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

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.     

影响男子排球运动员扣球起跳动作效果的 动力学研究

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.     

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

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.     

Postural stability,clicker reaction time and bow draw force predict performance in elite recurve archery

Recurve archery is an Olympic sport that requires extreme precision, upper body strength and endurance. The purpose of this research was to quantify how postural stability variables both pre- and post-arrow release, draw force, flight time, arrow length and clicker reaction time, collectively, impacted on the performance or scoring outcomes in elite recurve archery athletes. Thirty-nine elite-level recurve archers (23 male and 16 female; mean age?=?24.7?±?7.3 years) from four different countries volunteered to participate in this study prior to competing at a World Cup event. An AMTI force platform (1000Hz) was used to obtain centre of pressure (COP) measurements 1s prior to arrow release and 0.5s post-arrow release. High-speed footage (200Hz) allowed for calculation of arrow flight time and score. Results identified clicker reaction time, draw force and maximum sway speed as the variables that best predicted shot performance. Specifically, reduced clicker reaction time, greater bow draw force and reduced postural sway speed post-arrow release were predictors of higher scoring shots. It is suggested that future research should focus on investigating shoulder muscle tremors at full draw in relation to clicker reaction time, and the effect of upper body strength interventions (specifically targeting the musculature around the shoulder girdle) on performance in recurve archers.     

振动力量训练对跳远运动员膝关节肌力变化影响的实验

为了拓宽专项力量训练途径,丰富和创新力量训练方法,通过振动力量训练组(II组)和传统力量训练组(I)对比实验研究来探索振动力量训练对跳远运动员下肢肌肉力量训练效果的影响规律,为进一步振动力量训练发展和应用提供实验依据。实验结果表明:振动力量训练法能在同等的负荷条件下,能更有效地发展运动员膝关节屈肌群的最大力量、快速力量、爆发力,其中伸肌表现不明显;振动力量训练也提高了运动员的膝关节肌群力量耐力水平,同时使膝关节屈伸肌群得到协调发展。     

钱塘江排桩式丁坝在涌潮作用下的受力分析

排桩式丁坝是一种新型的水工结构,利用弹性地基梁法和自编的有限元程序计算分析了涌潮作用下的钱塘江排桩式丁坝的内力,研究分析了排桩式丁坝在涌潮作用下的受力机理。前排桩和后排桩的受荷模型不同、刚度不同,导致其桩身内力不同。理论计算和现场测试结果的对比表明,可参考基坑围护工程中的排桩设计理论指导钱塘江排桩式丁坝的设计,并建议采用假定条件较少的有限元法计算分析,使结果更加科学合理,符合实际情况。     

高新技术创业动力的经济学分析

高新技术创业是创业者为了实现其特定的创业目标依托高新技术而开展的一个搜寻和捕获机会并由此创造新颖产品或服务的过程。对创业利益的追求是高新技术创业活动得以进行的基本动力,创业利益的预期值和创业成功的概率决定着创业过程的基本形态和特殊形态,同时获得创业利益的多少也是判断高新技术创业成功与否的重要标准之一。     

合理使用与许可使用的异同及适用

版权法自产生之初,就在对版权是保护还是限制这个问题上陷入两难境地。一方面要鼓励和保护优秀作品的创作与传播;另一方面必须出于对社会公共利益的兼顾而对版权人权利加以限制。总的来看,这种限制主要包括合理使用和许可使用两个方面。     

浅论邓小平对青少年成长的关怀

邓小平同志始终以博大的胸怀和深邃的目光,站在党和国家前途命运的高度,十分关怀青少年的成长。多次向青年发出号召要做“四有”新人,要学习,要参加社会实践,并鼓励大量派遣青少年出国留学,培养了大量的青年专家。     

Impact absorption of tennis shoe-surface combinations

The aim of this study was to investigate, for typical shoes and surfaces used in tennis, the relative role of the shoe and surface in providing cushioning during running. Five test surfaces ranging from concrete to artificial turf were selected, together with two shoe models. Impact absorbing ability was assessed mechanically using drop test procedures and biomechanically using peak magnitude and rate of loading of impact force and peak in-shoe pressure data at the lateral heel. Differences in biomechanical variables between shoe-surface combinations were identified using a two-way ANOVA (p < 0.05). Mechanical test results were found to rank the surfaces in the same order regardless of the shoe model, suggesting that the surface is influential in providing cushioning. However, for all mechanical and biomechanical (p < 0.05) variables representing impact absorbing ability, it was found that the difference between shoes was markedly greater than the differences between surfaces. The peak heel pressure data were found to rank the surfaces in the same order as the mechanical tests, while impact force data were not as sensitive to the changes in surface. Correlations between mechanical and biomechanical impact absorption highlighted the importance of testing the shoe-surface combination in mechanical tests, rather than the surface alone. In conclusion, mechanical testing of the shoe-surface combination was found to provide a strong predictor of the impact absorbing ability during running if pressure data were used. In addition, for typical shoe-surface combinations in tennis, the shoe was found to have more potential than the surface to influence impact loading during running. Finally, in-shoe pressure data were found to be more sensitive than force plate data to changes in material cushioning.