Somersaulting techniques used in high-scoring and low-scoring Roche vaults performed by male Olympic gymnasts

Abstract

The aim of this study was to compare the somersaulting techniques used in the 16 highest-scoring and 16 lowest-scoring Roche vaults. Our hypothesis was that the gymnasts performing the highest-scoring Roche vaults would demonstrate a better technique than those performing the lowest-scoring Roche vaults while on the horse (pushing off the horse more effectively), somersaulting (executing most of the required somersaults higher in flight), and landing (showing a greater control). A 16-mm motion picture camera, operating at 100 Hz, recorded the vaults during the official competition. The two-dimensional direct linear transformation was used for spatial reconstruction. The results of t-tests (P < 0.05) indicated that, compared with the low-scoring gymnasts, the high-scoring gymnasts had: (1) greater height of body centre of mass and a more fully extended body position at the horse take-off; (2) greater height of body centre of mass at the peak of post-flight, knee release, and touchdown on the mat; (3) greater horizontal and vertical displacements of body centre of mass, greater somersaulting rotation, and longer time from the knee release to mat touchdown; and (d) markedly smaller landing point deductions. In conclusion, a successful Roche vault is likely when the focus is on: (a) leaving the horse with a large vertical velocity in an extended body position to achieve a high trajectory of centre of mass by first extending the legs, then immediately pushing off the horse vigorously, using the muscles of the upper extremity; (b) grasping the knees immediately after the take-off from the horse, achieving the tightly tucked body position early during the ascent to the peak, and completing two-thirds of the required somersaults at a great height; (c) releasing the knees and extending the body above the top level of the horse; and (d) contacting the mat with a high body centre of mass position.     

Correlation of axial impact forces with knee joint forces and kinematics during simulated ski-landing

Abstract

Anterior cruciate ligament (ACL) rupture, during ski-landing, is caused by excessive knee joint forces and kinematics, like anterior tibial translation, internal tibial rotation, and valgus rotation. It is not well understood how these forces/kinematics are directly related to ski-landing impact. In the present study, we applied simulated ski-landing impact to knee specimens, and examined joint force/kinematic responses and their correlations with impact force. Ten human cadaveric knees were subjected to axial impact loading at 70° of flexion to simulate ski-landing impact. Impact was repeated with incremental magnitude until ACL failure. Axial impact forces, anterior-posterior and medial-lateral tibial forces were measured using a tri-axial load cell. Anterior-posterior tibial translation, internal-external tibial rotation, and valgus-varus rotation were determined using a motion-capture system. We found positive correlations of axial impact force with anterior tibial force, medial tibial force, anterior tibial translation, internal tibial rotation, and valgus joint rotation. Axial impact forces were more strongly correlated with anterior tibial forces (R ² = 0.937 ± 0.050), anterior tibial translation (R ² = 0.916 ± 0.059), and internal tibial rotation (R ² = 0.831 ± 0.141) than medial tibial force (R ² = 0.677 ± 0.193) and valgus joint rotation (R ² = 0.630+0.271). During ski-landing, these joint forces/kinematics can synergistically act to increase ACL injury risk, whereby the failure mechanism would be dominated by anterior tibial forces, anterior tibial translation, and internal tibial rotation.     

Effects of two football stud configurations on biomechanical characteristics of single-leg landing and cutting movements on infilled synthetic turf

Multiple playing surfaces and footwear used in American football warrant a better understanding of relationship between different combinations of turf and footwear. The purpose of this study was to examine effects of shoe and stud types on ground reaction force (GRF) and ankle and knee kinematics of a 180° cut and a single-leg 90° land-cut on synthetic turf. Fourteen recreational football players performed five trials of the 180° cut and 90° land-cut in three shoe conditions: non-studded running shoe, and football shoe with natural and synthetic turf studs. Variables were analyzed with a 3 × 2 (shoe × movement) repeated measures analysis of variance (p < 0.05). Peak vertical GRF (p < 0.001) and loading rate (p < 0.001) were greater during 90° land-cut than 180° cut. For 180° cut, natural turf studs produced smaller peak medial GRFs compared to synthetic turf studs and non-studded shoe (p = 0.012). For land-cut, peak eversion velocity was reduced in running shoes compared to natural (p = 0.016) and synthetic (p = 0.002) turf studs. The 90° land-cut movement resulted in greater peak vertical GRF and loading rate compared to the 180° cut. Overall, increased GRFs in the 90° land-cut movement may increase the chance of injury.     

