女子羽毛球运动员后场击球后不同场区单脚落地的生物力学差异——基于三维加速度计的分析

为了探寻女子羽毛球运动员后场击球后单脚落地对膝关节前十字韧带损伤的影响,通过比较正手、反手场区头顶击球单脚落地时躯干加速度及运动变量的差异,寻求运动风险的变量因素。10名优秀女子羽毛球运动员穿戴三维加速计进行单打比赛,使用同步摄像机记录产生超过4g加速度的时刻,分析了加速度>4g时着陆点躯干倾斜角和髋关节外展角。结果显示:在头顶击球过程中,正手场区和反手场区的躯干侧弯及躯干加速度存在差异,反手区头顶击球时横向加速度大于正手区(P<0.05,es=0.706);反手场区单脚落地时躯干倾斜角(24°±7°)大于正手侧(17°±13°);正反手两侧躯干倾斜角均大于先前报道的受伤角度,反手侧的髋外展角(23°±11°)大于正手侧的髋外展角(-1°±8°);反手场区的3个轴的加速度与躯干侧弯、髋外展角度均呈显著相关性。反手场区头顶击球后,单脚落地姿势与前交叉韧带损伤的落地姿势相似,反手侧躯干过度侧弯和高风险落地姿势可能与羽毛球比赛中膝关节前十字韧带损伤有关。     

Knee joint coordination during single-leg landing in different directions

ABSTRACT

Knee joint coordination during jump landing in different directions is an important consideration for injury prevention. The aim of the current study was to investigate knee and hip kinematics on the non-dominant and dominant limbs during landing. A total of 19 female volleyball athletes performed single-leg jump-landing tests in four directions; forward (0°), diagonal (30° and 60°) and lateral (90°) directions. Kinematic and ground reaction force data were collected using a 10-camera Vicon system and an AMTI force plate. Knee and hip joint angles, and knee angular velocities were calculated using a lower extremity model in Visual3D. A two factor repeated measures ANOVA was performed to explore limb dominance and jump direction. Significant differences were seen between the jump directions for; angular velocity at initial contact (p < 0.001), angular velocity at peak vertical ground reaction force (p < 0.001), and knee flexion excursion (p = 0.016). Knee coordination was observed to be poorer in the early phase of velocity-angle plot during landing in lateral direction compared to forward and diagonal directions. The non-dominant limb seemed to have better coordination than the dominant limb during multi-direction jump landing. Therefore, dominant limbs appear to be at a higher injury risk than non-dominant limbs.     

飞机下降和进近中的安全管理

统计资料表明,在造成飞机进近和着陆阶段飞行事故的主要原因中,人为因素占有很大的比重。本文对飞机在下降和进近过程中出现事故的诱因进行了总体分析,经过分步确定目标,核实每一个有疑问的数据,监控每一段飞行中的关键数据,适时调整所需的各项参数,果断地做出正确的决策,进而形成了下降和进近过程中能够确保飞行安全又较为合理的的飞行管理方法。     

跑的支撑时期着地缓冲与后蹬阶段的止、起点划分之我见

中国主要田径教材关于跑的周期阶段的划分存在着多种理论,其中对支撑时期着地缓冲与后蹬起、止点的划分也存在较大分歧。为解决该问题,运用信息技术为主的方法,对世界男子100m纪录保持者博尔特的有关技术参数进行分析。提出了着地缓冲与后蹬止、起点的新划分方法,指出划分应具体量化,以期为短跑技术分析的实际运用提供理论依据。     

舰载直升飞机纵向着舰控制导引研究

在简要分析了舰载直升飞机着舰过程主要特点的基础上,针对着舰过程中的飞行控制问题,提出了基于LQG/LTR方法的控制系统设计。该方法设计的控制系统具有良好的鲁棒性,仿真结果显示了LQG/LTR方法的优越性。     

腾空摆莲转体720°接马步动作的落地稳定性分析

文章运用文献资料法、专家访问法、数理统计法、对比分析法、运动生物力学测试法对腾空摆莲转体720度接马步动作的落地稳定性进行分析研究,认为：落地时刻的躯干角大小、腰骶连接点距离地面的高度、腰骶连接点对X轴的水平速度是影响落地稳定性的主要因素;落地时刻躯干角大、腰骶连接点距离地面高、对X轴水平速度小有利于落地稳定性。     

A dynamic approximation of balanced gymnastics landings

A gymnast can balance after an uneven parallel bar dismount by contacting the ground with an appropriate body position and angular velocity. Balanceable gymnastics landings were predicted by dividing landing into two parts: a short duration impact phase when foot-mat contact forces are high, and a subsequent longer balancing phase during which the gymnast exerts active control at the joints to attenuate the resulting post-impact velocities and achieve a desired motionless terminal configuration. This paper identifies controllable sets of pre-impact landing positions and velocities for a typical female collegiate gymnast that are feasible targets for the end of flight following a single- and double-backward somersault uneven bar dismount with forward mass centre (CM) velocity. Simple algebraic impulse-momentum models for the impact phase determine impulses necessary to stop the feet and slow angular velocity. After impact, a dynamic analysis is needed to determine stability because non-negligible post-impact angular and linear velocities are possible. For almost all successfully balanced landings, ground contact occurs with the CM positioned above the feet and between the toe and heel, because the linear impact impulses that stop the feet also contribute to an angular impulse that slows angular momentum. Only at the largest pre-impact angular velocities following a double-somersault dismount can contact occur with the CM in front of the toe. The gymnast is in balanceable preimpact orientations longer when rotating more slowly and with a smaller angular momentum; therefore balance may be more likely after performing a single-somersault dismount with a large moment of inertia.     

简论都市报报网互动的落地及拓展

近年来,报网互动已经成为新闻媒体发展的主流动作,基于不同模式的报网互动要拓展报媒渠道,实现版面的策划与活动的落地,必须注重传播学理论中的议程设置以及实践中的品牌打造。传媒环境中的都市报报网互动既要规避一定的风险,更要着眼于广阔的前景。     

地表面倾斜度与踝关节护具对垂直着地运动中地面反作用力、踝关节运动学和动力学的效应

研究背景：现有研究文献尚无有关在着地过程中不同表面倾斜度和踝关节护具效应的运动学、动力学和地面反作用力的综合数据。通过对比25°斜面和平面的着地以及使用和不使用踝关节护具情况下来检测踝关节的生物力学特性。研究方法： 11名健康受试者[年龄：（24.6±3.5）岁,身高：（24.6±0.10）m,质量：（65.6±14.9）kg）参与本次研究。受试者在4个动态运动条件下各进行5五次实验：从0.45米高处垂直下落至25°的斜面（IS）或平面（FS）上,使用或不使用半刚性踝关节护具,同时采集三维运动学和测力台地面反作用力数据。利用2×2(表面X踝关节护具)的重复测量方差分析来评估选定的变量。研究结果：与平面着地相比,斜面着地造成较小的垂直和内侧地面反作用力峰值。研究还发现踝关节背曲运动范围、着地角度和背曲速度、最大外翻与跖曲角速度提高,但产生了更大内翻角度和运动范围、着地内翻速度和最大跖曲力矩。踝关节护具在斜面着地时减少了达到地面反作用力第二垂直峰值的时间、着地角度、背曲速度、最大外翻和跖曲速度,但增加了跖曲力矩的最大值。研究结论：斜面增加踝关节额状面的运动范围和踝关节负荷。但是,就斜面着地而言,踝关节护具对踝关节额状面的运动范围和踝关节负荷的影响是相当有限的。