Double poling kinematic changes during the course of a long-distance race: effect of performance level

ABSTRACT

We aimed to evaluate the changes in double poling (DP) kinematics due to a long-distance cross-country skiing race in athletes with different performance levels. A total of 100 cross-country skiers, belonging to 10 different performance groups, were filmed on flat terrain 7 and 55 km after the start line, during a 58-km classical race. Cycle velocity, frequency and length decreased from the best to the lower-ranked group, while duty cycle increased (all P <.001). Between track sections, cycle velocity and length decreased, duty cycles increased (all P <.001) while frequency was unaltered (P =.782). Group*section interactions resulted for cycle velocity (P =.005). Considering all the participants together, % change in cycle velocity between sections correlated with % change in length and duty cycle (all P <.001). Thus i) skiers in better groups showed longer and more frequent cycles as well as shorter duty cycles than skiers in slower groups; ii) throughout the race all the groups maintained the same cycle frequency while decreasing cycle velocity and length; iii) better groups showed a lower reduction in cycle velocity. Individually, a low reduction in cycle velocity during the race related to the capacity to maintain long cycles and short duty cycles.     

Scaling of upper-body power output to predict time-trial roller skiing performance

Abstract

The purpose of the present study was to establish the most appropriate allometric model to predict mean skiing speed during a double-poling roller skiing time-trial using scaling of upper-body power output. Forty-five Swedish junior cross-country skiers (27 men and 18 women) of national and international standard were examined. The skiers, who had a body mass (m) of 69.3 ± 8.0 kg (mean ± s), completed a 120-s double-poling test on a ski ergometer to determine their mean upper-body power output (W). Performance data were subsequently obtained from a 2-km time-trial, using the double-poling technique, to establish mean roller skiing speed. A proportional allometric model was used to predict skiing speed. The optimal model was found to be: Skiing speed = 1.057 · W ^0.556 · m ^?0.315, which explained 58.8% of the variance in mean skiing speed (P < 0.001). The 95% confidence intervals for the scaling factors ranged from 0.391 to 0.721 for W and from ?0.626 to ?0.004 for m. The results in this study suggest that allometric scaling of upper-body power output is preferable for the prediction of performance of junior cross-country skiers rather than absolute expression or simple ratio-standard scaling of upper-body power output.     

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.     

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.     

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.     

The effects of skiing velocity on mechanical aspects of diagonal cross-country skiing

Cycle and force characteristics were examined in 11 elite male cross-country skiers using the diagonal stride technique while skiing uphill (7.5°) on snow at moderate (3.5 ± 0.3 m/s), high (4.5 ± 0.4 m/s), and maximal (5.6 ± 0.6 m/s) velocities. Video analysis (50 Hz) was combined with plantar (leg) force (100 Hz), pole force (1,500 Hz), and photocell measurements. Both cycle rate and cycle length increased from moderate to high velocity, while cycle rate increased and cycle length decreased at maximal compared to high velocity. The kick time decreased 26% from moderate to maximal velocity, reaching 0.14 s at maximal. The relative kick and gliding times were only altered at maximal velocity, where these were longer and shorter, respectively. The rate of force development increased with higher velocity. At maximal velocity, sprint-specialists were 14% faster than distance-specialists due to greater cycle rate, peak leg force, and rate of leg force development. In conclusion, large peak leg forces were applied rapidly across all velocities and the shorter relative gliding and longer relative kick phases at maximal velocity allow maintenance of kick duration for force generation. These results emphasise the importance of rapid leg force generation in diagonal skiing.     

