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31.
1 Ｉｎｔｒｏｄｕｃｔｉｏｎ Ｉｔｉｓｗｅｌｌｋｎｏｗｎｔｈａｔｍｅｔａｌｈｙｄｒｉｄｅｓａｒｅａｎｉｄｅａｌｍｅｄｉｕｍｆｏｒｈｙｄｒｏｇｅｎｓｔｏｒａｇｅｄｕｅｔｏｔｈｅｉｒｈｉｇｈｄｅｎｓｉｔｙａｎｄｈｉｇｈ ｐｕｒｉｔｙｏｆｈｙｄｒｏｇｅｎ .Ｈｏｗｅｖｅｒ ,ａｌｌｋｎｏｗｎｃｏｎｖｅｎｔｉｏｎａｌｍｅｔａｌｈｙｄｒｉｄｅｓ ,ｉｎｃｌｕｄｉｎｇｉｎｔｅｒｍｅｔａｌｌｉｃｃｏｍｐｏｕｎｄｓＡＢ5,ＡＢ2 ,ａｎｄＡＢ ,ｈａｖｅｒｅｖｅｒｓｉｂｌｅｇｒａｖｉ ｍｅｔｒｉｃＨ ｄｅｎｓｉｔｉｅｓｎｏｍｏ… 相似文献
32.
王永祥 《衡阳师范学院学报》2002,23(6):137-139
针对高等学校《电路分析》中“正弦稳态电路的分析”这一教学重点,难点,在教学中正确引入“相量”的概念,简化正弦稳态电路分析过程中繁杂的数学运算;通过归纳,对比,总结,达到由浅入深,循序渐进的教学目的。 相似文献
33.
目的：探索跆拳道运动员前横踢动作下肢优势侧和非优势侧的运动生物力学特征差异性。方法：采用Vicon三维运动捕捉系统、Kistler三维测力台和Deado电子护具计分系统,采集13名跆拳道运动员前横踢动作下有效得分时髋、膝、踝关节的运动学和动力学数据,使用Visual3D软件对采集数据进行逆向运动学和动力学计算,并对结果采用配对样本T检验的方法进行差异性分析。结果：(1)进攻腿：髋关节屈曲力矩峰值、膝关节伸展力矩峰值优势侧大于非优势侧(p<0.05),膝关节屈曲最大角度优势侧大于非优势侧(p<0.01),髋关节伸展力矩峰值、外展最大角度非优势侧大于优势侧(p<0.01)。(2)支撑腿：髋关节屈曲幅度、屈曲功率峰值、外展功率峰值优势侧大于非优势侧(p<0.05),髋关节外展力矩峰值、膝关节伸展力矩峰值优势侧大于非优势侧(p<0.01),髋关节伸展角速度峰值、踝关节跖屈力矩峰值非优势侧大于优势侧(p<0.05),髋关节外展角速度峰值、膝关节屈曲力矩峰值、踝关节旋外角速度峰值非优势侧大于优势侧(p<0.01)。(3)进攻腿击打力度值及进攻腿和支撑腿垂直... 相似文献
34.
Chris Pocock Neil E. Bezodis Keith Davids Jamie S. North 《European Journal of Sport Science》2018,18(10):1309-1316
Place kicks in Rugby Union present valuable opportunities to score points outside the spatiotemporal dynamics of open play but are executed under varying performance constraints. We analysed effects of specific task constraints and relevant contextual factors on place kick performance in the 2015 Rugby Union World Cup. Data were collected from television broadcasts for each place kick. In addition to kick outcomes, contextual factors, including time of the kick in the match, score margin at the time of the kick, and outcome of the kicker’s previous kick, were recorded. Effects of spatial task constraints were analysed for each kick, using distance (m) and angle (°) of the kick to the goalposts. A binomial logistic regression model revealed that distance from, and angle to, the goalposts were significant predictors of place kick outcome. Furthermore, the success percentage of kickers who missed their previous kick was 7% lower than those who scored their previous kick. Place kick success percentage in the 10 minutes before half-time was 8% lower than the mean tournament success percentage, which was 75% (95% CI 71–78%). The highest kick success percentage was recorded when scores were level (83%; 95% CI 72–91%). Our data highlighted how subtle changes in task constraints and contextual factors can influence performance outcomes in elite performers in international competition. Fluctuations in place kick success suggested that individual constraints, such as thoughts, emotions and fatigue, induced during competition, could interact with perceptions to influence emergent performance behaviours. 相似文献
35.
