higher in the time trials and 36 and 37% higher in the finals for the female and male, respectively. The current study presents a novel approach to use real-time positioning data to estimate continuous propulsive power during cross-country sprint skiing, enabling in-depth analyses of power output and pacing strategies.     

Evaluation of a specific test in cross-country skiing

Six Danish male cross-country skiers were studied during the end-of-summer and winter seasons. Their maximal oxygen uptake was measured while running on a treadmill and using a ski ergometer incorporating the double-poling technique. Maximal oxygen uptake during treadmill running and double-poling was correlated with performance, expressed as a ranking score during 10 ski races. The tests were undertaken in September, December and April. Upper body maximal oxygen uptake increased 5.8% from September to December, decreasing to 2.3% above the September level in April. Upper body work output (2 min at maximal intensity) increased 11.8% from September to December (P less than 0.05). The relationship between upper body and leg maximal oxygen uptake--the upper body/leg ratio--was 89.4% in September. In four skiers, both treadmill and upper body tests were undertaken on each test occasion. The upper body/leg ratio changed from 87.7% in September to 95.7% in December. In April, the ratio was 91.0%. The maximal oxygen uptake measured using the ski ergometer during double-poling was significantly correlated with performance (P less than 0.05). It is concluded that the upper body ski ergometer can be used in the evaluation of elite cross-country skiers.     

Forward acceleration of the centre of mass during ski skating calculated from force and motion capture data

The purpose of this paper was to present and evaluate a methodology to determine the contribution of bilateral leg and pole thrusts to forward acceleration of the centre of mass (COM) of cross-country skiers from multi-dimensional ground reaction forces and motion capture data. Nine highly skilled cross-country (XC) skiers performed leg skating and V2-alternate skating (V2A) under constant environmental conditions on snow, while ground reaction forces measured from ski bindings and poles and 3D motion with high-speed cameras were captured. COM acceleration determined from 3D motion analyses served as a reference and was compared to the results of the proposed methodology. The obtained values did not differ during the leg skating push-off, and force–time curves showed high similarity, with similarity coefficients (SC) >0.90 in the push-off and gliding phases. In V2A, leg and pole thrusts were shown to contribute 35.1 and 65.9% to the acceleration of the body, respectively. COM acceleration derived from ground reaction forces alone without considering the COM position overestimated the acceleration compared to data from motion analyses, with a mean difference of 17% (P < 0.05) during leg push-off, although the shapes of force–time curves were similar (SC = 0.93). The proposed methodology was shown to be appropriate for determining the acceleration of XC skiers during leg skating push-off from multi-dimensional ground reaction forces and the COM position. It was demonstrated that both the COM position and ground reaction forces are needed to find the source of acceleration.     

不同地形越野滑雪自由滑行技术的运用

越野滑雪运动员根据滑雪场地不同地形的需要,熟练运用最合理的滑行技术可以减小雪板与雪地之间的摩擦力和空气阻力,达到以最小的体能代价获得最佳运动速度的目的。分析越野滑雪运动员在不同滑道地形自由滑行技术的特点,探讨运动员在各种地形中使用自由滑行技术的合理性,并在训练中针对平原——缓上坡——缓下坡——陡上坡等地势变化的具体情况,培养运动员合理运用自由滑行技术,使越野滑雪运动员取得更优异的运动成绩。     

Fatigue in a simulated cross-country skiing sprint competition

Abstract

The aim of this study was to assess fatigue during a simulated cross-country skiing sprint competition based on skating technique. Sixteen male skiers performed a 30-m maximal skiing speed test and four 850-m heats with roller skies on a tartan track, separated by 20 min recovery between heats. Physiological variables (heart rate, blood lactate concentration, oxygen consumption), skiing velocity, and electromyography (EMG) were recorded at the beginning of the heats and at the end of each 200-m lap during the heats. Maximal skiing velocity and EMG were measured in the speed test before the simulation. No differences were observed in skiing velocity, EMG or metabolic variables between the heats. The end (820–850 m) velocities and sum-iEMG of the triceps brachii and vastus lateralis in the four heats were significantly lower than the skiing velocity and sum-iEMG in the speed test. A significant correlation was observed between mean oxygen consumption and the change in skiing velocity over the four heats. Each single heat induced considerable neuromuscular fatigue, but recovery between the heats was long enough to prevent accumulation of fatigue. The results suggest that the skiers with a high aerobic power were less fatigued throughout the simulation.     

我国越野滑雪运动可持续发展论略

在分析我国越野滑雪现状的基础上,指出我国在越野滑雪项目上已取得的成绩及与世界先进水平的差距。目前我国越野滑雪项目存在专业队伍较少,各地重视不足;运动员水平与世界先进水平存在差距;场地设施、器材装备及科研辅助不足等一系列问题,并针对上述问题提出将越野滑雪短距离竞速项目纳入全运会金牌榜,吸引社会参与越野滑雪;加强同高水平国家交流;加强科研服务及保障;争取器材装备赞助,加快其国产化;加大推广普及力度,开展学校教学等措施,以期为我国越野滑雪项目的进一步发展提供参考。     

越野滑雪运动员运动性疲劳的恢复

越野滑雪是周期性耐力项目,运动时间多、距离长,能量消耗大,对运动员的心理和机体能力要求较高。越野滑雪运动员的运动训练恢复是运动训练中的重要组成部分,良好的消除疲劳方法,能提高运动水平。结合越野滑雪运动训练实践,运用理论分析方法阐述越野滑雪运动疲劳产生的机理和检测方法,并提出恢复训练、营养补充和心理训练等方法,旨在为促进越野滑雪运动员运动疲劳的积极恢复提供理论依据。     

Changes in the cross-country ski base properties resulting from the ski use

In this work, changes in the cross-country ski base properties resulting from stone grinding, skiing, waxing and re-stone grinding have been investigated. The surface topography, crystallinity, wettability and sliding properties of cross-country ski bases were recorded using a selection of measurement techniques: non-contact chromatic confocal microscopy, contact-type surface roughness analyser and scanning electron microscopy (topography), Raman spectroscopy (crystallinity), contact angle measurement (wettability) and a ski tester (sliding properties). The tested skis were used for 150 km and waxed 35 times. The ski base surface became smoother and the orientation and crystallisation of the base material increased. Wear decreased the hydrophobicity and increased the sliding friction. Even though re-grinding did not restore all of the ski base properties, re-grinding improved the wettability and sliding properties. The results help to optimise stone grinding interval to maintain the performance of the skis.     

世界级短距离越野滑雪运动员专项体能特征研究进展及启示

短距离越野滑雪是一项比赛强度高、轮次多、赛间间歇短的体能类项目,是我国备战2022年北京冬奥会的重要突破口。主要基于英文文献,探寻世界级短距离越野滑雪运动员专项体能特征,为提升我国该项目专项体能的科学训练水平提供参考。研究发现：1）世界级短距离越野滑雪男女运动员的身高分别为175~188 vs.166~176 cm,体重为70~92 vs.55~70 kg,瘦体重占比接近83 vs.70%;2）比赛中的能量供应以有氧代谢为主,并呈现有氧无氧动态交替主导;3）具有较高平均滑行速度和连续"多赛"能力,在起滑和冲刺阶段的速度最快,高速滑行中上、下肢呈现明显的"爆发式"用力特征,躯干力量对各种技术动作运用具有重要影响。为此,国家队冬奥备战科技助力应围绕专项体能突破展开重点攻关,深入探寻影响比赛高速滑行保持能力的生理学与运动学因素,加快提升比赛表现水平。