Combined metabolic gas analyser and dGPS analysis of performance in cross-country skiing

The purpose of this study was to provide a more detailed analysis of performance in cross-country skiing by combining findings from a differential global positioning system (dGPS), metabolic gas measurements, speed in different sections of a ski-course and treadmill threshold data. Ten male skiers participated in a freestyle skiing field test (5.6?km), which was performed with dGPS and metabolic gas measurements. A treadmill running threshold test was also performed and the following parameters were derived: anaerobic threshold, threshold of decompensated metabolic acidosis, respiratory exchange ratio = 1, onset of blood lactate accumulation and peak oxygen uptake ([Vdot]O_2peak). The combined dGPS and metabolic gas measurements made detailed analysis of performance possible. The strongest correlations between the treadmill data and final skiing field test time were for [Vdot]O_2peak (l?·?min^?1), respiratory exchange ratio = 1 (l?·?min^?1) and onset of blood lactate accumulation (l?·?min^?1) (r = ?0.644 to ??0.750). However, all treadmill test data displayed stronger associations with speed in different stretches of the course than with final time, which stresses the value of a detailed analysis of performance in cross-country skiing. Mean oxygen uptake ([Vdot]O₂) in a particular stretch in relation to speed in the same stretch displayed its strongest correlation coefficients in most stretches when [Vdot]O₂ was presented in units litres per minute, rather than when [Vdot]O₂ was normalized to body mass (ml?·?kg^?1?·?min^?1 and ml?·?min^?1?·?kg^?2/3). This suggests that heavy cross-country skiers have an advantage over their lighter counterparts. In one steep uphill stretch, however, [Vdot]O₂ (ml?·?min^?1?·?kg^?2/3) displayed the strongest association with speed, suggesting that in steep uphill sections light skiers could have an advantage over heavier skiers.     

Determination of the centre of mass kinematics in alpine skiing using differential global navigation satellite systems

In the sport of alpine skiing, knowledge about the centre of mass (CoM) kinematics (i.e. position, velocity and acceleration) is essential to better understand both performance and injury. This study proposes a global navigation satellite system (GNSS)-based method to measure CoM kinematics without restriction of capture volume and with reasonable set-up and processing requirements. It combines the GNSS antenna position, terrain data and the accelerations acting on the skier in order to approximate the CoM location, velocity and acceleration. The validity of the method was assessed against a reference system (video-based 3D kinematics) over 12 turn cycles on a giant slalom skiing course. The mean (± s) position, velocity and acceleration differences between the CoM obtained from the GNSS and the reference system were 9 ± 12 cm, 0.08 ± 0.19 m · s^-1 and 0.22 ± 1.28 m · s^-2, respectively. The velocity and acceleration differences obtained were smaller than typical differences between the measures of several skiers on the same course observed in the literature, while the position differences were slightly larger than its discriminative meaningful change. The proposed method can therefore be interpreted to be technically valid and adequate for a variety of biomechanical research questions in the field of alpine skiing with certain limitations regarding position.     

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.     

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.     

Biomechanical pole and leg characteristics during uphill diagonal roller skiing

Diagonal skiing as a major classical technique has hardly been investigated over the last two decades, although technique and racing velocities have developed substantially. The aims of the present study were to 1) analyse pole and leg kinetics and kinematics during submaximal uphill diagonal roller skiing and 2) identify biomechanical factors related to performance. Twelve elite skiers performed a time to exhaustion (performance) test on a treadmill. Joint kinematics and pole/plantar forces were recorded separately during diagonal roller skiing (9°; 11 km/h). Performance was correlated to cycle length (r = 0.77; P < 0.05), relative leg swing (r = 0.71), and gliding time (r = 0.74), hip flexion range of motion (ROM) during swing (r = 0.73) and knee extension ROM during gliding (r = 0.71). Push-off demonstrated performance correlations for impulse of leg force (r = 0.84), relative duration (r = ? 0.76) and knee flexion (r = 0.73) and extension ROM (r = 0.74). Relative time to peak pole force was associated with performance (r = 0.73). In summary, diagonal roller skiing performance was linked to 1) longer cycle length, 2) greater impulse of force during a shorter push-off with larger flexion/extension ROMs in leg joints, 3) longer leg swing, and 4) later peak pole force, demonstrating the major key characteristics to be emphasised in training.     

