Biomechanical loading in the triple jump     

Jarmo Perttunen  Heikki Kyrolainen  Paavo V. Komi  Ari Heinonen 《Journal of sports sciences》2013,31(5):363-370

The triple jump is a demanding field event in which a jumper must tolerate extremely high impact forces while maintaining high horizontal speed. The present study was designed to clarify the mechanical loading characteristics and the role of neuromuscular function in the triple jump. Seven national triple jumpers (4 males, 3 females) volunteered to perform 3-6 jumps. The mean best performances were 14.32 - 0.45 m and 11.90 - 0.28 m for males and females, respectively. The three longest triple jumps for each jumper were selected for final analysis. The mean contact times were 0.139 s (hop), 0.157 s (step) and 0.177 s (jump). The largest ground reaction forces were observed in the step (15.2 times body weight), while the highest peak pressures were recorded under the heel and forefoot. The plantar pressure of the lateral side of the forefoot was highly related to the length of the triple jump ( P ? 0.05-0.01). In addition, electromyograms of both legs suggested that mechanical loading places high demands on the neuromuscular system, as characterized by the high rate of activation in the pre-activity phase followed by high eccentric activity. Thus, the high activities of the gastrocnemius, vastus lateralis and hip extensor muscles seem to play an important role in preventing unnecessary yielding of the jumper during the braking phase.  相似文献   

The continuous measurement of the springboard reaction force in gymnastic vaulting     

Shinya Sano  Yasuo Ikegami  Hiroyuki Nunome  Tommy Apriantono  Shinji Sakurai 《Journal of sports sciences》2013,31(4):381-391

Abstract

A new method was established for the continuous measurement of force applied from a springboard to a gymnast in vaulting (board reaction force). Male gymnasts performed a handspring vault using a springboard mounted on force platforms. A high-speed video camera sampled the springboard motion at 500 Hz. The springboard was initially partitioned into 29 segments. The force due to the accelerative motion of the springboard was determined by summing the forces of the individual segments. The board reaction force acting on the gymnast was calculated by subtracting the force due to the accelerative motion of the springboard and weight from the force recorded by the force platform. The new method succeeded in illustrating transient changes of the board reaction force. The horizontal and vertical components of the peak values of the board reaction force were three and two times greater respectively than the average values. A series of tests was conducted to determine whether the number of segments of the springboard model could be reduced without affecting accuracy. A model consisting of only four segments produced almost the same accuracy as the 29-segment model. The simplified model is recommended as a more efficient method to measure board reaction force.  相似文献   

Temporal and kinetic analysis of unilateral jumping in the vertical,horizontal, and lateral directions     

César M. P. Meylan  Kazunori Nosaka  Jonathon Green  John B. Cronin 《Journal of sports sciences》2013,31(5):545-554

Abstract

The aims of this study were to: (1) assess the reliability of various kinetic and temporal variables for unilateral vertical, horizontal, and lateral countermovement jumps; (2) determine whether there are differences in vertical ground reaction force production between the three types of jumps; (3) quantify the magnitude of asymmetry between limbs for variables that were established as reliable in a healthy population and whether asymmetries were consistent across jumps of different direction; and (4) establish the best kinetic predictor(s) of jump performance in the vertical, horizontal, and lateral planes of motion. Thirty team sport athletes performed three trials of the various countermovement jumps on both legs on two separate occasions. Eccentric and concentric peak force and concentric peak power were the only variables with acceptable reliability (coefficient of variation = 3.3–15.1%; intra-class correlation coefficient = 0.70–0.96). Eccentric and concentric peak vertical ground reaction force (14–16%) and concentric peak power (45–51%) were significantly (P < 0.01) greater in the vertical countermovement jump than in the horizontal countermovement jump and lateral countermovement jump, but no significant difference was found between the latter two jumps. No significant leg asymmetries (–2.1% to 9.3%) were found in any of the kinetic variables but significant differences were observed in jump height and distance. The best single predictors of vertical countermovement jump, horizontal countermovement jump, and lateral countermovement jump performance were concentric peak vertical power/body weight (79%), horizontal concentric peak power/body weight (42.6%), and eccentric peak vertical ground reaction force/body weight (14.9%) respectively. These findings are discussed in relation to monitoring and developing direction-specific jump performance.  相似文献   

