首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 140 毫秒
1.
In this study, we measured the vertical and horizontal take-off forces, plantar pressures and activation patterns of four muscles (vastus lateralis, gluteus maximus, tibialis anterior, gastrocnemius) in 10 ski jumpers in simulated laboratory conditions when wearing either training shoes or ski jumping boots. We found significant differences in vertical (P < 0.001), horizontal (P < 0.05) and resultant (P < 0.001) take-off velocities and vertical force impulse (P < 0.01). We found no significant differences in the jumpers' initial take-off positions; however, the jumping boots condition resulted in a smaller displacement in the final position of the following joint angles: ankle angle (P < 0.001), knee angle (P < 0.001), hip angle (P < 0.01) and shank angle relative to the horizontal (P < 0.01). This corresponds with less electromyographic activity during take-off in both the gastrocnemius (300 to 200 ms and 200 to 100 ms before take-off) and gluteus maximus (300 to 200 ms and 100 to 0 ms before take-off). During the early take-off in the jumping boots condition, significantly more pressure was recorded under the heel (P < 0.001), whereas the forefoot was more highly loaded at the end of the take-off. Differences in take-off velocity (representing the final output of the take-off) can be accounted for in the main by the different use of plantar flexion, emphasizing the role of the knee and hip extensors when wearing jumping boots. We conclude that the stiffness of the structure of the jumping boots may result in a forward shift of pressure, thus limiting the effective vertical force. To avoid this pressure shift, the pattern of movement of simulated take-offs should be carefully controlled, particularly when wearing training shoes.  相似文献   

2.
We propose a new method, based on inertial sensors, to automatically measure at high frequency the durations of the main phases of ski jumping (i.e. take-off release, take-off, and early flight). The kinematics of the ski jumping movement were recorded by four inertial sensors, attached to the thigh and shank of junior athletes, for 40 jumps performed during indoor conditions and 36 jumps in field conditions. An algorithm was designed to detect temporal events from the recorded signals and to estimate the duration of each phase. These durations were evaluated against a reference camera-based motion capture system and by trainers conducting video observations. The precision for the take-off release and take-off durations (indoor < 39 ms, outdoor = 27 ms) can be considered technically valid for performance assessment. The errors for early flight duration (indoor = 22 ms, outdoor = 119 ms) were comparable to the trainers' variability and should be interpreted with caution. No significant changes in the error were noted between indoor and outdoor conditions, and individual jumping technique did not influence the error of take-off release and take-off. Therefore, the proposed system can provide valuable information for performance evaluation of ski jumpers during training sessions.  相似文献   

3.
  相似文献   

4.
As hill jumps are very time-consuming, ski jumping athletes often perform various imitation jumps during training. The performed jumps should be similar to hill jumps, but a direct comparison of the kinetic and kinematic parameters has not been performed yet. Therefore, this study aimed to correlate 11 common parameters during hill jumps (Oberstdorf Germany), squat jumps (wearing indoor shoes), and various imitation jumps (rolling 4°, rolling flat, static; jumping equipment or indoor shoes) on a custom-built instrumented vehicle with a catch by the coach. During the performed jumps, force and video data of the take-off of 10 athletes were measured. The imitation and squat jumps were then ranked. The main difference between the hill jumps and the imitation and squat jumps is the higher maximal force loading rate during the hill jumps. Imitation jumps performed on a rolling platform, on flat ground were the most similar to hill jumps in terms of the force–time, and leg joint kinematic properties. Thus, non-hill jumps with a technical focus should be performed from a rolling platform with a flat inrun with normal indoor shoes or jumping equipment, and high normal force loading rates should be the main focus of imitation training.  相似文献   

