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1.
Net efficiency of roller skiing with a diagonal stride   总被引：1，自引：0，他引：1  
The aims of this study were: (a) to determine net efficiency during roller skiing with a diagonal stride at various speeds; (b) to assess the development of net efficiency across speeds; and (c) to examine the characteristics of efficiency in diagonal roller skiing. Two-dimensional kinematics and oxygen uptake were determined in eight male collegiate cross-country ski athletes who roller skied with the diagonal stride at various speeds on a level track. Net efficiency was calculated from rates of internal and external work and net energy expenditure. Individual net efficiency ranged from 17.7% to 52.1%. Net efficiency in the entire group of athletes increased with increasing speed, reached a maximum value of 37.3% at 3.68?m?·?s(-1), before slowly decreasing. These findings indicate that roller skiing with the diagonal stride at high speed is a highly efficient movement and that an optimal speed exists at which net efficiency can be maximally enhanced in diagonal roller skiing.  相似文献   

2.
Commercial systems utilizing data from inertial measurement units (IMUs) to analyse movement patterns have not yet been adapted to monitor daily training in cross-country (XC) skiing. The main purposes of this study are to investigate: (1) the feasibility and potential of a multi-sensor system consisting of a heart rate sensor, global navigation satellite systems (GNSSs) data and seven IMUs placed at multiple locations on the body for outdoor XC skiing, and (2) the validity of employing hard decision rules based on the correlation between arms and legs for detecting sub-techniques in classical XC skiing. All sensor data were synchronously sampled and synchronized with GNSS data from a commercially available sports watch while XC skiing on varying tracks, from amateur skiers and world-class athletes. An algorithm based on the correlation of the angular velocity of arms and legs was developed to detect the three main classic sub-techniques, diagonal, double poling with a kick and double poling. Other sub-techniques were classified as miscellaneous (0–20%). The system is shown to work well outdoors on snow during different conditions, and the implemented algorithm was validated by video analyses to detect the three sub-techniques with a sensitivity of 99–100%. This study is the first to detect and link sub-techniques in XC skiing to GNSS data, thereby associating the detection and distribution of sub-techniques to different terrains. Such information gives insight into the technical and tactical aspects of skiers’ daily training and competitions, thereby providing a tool for coaches and athletes.  相似文献   

3.
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.  相似文献   

4.
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 (μS) of ratcheted wheel roller skis, and compare the results to the μS 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 μS 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 μs could be varied from no grip at all up to the level of the tested ratcheted wheel roller skis.  相似文献   

5.
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.  相似文献   

6.
In this study, changes in skiing performance and poling kinetics during a simulated cross-country sprint skiing competition were investigated. Twelve elite male cross-country skiers performed simulated sprint competition (4 × 1,150 m heat with 20 min recovery between the heats) using the double-poling technique. Vertical and horizontal pole forces and cycle characteristics were measured using a force plate system (20-m long) during the starting spurt, racing speed, and finishing spurt of each heat. Moreover, heat and 20-m phase velocities were determined. Vertical and horizontal pole impulses as well as mean cycle length were calculated. The velocities of heats decreased by 2.7 ± 1.7% (p = 0.003) over the simulated competition. The 20-m spurting velocity decreased by 16 ± 5% (p < 0.002) and poling time increased by 18 ± 9% (p < 0.003) in spurt phases within heats. Vertical and horizontal poling impulses did not change significantly during the simulation; however, the mean forces decreased (p < 0.039) (vertical by 24 ± 11% and horizontal by 20 ± 10%) within heats but not between the heats. Decreased heat velocities over the simulated sprint and spurting velocities within heats indicated fatigue among the skiers. Fatigue was also manifested by decreased pole force production and increased poling time.  相似文献   

7.
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.  相似文献   

8.
我国冬奥雪上竞速类项目的竞技水平与世界优势国家存在较大差距。拟基于冬奥雪上竞速类项目的国际文献,探究世界级运动员的关键竞技特征及其训练策略,为我国雪上项目2022年冬奥备战冲刺年的精准训练明晰目标导向。研究显示：世界级雪上竞速类项目运动员核心技术动作的经济性更高,表现为越野滑雪平地双杖推撑的周期更长、周期速度降低更少,高山滑雪卡宾转弯的半径更短;各单项的能量代谢类型差异显著,但均具备高度发展的有氧、无氧及相互转换能力;快速推蹬时的下肢爆发力、控制姿态时的平衡能力以及持续高速时的速度耐力等运动素质表现更为突出。世界级雪上竞速类项目运动员的关键训练策略在于注重可穿戴等前沿技术多源采集并反馈动作参数,强调高原训练和间歇训练突出有氧代谢能力提升,加大移植引进及创新等多种路径融合发展训练方法,从而有力促进竞训水平的提升。  相似文献   