大型民用水陆两栖飞机降落构型告警的研究

根据中国民用航空规章的要求以及水陆两栖飞机的降落告警需求,文章对大型民用水陆两栖飞机陆上及水上降落构型进行研究。     

浅析模拟训练法在渡海登岛400m障碍教学中的运用

渡海登岛400m障碍是以渡海登岛作战需求为牵引,为提高部队“打赢”能力而设置的一项军事训练课目。采用模拟训练法进行训练,是训练与实战相结合的军事训练模式,也是这一课目今后训练的主要模式。通过这种模拟实战的训练方式,使受训者的体能素质、心理素质、战场适应能力得到全面提高,练就过硬军事技能,增强实战能力。     

论通货紧缩对我国经济的影响

通货紧缩对经济的破坏力度与通货膨胀相比是一样的，甚至有过之而无不及。首先，通货紧缩会加速经济的衰退。由于物价的持续下跌，必然导致人们对经济前景的悲观预期，持币观望，使消费或投资进一步萎缩。其次，物价的下跌还会提高实际利率．加重债务人的负担．即名义利率下降，资金成本仍然比较高。致使企业不敢贷款投资，或难以偿债。银行则出现大量坏帐．并难以找到盈利的项目提供贷款，经营效益不断滑坡，造成国际收支逆差扩大和资本外流。     

对短跑途中跑技术动作若干理论问题的探讨--兼与董广新、王喆夫两作者商榷

运用运动生物力学的基本原理，结合田径运动理论知识，对短跑的动作周期划分为“后瞪”、“着地缓冲”等问题进行了剖析。我们认为在着地缓冲阶段，脚着地点的远近取决于运动员身体形态、身体素质和技术水平，脚着地时的冲量对维持身体平衡作用不大。运动员在后蹬阶段“屈蹬式”技术是伴随塑胶跑道的出现而产生的一种特有现象。无论“以蹬带摆”或“以摆促蹬”，都应强调蹬摆的协同作用，而不能强调某一方面而忽视另一方面。     

自由式滑雪空中技巧运动员落地稳定性主要影响因素的研究

对自由式滑雪空中技巧运动员落地稳定性问题建立了四个运动环节的人体运动模型。雪板雪靴、足、小腿定义为环节1,大腿定义为环节2,躯干、头定义为环节3,上臂、前臂、手定义为环节4。根据平动动坐标系下相对动量矩定理建立了描述自由式滑雪空中技巧运动员落地稳定性控制人体对人体质心动量矩的模型。模型是有效的,并能反应落地稳定性控制的内在主要影响因素。     

铅球、铁饼落地区的一种画法和计算

改进正切量法的测量和画法,不用画纵轴线和垂直纵轴的直线,只用三步测量定点就可以确定落地区两条角度线的点,从而减小了正切量法的操作步骤和实际丈量的难度,提高了画铅球、铁饼、链球投掷场地的工作效率.     

我国优秀女子蹦床运动员网上空翻类动作水平移动过大的运动学分析

选取了4名优秀女子国家队队员做为研究对象,主要运用摄像法和三维录像解析法对我国蹦床运动员网上普遍存在的非技术性位移问题,即水平移动过大问题进行了研究.研究结果表明:1)非技术性位移主要表现在纵向水平移动上,向前类和向后类空翻动作在纵向水平移动上不存在显著差异.2)在纵向水平上产生非技术性位移的向前类和向后类空翻动作离网瞬时重心的水平速度在1.00m/s以上,腾起角在80°以下.3)非技术性位移与前一个动作形成的不良的入网时空参数有关,前一个动作入网时重心水平速度在1.00m/s以上,入网角在80°以下就会对下一个动作的起跳产生影响.