5.
ABSTRACT

Imitation jumps are frequently used in training for ski jumping. Yet, the dynamics of these jumps differ considerably. Thus, the relevance of imitation jumps for ski jumping performance is not elucidated. The aim of this study was to investigate the relationship between the technical execution of imitation jumps and ski jumping performance level. We compared the imitation jumps of 11 ski jumpers of different performance levels using a Spearman correlation transform of time traces of the kinetics (measured using force cells and motion capture) of imitation jumps. The kinetic aspects that were related to performance centred on the moment arm of ground reaction force to the centre of mass before the onset of the push-off, angular momentum early in push-off, thigh angle during the main period of push-off and vertical velocity towards the end of push-off. We propose that the thigh angle may be a key element allowing high development of linear momentum while preparing for appropriate aerodynamic position. Furthermore, the findings suggest that the kinetic development prior to (and during) push-off is more important than the kinematic end state at take-off.  相似文献   

6.
There are differences in ground reaction force when wearing soccer boots compared with training shoes on a natural turf surface. Two natural-turf-covered force platforms, located outdoors in a field, allowed comparison of performance when six-studded soccer boots and soccer training shoes were worn during straight fast running (5.4 m s-1 ± 0.27 m s-1) and slow running (4.4 ms-1 ± 0.22 m s-1). Six male soccer players (mean age: 25 ± 4.18 years; mean mass 79.7 ±9.32 kg) struck the first platform with the right foot and the second platform with the left foot. In fast running, the mean vertical impact peak was significantly greater in soccer boots (2.706 BW) than in training shoes (2.496 BW) when both the right and left foot were considered together and averaged (P = 0.003). Similarly, the mean vertical impact peak loading rate was greater when wearing soccer boots at 26.09 BWs-1 compared to training shoes (21.32 BWs-1;P = 0.002). Notably, the mean vertical impact peak loading rate of the left foot (boots: 28.07 BWs-1; shoes: 22.52 BWs-1) was significantly greater than the right foot (boots: 24.11 BWs-1; shoes: 20.11 BWs-1) in both boots and shoes (P = 0.018). The braking force was greater for the left foot (P = 0.013). In contrast, mean peak vertical propulsion forces were greater for the right foot (P > 0.001) when either soccer boots or training shoes were considered. Similar significant trends were evident in slow running, and, notably, in both soccer boots and training shoes medial forces were greater for the left foot (P = 0.008) and lateral forces greater for the right foot (P = 0.011). This study showed the natural turf ground reaction force measurement system can highlight differences in footwear in an ecological environment. Greater forces and impact loading rates occurred during running activity in soccer boots than in training shoes, with soccer boots showing reduced shock attenuation at impact. Such findings may have implications for impact-related injuries with sustained exposure, especially on harder natural-turf surfaces. There were differences in the forces occurring at the right and left feet with the ground, thus suggesting the use of bipedal monitoring of ground reaction forces.  相似文献   

7.
跳远起跳最佳效果的特征主要体现在起跳的腾起水平速度(在一定腾起角度状态下)，而起跳腾起的水平速度来于助跑的质量，其中主要表现在起跳前几步助跑的速度、节奏和助跑技术。通过教学实验，反映出无板助跑起跳练习对起跳前几步助跑的速度感、节奏感的效果比有板起跳练习的效果要好，这对形成起跳的最佳效果无疑是有积极的影响。从而可以加大起跳腾空阶段身体重心通过的水平距离，它对提高跳远运动成绩将起到决定性的作用。  相似文献   

8.
  相似文献   

9.
This study examined the effects of the rider on the linear projectile kinematics of show-jumping horses. SVHS video recordings (50 Hz) of eight horses jumping a vertical fence 1 m high were used for the study. Horses jumped the fence under two conditions: loose (no rider or tack) and ridden. Recordings were digitised using Peak Motus. After digitising the sequences, each rider's digitised data were removed from the ridden horse data so that three conditions were examined: loose, ridden (including the rider's data) and riderless (rider's data removed). Repeated measures ANOVA revealed significant differences between ridden and loose conditions for CG height at take-off (p < 0.001), CG distance to the fence at take-off (p = 0.001), maximum CG during the suspension phase (p < 0.001), CG position over the centre of the fence (p < 0.001), CG height at landing (p < 0.001), and vertical velocity at take-off (p < 0.001). The results indicated that the rider's effect on jumping horses was primarily due to behavioural changes in the horses motion (resulting from the rider's instruction), rather than inertial effects (due to the positioning of the rider on the horse). These findings have implications for the coaching of riders and horses.  相似文献   

