On using wearable tri-axial accelerometers to examine the striking phase kinematics of expert specialist drag flickers on-field

Analysing player kinematics during a match using “gold-standard” 3D video-based motion analysis techniques is a difficult prospect indeed. The development of small, wireless, wearable sensors offers the potential to reduce the challenges of measuring kinematics during match-play without hindering performance. The present study examined the viability of using wireless tri-axial accelerometers to examine whether key performance measures of drag flicks executed by expert specialist drag-flickers are predicted by the kinematics of the striking phase. Linear mixed models were used to examine whether the speed and accuracy of players’ drag flicks were predicted by the duration of stick-ball contact, and the kinematics of the lead lower limb at stick-ball contact and ball release. Results revealed that stick and lead lower limb kinematics significantly predicted shot accuracy but not shot speed. Shorter drag-time predicted more accurate flicks (p = 0.03) as did a more vertical leg at stick-ball contact (p = 0.016) and a more horizontal thigh at ball release (p = 0.001). This may indicate that there are more ways to produce fast drag flicks than accurate ones. This study illustrates that wireless tri-axial accelerometers can be used on-field to measure the effects of kinematics on key performance measures.     

Low fundamental movement skill proficiency is associated with high BMI and body fatness in girls but not boys aged 6–11 years old

This study examined differences in children’s body mass index (BMI) and body fatness (BF%) as a function of gender and fundamental movement skill (FMS) proficiency. Following ethics approval and parental consent, 248, 6–11 year-old children (112 boys, 136 girls) underwent assessment of 7 FMS: sprint run, side gallop, hop, kick, catch, throw and vertical jump. FMS tertiles (“high”, “medium” or “low” FMS) were created based on the summed components of the FMS. Skinfold measures were used to calculate BF%. Physical activity (PA) was assessed using pedometry and maturation predicted using anthropometry. Data were analysed using a 2 (Gender) × 3 (FMS tertile) ways analysis of covariance (ANCOVA), controlling for age, maturation and PA. Age (P = .001) and maturation (P = .006) were associated with BMI. Girls classified as high FMS proficiency had significantly lower BMI compared to girls with low and medium FMS proficiency. Age (P = .0001) and maturation (P = .007) were associated with BF%. BF% was also higher for girls with low FMS compared to those with medium and high FMS. BF% and BMI were not different across FMS tertile in boys. Such findings suggest focusing on FMS may be especially important for healthy weight, particularly in girls.     

Modelling coaching practice: the role of instruction and demonstration

In this paper, we review the empirical literature pertaining to the effectiveness of instructions and movement demonstrations. Initially, we examine existing theories and approaches that try to explain the process of skill acquisition so as to determine implications of these theories for instructional provision. This is followed by an evaluation of studies in the motor learning literature in which pre-practice information has been manipulated. Explicit learning strategies are contrasted to implicit and discovery learning methods, and current explanations for instructional effects are discussed in terms of such mechanisms as effects-related attentional focus and movement variability. In the final sections, we review data from our own laboratory where pre-practice information has been manipulated during the learning of a novel bimanual coordination task. From these studies, proposals are made to try and explain how pre-practice information works to effect the process of skill acquisition, including the selection and execution of a response and the processing of associated feedback. An important role is given to the existing skills of the learner in understanding the instructions and performing the desired movement. Finally, we suggest some practical implications of this empirical evidence for the teaching of motor skills.     

Gentile运动技能分类法应用于羽毛球教学的实验研究

根据金特尔（Gentile）二维分类法,对羽毛球正手高远球技能操作从环境背景和动作功能两个维度进行分类,并将其运用到教学实验中,该实验采用自身比较法和组间对比法。教学结果表明：实验组羽毛球正手高远球技术得到明显提高,其技术动作规范程度优于对照组。通过对两组同学羽毛球正手高锭球技术的综合测试,实验前后两组同学的考核结果呈...     

双馈电机双三电平调速系统的研究

本文在简化三电平空间矢量脉宽调制算法的基础上,以双馈电机为控制对象,重点研究了其在定子磁链定向下的控制技术;主电路采用双三电平背靠背拓扑结构,分别论述了其中前端整流器与末端逆变器的控制方法,并通过仿真进行了验证;搭建了一套实验平台,给出了器件选型方法,同时对系统软、硬件结构进行了详细描述,最后通过实验证明了文中所提控制策略与软、硬件的设计都是正确、有效的。     

直流电机的基本工作原理与结构教学方法探讨

围绕直流电机的基本工作原理与结构这节课的重点和难点,结合教学实践,从导语设计、激疑教学、多媒体教学、教材内容处理等4个方面对其教学方法进行了讨论,以期对教学同行提供借鉴.     

Natural nano-machines

In the first part of this article, we read about Alice’s guided tour through the cellular microfactory. In the second part, I introduce the methods of studying the materials and mechanisms of the molecular machines through dialogues. The three participants in this discussion are Alice, her elder brother Alex and her father Albert. The style of presentation here is adapted from Galileo’s Dialogue Concerning the Two Chief World Systems. Albert, a professor of biophysics, emphasizes the crucial differences between the mechanisms of the natural nano-machines and those of their macroscopic counterparts. He also points out some practical applications of this interdisciplinary research in biomedical science and nano-technology. Debashish Chowdhury is a professor of Physics at IIT Kanpur. He is a theoretical physicist and the areas of his research interest are statistical and biological physics. He plays with toy models using mathematical formulae and simulates nature with computers.     

三相异步电动机的不对称运行

利用对称分量法对三相异步电动机不对称运行状态下电磁关系进行了分析，阐述了 不对称运行状态对电机性能的影响。     

人机界面与PLC在物料分拣系统中的应用

人机界面和PLC在工业控制中得到了广泛的应用,本文简要介绍将信捷TP系列TP460-T型触摸屏与三菱FX2N型PLC相结合,应用于物料分拣系统中。通过PLC及人机界面与机械手的通信,可在人机界面上直接控制机械手动作,实现现场控制的一种全新的图形操作界面,为人机友好交互提供有效和便捷的途径,大大简化操作过程,提高工作效率,降低生产成本。     

从运动技能学习的“高原现象”看我国地市级体校训练管理的弊端

多数地市级体校把向上级体校或专业运动队输送运动员,在各级竞技比赛中夺取奖牌的数量作为教练员的责任目标,并把完成目标的结果与教练员的福利、待遇挂钩。而这个年龄段的青少年运动员,在校期间大多处于运动技能学习中的“高原现象”期,运动技能提高缓慢,甚至停滞、下降。教练员为了完成其责任目标,往往采取“揠苗助长”式的训练方法,进行大运动量、高强度超负荷的训练,或使用不合理的营养补剂,违犯了运动训练的科学规律,影响了青少年运动员的身心健康;也使不少未突破“高原现象”期而具有良好运动潜力的青少年运动员被淘汰,造成人、财、物的浪费。最后提出了改变这一局面的建议