Effects of stance angle on postural stability and performance with national-standard air pistol competitors     

《European Journal of Sport Science》2013,13(5):483-489

Abstract

The effects of stance angle on postural stability and shooting processes were studied using eight national-standard male air-pistol shooters. Each shooter performed 60 shots each in four stance angles (0°, 15°, 30° and 45° from the line of fire). Postural stability was determined by measuring change in centre of pressure with a dual-force platform system assessing centre-of-pressure (COP) excursion (average difference of the centre of pressure from the mean) and COP speed (total COP path divided by time). Shooting process measures were determined by using a NOPTEL ST-2000 optoelectronic system. Score was assessed with a Sius Ascor S10 electronic scoring system. The results revealed no significant difference among the various stance angles; COP excursion or COP speed, p>0.05. Results indicated a significant stance angle effect with the shooting process measure, hit fine (percentage of hold within an area the size of the 10-ring when centred over the actual shot; p = 0.025) and the shooting performance measure adjusted score (raw score adjusted for true zero; p=0.008). Moreover, best overall performance was with a stance angle of 15°. These findings suggest that stance angle may affect pistol stability and performance in air-pistol athletes.  相似文献   

Recordkeeping in the First Australian Imperial Force: the political imperative     

Paul Dalgleish 《档案与原稿》2020,48(2):123-141

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测井法探测剩余油方法研究     

张峰 《科技广场》2012,(3):141-144

本文简单介绍了探测剩余油饱和度和分布的方法,对比各自方法的优缺点,最终选择测井方法探测剩余油。从理论出发建立了基于瞬变电磁法的三层柱状介质模型,通过对模型理论的推导及求解,计算出了地层的感应电动势。并通过软件的仿真,直观地说明了发射电流、发射线圈匝数、收发距对感应电动势的影响,验证了此方法探测剩余油的可行性。  相似文献   

淮河流域中游湿地景观格局演变的驱动力分析     

胡巍巍  江涤  徐小梅 《池州师专学报》2011,(3):45-48

淮河流域中游河湖湿地水空间巨大。解放后50年来,淮河流域中游地区湿地萎缩,大量的湿地转变成水田和非湿地,大量的天然湿地演变成人工湿地和非湿地,其中又以作为天然湿地主体的河湖湿地损失最多,并存在河湖湿地-滩地-非湿地的演变过程。通过分析得知,在这50年里,影响淮河流域中游湿地景观格局演变的主要驱动力是土地利用和河流调控两大因素。  相似文献   

论中亚宗教极端势力的基本特征     

苏畅 《新疆师范大学学报(哲学社会科学版)》2011,32(2)

"中亚宗教极端势力"是中亚研究领域中的一个独特、重要的问题.独特性在于,宗教极端主义进入中亚后,与该地区的政治、宗教、民族、文化等因素相结合,形成了独特的复杂性、顽固性和普遍性;重要性在于,宗教极端势力对中亚的影响广泛而纵深:给地区安全和社会稳定带来威胁;是影响中亚政局和中亚国家调整内外政策的因素之一;在人文领域,宗教极端思想影响着新一代中亚人;与"东突"分子相勾结,给中国西北安全带来影响:是中亚地区大国博弈的一个变量因素.  相似文献   

改制射钉枪的检验鉴定方法     

肖敏  熊小东 《乐山师范学院学报》2015,(4)

文章讨论了射钉器的分类、结构与击发机理,指导我们检验改制射钉枪,辨析原射钉器的结构检验和改制部位的检验的方法及重点,最后通过试射实验,判明了改制射钉枪的致伤力。  相似文献   

液压叠加式力标准机力值重复性、示值误差和长期稳定性观测与思考     

植宇辉  莫先怡  钟泽光 《大众科技》2015,(1):73-74,78

文章以500k N液压方式叠加机作为验证机和研究平台,根据其力值重复性、示值误差和长期稳定性指标优于0.0086%(突破规程0.03级的极限,挑战现有理论模式)的检测数据,评估其不确定度,指出现检定规程存在的问题,坚持以0.01%精度为深入研究的切入点,寻找减小不确定度分量的方法,提出完善高精度叠加机计量传递链的部分改进思路。  相似文献