10.
The purpose of this study was to examine the effects of calendar and skeletal age, anthropometric dimensions, training history and their interactions on vertical jumping height and horizontal overhead throwing velocity in a cross-section of 318 young male athletes (age range 9-16 years) participating in cross-country skiing (n = 70), basketball (n = 40), apparatus gymnastics (n = 19), ice hockey (n = 50), track and field (n = 89) and wrestling (n = 50). Vertical jumping height was measured with four different loads held on the shoulders and then interpolated for loads representing 0 and 40% body mass. Horizontal overhead throwing velocity using both hands was determined for seven balls of different weights and then interpolated for weights representing 1 and 5% body mass. Both vertical jumping height and overhead throwing velocity were found to increase (P < 0.01) from the skeletally youngest to the oldest cohort when the effects of body height and mass were controlled. The inter-event comparisons did not reveal statistically significant differences in respect of vertical jumping height. Also in the overhead throwing tests, the inter-event differences were small, although the analysis of variance revealed statistically significant (P < 0.001) differences for the skeletal age cohorts of 13 and 14 years. While the quantity of training had no effect on vertical jumping height, it explained the results in the overhead throwing test. The effects of training on vertical jumping and horizontal overhead throwing among adolescent athletes were considered to be small, while maturational processes and anthropometric development followed by increase in calendar age were deemed to be of greater importance.  相似文献   

11.
Abstract

Dorsiflexion sport shoes aim to increase jumping capacity and speed by means of a lower position of the heel in comparison with the forefoot, favouring additional stretching of the ankle plantar flexors. In previous studies, contradictory results have been found on the benefits of using this type of shoe. With the aim of comparing a dorsiflexion sport shoe model (DF) with a conventional sport shoe (CS), 41 participants performed a countermovement jump (CMJ) test and an agility test (MAT) with both models of shoe. There were no significant differences in the jump test [CS=35.3 cm (6.4) and DF=35.6 cm (6.4), P>0.05]. In the agility test, the conventional shoe obtained better results than the model with dorsiflexion with regard to time taken to complete the circuit [CS=6236 ms (540) and DF=6377 ms (507), P<0.05)]. In spite of producing pre-stretching of the plantar muscles, the DF sport shoes were not effective for improving either jump power or agility in a specific test.  相似文献   

12.
Sagittal plane SVHS video recordings (50 Hz) were made of horses jumping the wall at an international Puissance competition. Video sequences were manually digitized and six kinematic variables at take-off were analyzed. Nine horses started the competition with the fence height at 1.80 m, and two horses attempted the fence in the fifth and final round with the fence height at 2.27 m. For successful performances, fence height was correlated with the following take-off variables: vertical velocity of the centre of mass (r = 0.45, p = 0.03); height of centre of mass (r = 0.44, p = 0.04); distance of centre of mass from fence (r = 0.46, p = 0.03); and distance from leading hind limb to centre of mass (r = -0.61, p < 0.01). These results indicated that body position at take-off is the most important aspect when jumping high fences. This is the first known study that has examined horses jumping over a Puissance wall. The results should help horse riders and trainers improve performance in Puissance jumping horses, and perhaps help in the early selection of horses with a talent for jumping high fences.  相似文献   

