影响男子排球运动员扣球起跳动作效果的 动力学研究          下载免费PDF全文

贾谊 《河北体育学院学报》2017,31(5):64-70

目的:研究男子排球运动员扣球起跳蹬地动作过程中,人体下肢的相关力学参数特征.对象:男子大学生排球运动员10名.方法:使用高速人体动作捕捉系统及三维测力台,对相关运动学和动力学参数进行采集.结果:①起跳过程中,地面反作用力峰值和均值均为优势腿大于非优势腿;②非优势腿地面反作用力峰值与重心最大高度呈高度负相关(r=-0.961,P=0.002＜0.05);③双脚同时着地过程中,优势腿地面反作用力冲量明显大于非优势腿,两脚地面反作用力冲量差与重心最大高度呈显著负相关(r=-0.531,P=0.034＜0.05).结论:①在后排起跳过程中,优势腿与非优势腿表现出不同的用力形式;②应当通过适当控制非优势腿在着地初期的制动作用,并在双脚最后用力阶段有意识地提高非优势腿的参与程度,以提高人体的起跳高度;③排球运动员髌腱炎的发病可能与踝关节绕矢状轴力矩和膝关节绕垂直轴力矩较大有关.  相似文献   

模块化生产网络背景下的劳资关系研究     

陈硕颖 《教学与研究》2011,(5)

模块化生产网络是20世纪80年代以来,跨国公司为了实现弹性生产而组织的全球分工体系。模块化分工促使供应商分化为一级供应商和底层供应商,劳动力分化为核心劳动力和边缘劳动力。劳动力的分化与资本权力的集中造成资强劳弱格局的复辟,从而导致工会力量的衰退和收入差距的扩大。中国在融入全球分工体系的过程中,不可避免地受到全球资强劳弱格局复辟的影响。正确认识这一影响,对于调整国内劳资关系具有重要的意义。  相似文献   

从“文斗”到“武斗”:礼法约束下“斗秧歌”田野调查     

滕希望  郭玉成 《上海体育学院学报》2020,(3):73-83

以海阳大秧歌中的民俗武术活动“斗秧歌”仪式为个案,运用田野调查等方法,从民俗学视角对“斗秧歌”的过程及民俗语境进行分析。认为:海阳大秧歌吸收了军事武术中的兵法谋略与民间武术技术动作,族群生存斗争与比武较技是“斗秧歌”吸收武术元素的重要动因,其逻辑形式表现为礼法约束下由“文斗”到“武斗”的递进,“文斗”体现兵法谋略智慧,武术是“武斗”的主要支撑力量。“斗秧歌”受到礼法约束,以强化乡间社会秩序的稳定,反映了中国传统社会治理中的礼法并施思想。剖析其民俗语境发现,“斗秧歌”是族群生存抗争的仪式手段、护卫生存环境的民间演习、展示个人魅力的艺术舞台,也是地域武术传播的民俗载体。武术与“斗秧歌”之间的融合互动关系,显示武术与民俗活动深厚的历史渊源及武术具有的多元价值属性。  相似文献   

Assessment of leg muscles mechanical capacities: Which jump,loading, and variable type provide the most reliable outcomes?     

Amador García-Ramos  Belén Feriche  Alejandro Pérez-Castilla  Paulino Padial  Slobodan Jaric 《European Journal of Sport Science》2017,17(6):690-698

This study aimed to explore the strength of the force–velocity (F–V) relationship of lower limb muscles and the reliability of its parameters (maximum force [F₀], slope [a], maximum velocity [V₀], and maximum power [P₀]). Twenty-three men were tested in two different jump types (squat and countermovement jump: SJ and CMJ), performed under two different loading conditions (free weight and Smith machine: Free and Smith) with 0, 17, 30, 45, 60, and 75?kg loads. The maximum and averaged values of F and V were obtained for the F–V relationship modelling. All F–V relationships were strong and linear independently whether observed from the averaged across the participants (r?≥?0.98) or individual data (r?=?0.94–0.98), while their parameters were generally highly reliable (F₀ [CV: 4.85%, ICC: 0.87], V₀ [CV: 6.10%, ICC: 0.82], a [CV: 10.5%, ICC: 0.81], and P₀ [CV: 3.5%, ICC: 0.93]). Both the strength of the F–V relationships and the reliability of their parameters were significantly higher for (1) the CMJ over the SJ, (2) the Free over the Smith loading type, and (3) the maximum over the averaged F and V variables. In conclusion, although the F–V relationships obtained from all the jumps tested were linear and generally highly reliable, the less appropriate choice for testing the F–V relationship could be through the averaged F and V data obtained from the SJ performed either in a Free weight or in a Smith machine. Insubstantial differences exist among the other combinations tested.  相似文献   