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。     

我国越野滑雪裁判员队伍发展现状及培养对策研究

随着越野滑雪裁判队伍的逐渐壮大,我国越野滑雪裁判员在成长过程中也有一些急需解决的问题。以我国越野滑雪裁判员为研究对象,运用文献资料法、专家访谈、调查问卷、数理统计法对越野滑雪裁判员人员结构、年龄结构、文化结构等进行调查研究,找出越野滑雪裁判员不足和需要加强的方面,从而使我国越野滑雪裁判员水平得到提高,为今后发展我国越野滑雪提供人才储备,为我国裁判队伍做好培养工作。     

我国越野滑雪项目科研现状与发展策略

我国越野滑雪运动的科研水平对提升越野滑雪项目的成绩具有重要的作用。对2000～2010年我国越野滑雪运动的科研论文在科研论文刊载情况、研究类型、研究内容和研究方法等方面进行分析与研究,认为目前存在研究整体发展水平滞后、研究方法单一、研究与训练实践相脱节等问题。并针对我国越野滑雪项目的科研现状,提出注重软科学、跨学科与交叉融合的研究,扩大研究主题与研究对象;引进先进技术、研究工具和研究方法;充分利用基础研究的成果加强实践性研究等发展对策提高我国越野滑雪运动的科研水平。     

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。     

Quantifying instantaneous performance in alpine ski racing

Abstract

Alpine ski racing is a popular sport in many countries and a lot of research has gone into optimising athlete performance. Two factors influence athlete performance in a ski race: speed and the chosen path between the gates. However, to date there is no objective, quantitative method to determine instantaneous skiing performance that takes both of these factors into account. The purpose of this short communication was to define a variable quantifying instantaneous skiing performance and to study how this variable depended on the skiers' speed and on their chosen path. Instantaneous skiing performance was defined astime loss per elevation difference dt/dz, which depends on the skier's speed v(z), and the distance travelled per elevation difference ds/dz. Using kinematic data collected in an earlier study, it was evaluated how these variables can be used to assess the individual performance of six ski racers in two slalom turns. The performance analysis conducted in this study might be a useful tool not only for athletes and coaches preparing for competition, but also for sports scientists investigating skiing techniques or engineers developing and testing skiing equipment.     

Biomechanical analysis of the “running” vs. “conventional” diagonal stride uphill techniques as performed by elite cross-country skiers

PurposeThis study aimed to compare biomechanical aspects of a novel “running” diagonal stride (DS_RUN) with “conventional” diagonal stride (DS_CONV) skiing techniques performed at high speed.MethodsTen elite Italian male junior cross-country skiers skied on a treadmill at 10 km/h and at a 10° incline utilizing both variants of the diagonal stride technique. The 3-dimensional kinematics of the body, poles, and roller skis; the force exerted through the poles and foot plantar surfaces; and the angular motion of the leg joints were determined.ResultsCompared to DS_CONV, DS_RUN demonstrated shorter cycle times (1.05 ± 0.05 s vs. 0.75 ± 0.03 s (mean ± SD), p < 0.001) due to a shorter rolling phase (0.40 ± 0.04 s vs. 0.09 ± 0.04 s, p < 0.001); greater force applied perpendicularly to the roller skis when they had stopped rolling forward (413 ± 190 N vs. 890 ± 170 N, p < 0.001), with peak force being attained earlier; prolonged knee extension, with a greater range of motion during the roller ski-stop phase (28° ± 4° vs. 16° ± 3°, p = 0.00014); and more pronounced hip and knee flexion during most of the forward leg swing. The mechanical work performed against friction during rolling was significantly less with DS_RUN than with DS_CONV (0.04 ± 0.01 J/m/kg vs. 0.10 ± 0.02 J/m/kg, p < 0.001).ConclusionOur findings demonstrate that DS_RUN is characterize by more rapid propulsion, earlier leg extension, and a greater range of motion of knee joint extension than DS_CONV. Further investigations, preferably on snow, should reveal whether DS_RUN results in higher acceleration and/or higher peak speed.     