13.
Twelve participants ran (9 km · h(-1)) to test two types of running shoes: replica and original shoes. Ground reaction force, plantar pressure and electromyographic activity were recorded. The shoes were tested randomly and on different days. Comparisons between the two experimental conditions were made by analysis of variance (ANOVA) test (P ≤ 0.05). The time to first peak, loading rate of the first peak and impulse of the first 75 ms of stance were significantly different between the shoes (P ≤ 0.05), revealing an increase of impact forces for the replica shoes. The peak plantar pressure values were significantly higher (P ≤ 0.05) when wearing replica shoes. During running, the contact area was significantly smaller (P ≤ 0.05) for the replica shoe. The electromyographic activity of the analysed muscles did not show changes between the two shoes in running. These findings suggest that the use of replica running shoes can increase the external load applied to the human body, but may not change the muscle activity pattern during locomotion. This new mechanical situation may increase the risk of injuries in these movements.  相似文献   

14.
Ski jumping flight posture was analyzed for achieving large flight distance on the basis of high-speed video images of the initial 40 m part of 120-m ski jumping flight. The time variations of the forward leaning angle and the ski angle of attack were measured from the video images, and the aerodynamic forces were calculated from the kinematic data derived from the images. Some correlations were investigated between the initial-speed corrected flight distance and such parameters as the angles of jumper, the initial transition time and the aerodynamic force coefficients. The result indicated that small body angle of attack was a key for large flight distance in the initial phase of flight because of small drag force, and that the most distinctive fault of beginners was too large body angle of attack and ski angle of attack leading to aerodynamic stall. Too small drag force does not give an optimal condition for large flight distance because the lift force is also too small. The ratio of the lift to the drag was larger than 0.95 for advanced jumpers.  相似文献   

15.
Abstract

The purpose of this study was to examine the effects of calendar and skeletal age, anthropometric dimensions, training history and their interactions on vertical jumping height and horizontal overhead throwing velocity in a cross‐section of 318 young male athletes (age range 9–16 years) participating in cross‐country skiing (n = 70), basketball (n = 40), apparatus gymnastics (n = 19), ice hockey (n = 50), track and field (n = 89) and wrestling (n = 50). Vertical jumping height was measured with four different loads held on the shoulders and then interpolated for loads representing 0 and 40% body mass. Horizontal overhead throwing velocity using both hands was determined for seven balls of different weights and then interpolated for weights representing 1 and 5% body mass.

Both vertical jumping height and overhead throwing velocity were found to increase (P< 0.01) from the skeletally youngest to the oldest cohort when the effects of body height and mass were controlled. The inter‐event comparisons did not reveal statistically significant differences in respect of vertical jumping height. Also in the overhead throwing tests, the inter‐event differences were small, although the analysis of variance revealed statistically significant (P< 0.001) differences for the skeletal age cohorts of 13 and 14 years. While the quantity of training had no effect on vertical jumping height, it explained the results in the overhead throwing test.

The effects of training on vertical jumping and horizontal overhead throwing among adolescent athletes were considered to be small, while maturational processes and anthropometric development followed by increase in calendar age were deemed to be of greater importance.  相似文献   

16.
This paper describes the results of a numerical study to determine the optimal flight technique for V-style ski jumping. We attempt to answer the question of how a jumper should fly in order to increase their flight distance in a V-style posture. The index of performance in this optimization study is the horizontal flight distance, which is mathematically equivalent to the total flight distance, and the control parameters are the ski-operning angle and the angle of forward lean that the jumper employs (the body-ski angle). The flight trajectory is simulated on the basis of an aerodynamic database constructed from wind tunnel test data. It is found that the ski-opening angle should be increased in the first half of the flight, and then maintained at a constant value during the rest of the jump. Optimal control of the ski-opening angle when there is either a headwind or tailwind is also discussed. It is found that the jumper needs to control the skiopening angle over a wider range in the case of a headwind than in the case of a tailwind. The jumper's skill in controlling the ski-opening angle is very important for increasing the flight distance, especially in the case of a tailwind.  相似文献   