9.
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.  相似文献   

10.
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.  相似文献   

11.
An inertial measurement unit (IMU) is widely considered to be an economical alternative to capture human motion in daily activities. Use of an IMU for clinical study, rehabilitation, and in the design of orthoses and prostheses has increased tremendously. However, its use in defining running gait is limited. This study presents a practical method to estimate running spatial and temporal parameters using an inertial sensor by placing it on a shoe. A combination of a zero-crossing method and thresholding is used to identify foot-strike and foot-off based on foot acceleration during running. Stride time, ground contact time and flight time can then be identified. An off-phase segmentation algorithm is applied to estimate stride length and running speed. These two parameters are commonly used to evaluate running efficiency and to differentiate elite runners. This study found that an IMU can estimate foot-strike and foot-off with average absolute time differences of 2.60–6.04 and 2.61–16.28 ms, respectively. Stride time was estimated with error between ? 4.04 and 0.33 ms. Stride length and running speed were estimated with maximum average errors of 45.97 mm and 0.41 km/h.  相似文献   

12.
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.  相似文献   

13.
Abstract

The aim of the present study was to examine the effects of movement intensity and path linearity on global positioning system (GPS) distance validity and reliability. One participant wore eight 1-Hz GPS receivers while walking, jogging, running, and sprinting over linear and non-linear 200-m courses. Five trials were performed at each intensity of movement on each 200-m course. One receiver was excluded from analysis due to errors during data collection. The results from seven GPS receivers showed the mean (±s) and percent bias of the GPS distance values on the 200-m linear course were 205.8 ± 2.4 m (2.8%), 201.8 ± 2.8 m (0.8%), 203.1 ± 2.2 m (1.5%), and 205.2 ± 4 m (2.5%) for the walk, jog, run, and sprint trial respectively. Walk and sprint distances were significantly different from jogging and running distances (P < 0.05). The GPS distance values on the 200-m non-linear course were 198.9 ± 3.5 m (?0.5%), 188.3 ± 2 m (?5.8%), 184.6 ± 2.9 m (?7.7%), and 180.4 ± 5.7 m (?9.8%) for the walk, jog, run, and sprint trial respectively; these were significantly lower than those for the corresponding values on the linear course (P < 0.05). Differences between all non-linear movement intensities were significant (P < 0.05). The overall coefficient of variation within and between receivers was 2.6% and 2.8% respectively. Path linearity and movement intensity appear to affect GPS distance accuracy via inherent positioning errors, update rate, and conditions of use; reliability decreases with movement intensity.  相似文献   

14.
This study sought to establish perceptions of elite endurance athletes on the role and worth of altitude training. Elite British endurance runners were surveyed to identify the altitude and hypoxic training methods utilised, along with reasons for use, and any situational, cultural and behaviour factors influencing these. Prior to the 2012 Olympics Games, 39 athletes and 20 support staff (coaches/practitioners) completed an internet-based survey to establish differences between current practices and the accepted “best-practice”. Almost all of the athletes (98%) and support staff (95%) surveyed had utilised altitude and hypoxic training, or had advised it to athletes. 75% of athletes believed altitude and hypoxia to be a “very important” factor in their training regime, with 50% of support staff believing the same. Athletes and support staff were in agreement of the methods of altitude training utilised (i.e. 'hypoxic dose’ and strategy), with camps lasting 3–4 weeks at 1,500–2,500 m being the most popular. Athletes and support staff are utilising altitude and hypoxic training methods in a manner agreeing with research-based suggestions. The survey identified a number of specific challenges and priorities, which could provide scope to optimise future altitude training methods for endurance performance in these elite groups.  相似文献   