Biomechanical aspects of new techniques in alpine skiing and ski-jumping

Abstract

There have been considerable changes in equipment design and movement patterns in the past few years both in alpine skiing and ski-jumping. These developments have been matched by methods of analysing movements in field conditions. They have yielded new insights into the skills of these specific winter sports. Analytical techniques have included electromyography, kinetic and kinematic methods and computer simulations. Our aim here is to review biomechanical research in alpine skiing and ski-jumping. We present in detail the techniques currently used in alpine skiing (carving technique) and ski-jumping (V-technique), primarily using data from the authors’ own research. Finally, we present a summary of the most important results in biomechanical research both in alpine skiing and ski-jumping. This includes an analysis of specific conditions in alpine skiing (type of turn, terrain, snow, speed, etc.) and the effects of equipment, materials and individual-specific abilities on performance, safety and joint loading in ski-jumping.     

3周1550 m亚高原训练对优秀青年男子越野滑雪运动员生理机能和身体成分影响研究

目的:探究3周海拔1550 m亚高原训练对优秀青年男子越野滑雪运动员生理机能和身体成分的影响,并且提出针对性的备战训练建议。方法:国家越野滑雪集训队10名优秀青年男子越野滑雪运动员[年龄(18.7±1.5)岁,身高(78.5±5.8)cm,体质量(66.6±4.7)kg]在亚高原(海拔1550 m)进行3周训练,并在亚高原训练前后对运动员的生理机能和身体成分进行系列测试。使用重复方差分析对运动员数据进行自身比较。结果:运动员由平原初上亚高原时,乳酸阈测试血乳酸浓度显著提升(P<0.05),最大摄氧量和红细胞浓度显著降低(P<0.05)。经过3周训练后,运动员的乳酸阈测试血乳酸浓度和最大摄氧量显著下降(P<0.05),全身总质量、上肢肌肉质量和下肢脂肪质量显著提升(P<0.05)。结论:由平原初上亚高原时,运动员乳酸阈能力和最大摄氧能力显著降低。3周亚高原训练后,运动员的乳酸阈能力和上肢肌肉水平显著提升,最大摄氧能力下降幅度明显。建议:在进行亚高原训练时,我国优秀青年越野滑雪运动员应当注重对心肺摄氧能力的训练,并且注意提升周平均高强度训练(high intensity training,HIT)训练总时间,以维持和提升最大摄氧能力。     

3周1550 m亚高原训练对优秀青年男子越野滑雪运动员生理机能和身体成分影响研究

目的:探究3周海拔1550 m亚高原训练对优秀青年男子越野滑雪运动员生理机能和身体成分的影响,并且提出针对性的备战训练建议。方法:国家越野滑雪集训队10名优秀青年男子越野滑雪运动员[年龄(18.7±1.5)岁,身高(78.5±5.8)cm,体质量(66.6±4.7)kg]在亚高原(海拔1550 m)进行3周训练,并在亚高原训练前后对运动员的生理机能和身体成分进行系列测试。使用重复方差分析对运动员数据进行自身比较。结果:运动员由平原初上亚高原时,乳酸阈测试血乳酸浓度显著提升(P<0.05),最大摄氧量和红细胞浓度显著降低(P<0.05)。经过3周训练后,运动员的乳酸阈测试血乳酸浓度和最大摄氧量显著下降(P<0.05),全身总质量、上肢肌肉质量和下肢脂肪质量显著提升(P<0.05)。结论:由平原初上亚高原时,运动员乳酸阈能力和最大摄氧能力显著降低。3周亚高原训练后,运动员的乳酸阈能力和上肢肌肉水平显著提升,最大摄氧能力下降幅度明显。建议:在进行亚高原训练时,我国优秀青年越野滑雪运动员应当注重对心肺摄氧能力的训练,并且注意提升周平均高强度训练(high intensity training,HIT)训练总时间,以维持和提升最大摄氧能力。