17.
To determine the flight of a ski jumper it is essential to know what aerodynamic forces are acting on the ski jumper. However, few data on this are available, especially for a V-style ski jumping flight. We have measured the aerodynamic forces during the free flight phase for a V-style, as well as a parallel-style, ski jump by employing a full-size model in a wind tunnel. The aerodynamic force data, (drag, lift and pitching moment) were obtained to create an aerodynamic database. These forces are given in polynomial form as functions of the angle of attack, the body-ski (forward leaning) angle and the ski-opening (V-style) angle. Using the polynomial form database is a convenient way of obtaining the aerodynamic forces. Moreover, the wind tunnel was equipped with a ground effect plate to measure the aerodynamic forces during the landing phase. It was found that the difference between the lift with and without the ground effect plate increases with the ski-opening angle. The longitudinal stability in the pitching motion of a body-ski combination is also discussed on the basis of the pitching moment data. This indicates that a stable pitching oscillation of the body-ski combination may arise around an equilibrium point in the angle of attack, the trim angle of attack, during flight.  相似文献   

18.
The aim of this study was to establish the effectiveness of a resistance training programme, designed to improve vertical jumping ability, on the grab, swing and rear-weighted track starts in swimming. Twenty-three female non-competitive swimmers participated (age 19.9 +/- 2.4 years; mean +/- s). The diving techniques were practised weekly for 8 weeks. The participants were randomly assigned to a control group (n = 11) or a resistance-training group (n = 12), which trained three times a week for 9 weeks. The tests before and after the training programme involved performing each dive technique and six dry-land tests: two countermovement jumps (with and without arms), two isokinetic squats (bar speeds of 0.44 and 0.70 rad x s(-1)) and two overhead throws (with andwithout back extension). A repeated-measures multivariate analysis of variance was used to show that resistance training improved performance in the dry-land tests (P < 0.0001). No significant improvements due to training were found for any temporal, kinematic or kinetic variables within the grab or swing starts. Significant improvements (P < 0.05) were found for the track start for take-off velocity, take-off angle and horizontal impulse. The results suggest that the improved skill of vertical jumping was not transferred directly to the start, particularly in the grab technique. Non-significant trends towards improvement were observed within all starts for vertical force components, suggesting the need to practise the dives to retrain the changed neuromuscular properties.  相似文献   

19.
目的：对3种不同深蹲模式进行肌电测试,以期探讨不同模式下动作的合理性,为教学、训练提供一定的理论依据。方法：本文运用文献资料法、实验法和数理统计法对不同模式的肌电测试进行对比分析研究。结果：动作模式1与动作模式2相比,股内侧肌、股直肌、股外侧肌、臀大肌有非常显著性差异（P〈0.01）,股二头肌有显著性差异（P〈0.05）。动作模式1与动作模式3相比,股内侧肌、股直肌、股外侧肌、臀大肌有非常显著性差异（P〈0.01）,股二头肌有显著性差异（P〈0.05）。动作模式2与动作模式3相比,股内侧肌、臀大肌有非常显著性差异（P〈0.01）,股直肌、股外侧肌有显著性差异（P〈0.05）,股二头肌没有显著性差异（P〉0.05）。结论：3种不同模式深蹲动作的股外侧肌、股直肌、股内侧肌、股二头肌、臀大肌的积分肌电数值表现出显著性差异,动作模式3优于其它两种动作模式。在深蹲训练中强调臀部肌肉的主动收缩,才能更好的提高下肢力量的作用。  相似文献   

20.
采用德国Novel公司的Pedar鞋垫式(in-sole)足底压力测量系统,对40名中学生赤足与穿着慢跑鞋在1.5m·s-1、3.0m·s8-1和5.0m·s-13个速度下的步态周期、最大地面反作用力、最大足底压强、平均足底压强和力量-时间积分值进行分析,探讨赤足运动与穿鞋运动的生物力学特性,以及引起赤足和穿鞋运动之间差异的原因,为指导青少年健康运动提供科学、可靠的参考依据.研究结果证实,赤足运动与穿鞋运动在步态、用力方式、压力分布上都存在显著差异,穿着慢跑鞋运动可有效降低运动损伤出现的几率,为青少年的健康运动提供基础保障.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号