15.
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。  相似文献   

16.
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。  相似文献   

17.
The purpose of this study was to investigate the influence of ski slope grade, skiing speed, skiing ability, sex, and age on HR, RPE, and energy expenditure responses during recreational alpine skiing. Thirty-eight participants were divided by age, sex, and skiing ability. Instructor- and self-paced skiing conditions were conducted on 10° and 19.8° slopes. Skiing HR was recorded, RPE collected at the end of each run, and energy expenditure calculated. The pertinent results of this study demonstrate that the interactions of grade × speed, speed × age, and grade × age and the main effects of speed and grade significantly influenced %HRmax, mean HR, RPE, and energy expenditure during skiing. When %HRmax is taken into account, the older skiers skied at a greater relative intensity than the young skiers. The sex, age, and skiing ability main effects did not have a significant influence on mean HR, RPE, and energy expenditure. These data demonstrates that increased speed and grade results in increased physiological stress. Using mean, HR data may not be the best option for assessing physiological stress during exercise in the older athlete as it does not account for the influence of the ageing process.  相似文献   

18.
PurposeThis study aimed to compare biomechanical aspects of a novel “running” diagonal stride (DSRUN) with “conventional” diagonal stride (DSCONV) 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 DSCONV, DSRUN 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 DSRUN than with DSCONV (0.04 ± 0.01 J/m/kg vs. 0.10 ± 0.02 J/m/kg, p < 0.001).ConclusionOur findings demonstrate that DSRUN is characterize by more rapid propulsion, earlier leg extension, and a greater range of motion of knee joint extension than DSCONV. Further investigations, preferably on snow, should reveal whether DSRUN results in higher acceleration and/or higher peak speed.  相似文献   

19.
This study aimed to compare knee joint position sense of roller hockey players with an age-matched group of non-athletes. Forty-three male participants voluntarily participated in this cross-sectional study: 21 roller hockey players (mean age: 23.2 ± 4.2 years old, mean weight: 81.8 ± 9.8 kg, mean height: 180.5 ± 4.1 cm) and 22 age-matched non-athletes (mean age: 23.7 ± 3.9 years old, mean weight: 85.0 ± 6.2 kg, mean height: 181.5 ± 5.0 cm). Knee joint position sense of the dominant limb was evaluated using a technique of open-kinetic chain and active knee positioning. Joint position sense was reported using absolute, relative and variable angular errors. The main results indicated that the group of roller hockey players showed significantly lower absolute (2.4 ± 1.2º vs. 6.5 ± 3.2º, p ≤ 0.001) and relative (1.7 ± 2.1º vs. 5.8 ± 4.4º, p ≤ 0.001) angular errors in comparison with the non-athletes group. In conclusion, the results from this present study suggest that proprioceptive acuity, assessed by measuring joint position sense, is increased in roller hockey players. The enhanced proprioception of the roller hockey players could contribute to injury prevention and improved performance during sporting activities.  相似文献   

20.
The purpose of the investigation was to study the relationship between thrust phase duration, ground reaction force, velocity increase after pole thrust and pole angles versus pole length during double poling in roller skiing. Seven male regional elite cross-country skiers volunteered as subjects for the study. The subjects performed a maximal double pole thrust on roller skis with each of the three different pole lengths: 'short', self-selected (normal) and 'long'. The short and long poles were 7.5 cm shorter and 7.5 cm longer than the self-selected pole length. The subjects made seven maximal pole thrusts with each pole length, which were randomly selected during 21 trials. For each trial the subjects accelerated from a 1.2 m high downhill slope attaining a speed of 3.92 m.s-1 before making a maximal double pole thrust on a force plate placed at the bottom of the slope. The vertical (F2), anterior-posterior (Fy) and mediolateral (Fx) reaction forces of the left pole were measured by the force plate. The positions of the pole were recorded in 3-D by an opto-electronic system. Thrust phase duration, impulse, mean force, velocity increase after pole thrust and pole angles were calculated from the recorded data. Double poling with long poles produced a significantly larger propulsive anterior-posterior reaction force impulse and velocity increase than normal (p < .05) and short poles (p < .05). This was in spite of a larger mean anterior-posterior reaction force being produced with short poles. Thus, thrust phase duration was a primary factor in determining propulsive anterior-posterior impulse. For the practitioner, the results can be useful in the selection of pole length when the aim is to increase thrust phase duration, anterior-posterior force impulse and velocity.  相似文献   

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