Kinematic and kinetic analysis of overhand,sidearm and underhand lacrosse shot techniques     

Charles A. J. Macaulay  Pro Stergiou  Darren Stefanyshyn  Luciano Tomaghelli 《Journal of sports sciences》2017,35(23):2350-2356

Lacrosse requires the coordinated performance of many complex skills. One of these skills is shooting on the opponents’ net using one of three techniques: overhand, sidearm or underhand. The purpose of this study was to (i) determine which technique generated the highest ball velocity and greatest shot accuracy and (ii) identify kinematic and kinetic variables that contribute to a high velocity and high accuracy shot. Twelve elite male lacrosse players participated in this study. Kinematic data were sampled at 250 Hz, while two-dimensional force plates collected ground reaction force data (1000 Hz). Statistical analysis showed significantly greater ball velocity for the sidearm technique than overhand (P < 0.001) and underhand (P < 0.001) techniques. No statistical difference was found for shot accuracy (P > 0.05). Kinematic and kinetic variables were not significantly correlated to shot accuracy or velocity across all shot types; however, when analysed independently, the lead foot horizontal impulse showed a negative correlation with underhand ball velocity (P = 0.042). This study identifies the technique with the highest ball velocity, defines kinematic and kinetic predictors related to ball velocity and provides information to coaches and athletes concerned with improving lacrosse shot performance.  相似文献   

基于“问题-用户”的网络问答社区专家发现方法研究     

龚凯乐  成颖 《图书情报工作》2016,60(24):115-121

[目的/意义] 以网络问答社区为研究对象,提出基于“问题-用户”传播网络的专家发现方法,为建立用户激励机制、完善专家推荐方法提供借鉴。[方法/过程] 通过分析开放问答模式的特点,以“问题”和“用户”为节点、“答题关系”为有向边,构建“问题-用户”权威值传播网络,利用答案质量改进加权的HITS算法。[结果/结论] 提出的算法可以较好地兼顾用户的答题数量与答案质量,能够选择出活跃度高、知识渊博的用户作为专家。  相似文献   

质点组内力的功改变质心动能的条件     

田志川 《通化师范学院学报》2003,24(6):25-26

讨论了质点组内力的功是可以改变质心动能的，以及所满足的条件．  相似文献   

Comparison of impact forces,accelerations and ankle range of motion in surfing-related landing tasks     

Lina E. Lundgren  Tai T. Tran  Sophia Nimphius  Ellen Raymond  Josh L. Secomb  Oliver R.L. Farley 《Journal of sports sciences》2016,34(11):1051-1057

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Remote effects of lower limb stretching: preliminary evidence for myofascial connectivity?     

Jan Wilke  Daniel Niederer  Lutz Vogt  Winfried Banzer 《Journal of sports sciences》2016,34(22):2145-2148

The skeletal muscles and the fibrous connective tissue form an extensive, body-wide network of myofascial chains. As fascia can modify its stiffness, strain transmission along these meridians is supposable. The goal of this trial therefore was to collect pilot data for potential remote effects of lower limb stretching on cervical range of motion (ROM). Twenty-six healthy participants (30 ± 6 years) were included in the matched-pairs intervention study. One group (n = 13) performed three 30 s bouts of static stretching for the gastrocnemius and the hamstrings, respectively. An age- and sex-matched control group (CG; n = 13) remained inactive. Pre- and post-intervention, maximal cervical ROM in flexion/extension was assessed. A repeated measures ANOVA revealed systematic differences between groups (P < .05). ROM increased following stretching (143.3 ± 13.9 to 148.2 ± 14°; P < .05) but remained unchanged in the CG (144.6 ± 16.8 to 143.3 ± 16.8°; P > .05). Our data point towards existence of a strain transfer along myofascial meridians. Further randomised controlled studies on conditions, factors and magnitude of tensile transmission are warranted.  相似文献   

卢瑟福模型中电子运动分析     

秦希峰  刘增良 《临沂师范学院学报》2007,29(3):24-26

关于卢瑟福模型中电子的运动是加速还是减速,不同文献给出不同描述,甚至是截然相反的描述.本文分别从能量和力的角度定量、定性地分析了卢瑟福模型中电子的运动情况,得出了卢瑟福模型中电子绕原子核旋转、辐射能量时作加速运动的结论.  相似文献