摘要：为提高我国短跑运动技术水平提供理论支持,以第16届亚运会100 m跑男运动员为研究对象,通过对54人次的起跑后蹬时间－压力曲线结构进行对比分析,得出了双波峰与三波峰两种曲线类型。研究结果表明：双波峰结构优势在于双脚后蹬时间短和双脚后蹬力量更大,是一种更为合理的起跑后蹬时间－压力曲线结构。在起跑训练中,我们应重点加强双脚后蹬用力协同性的训练。如果劳义在起跑训练中将其起跑后蹬时间－压力曲线由三波峰结构转变为双波峰结构,将使他的100 m成绩由10.24 s提高到10.21s的水平。 相似文献
36.
Ross H. Sanders 《Journal of sports sciences》2013,31(2):213-227
Abstract The purpose of this study was to establish the characteristics of the movement patterns common to flutter kicking of skilled swimmers and to determine how the movement patterns of swimmers at different levels of a “learn-to-swim” programme differ from those of skilled swimmers. Also, the nature of the skill afforded the opportunity to investigate learning of a cyclical multi-joint task from a motor control perspective. The underwater motion of nine children representing three levels of a “learn-to-swim” programme and 10 skilled swimmers were video-recorded while performing nine cycles of prone flutter kicking. Kinematics including joint angular motion and coordination of joint actions were calculated. Fourier analysis was applied to determine the frequency composition of the vertical undulations of the hip, knee, and ankle and to calculate the velocity of the body wave travelling caudally from hip to ankle. Fourier analysis also enabled investigation of biological noise, as distinct from variability. The results indicated the desired joint angles and coordination towards which learners could be guided. An index based on the ratio of hip – knee and knee – ankle body wave velocities showed that the inter-joint coordination of most learners was not appropriate for effective flutter kicking. There was strong evidence to suggest that skilled performance in flutter kicking is characterized by sequencing of joint actions to produce a single sinusoidal body wave moving caudally with not decreasing and preferably increasing velocity, low biological noise, and small variability. 相似文献
37.
Abstract In freestyle swimming the arm action is routinely quantified by stroke count and rate, yet no method is currently available for quantifying kick. In this study, we assessed the validity and reliability of inertial sensor technology (gyroscope) to assess kick count and rate. Twelve Paralympic swimmers completed a 100-m freestyle-swimming time-trial and freestyle kicking-only time-trial three times each in a season. An algorithm was developed to detect the up and down beat of individual kicks from the gyroscope trace. For comparative purposes, underwater video analysis provided the criterion measure. The standard error of the estimate (validity) for kick count, expressed as a coefficient of variation, was 5.9% (90% confidence interval 5.5 to 6.4) for swimming, and 0.6% (0.5 to 0.6) for kicking-only trials. The mean bias for kick count was ?1.7% (?2.4 to ?1.1) for swimming, and ?0.1% (?0.2 to ?0.1) for kicking-only trials. Correlations between the sensor and video for kick count were 0.96 (0.95 to 0.97) for swimming, and 1.00 (1.00 to 1.00) for kicking-only trials. The typical error of the measurement (reliability) between trials was approximately 4% for kick count and rate. The inertial sensors and associated software used generated sufficient validity and reliability estimates to quantify moderate to large changes in kick count and rate in freestyle swimming. 相似文献
38.
Donghyun Ryu Seonjin Kim Bruce Abernethy David L. Mann 《Research quarterly for exercise and sport》2013,84(2):252-262
Purpose: The ability to anticipate the actions of opponents can be enhanced through perceptual-skill training, though there is doubt regarding the most effective form of doing so. We sought to evaluate whether perceptual-skill learning would be enhanced when supplemented with guiding visual information. Method: Twenty-eight participants without soccer-playing experience were assigned to a guided perceptual-training group (n = 9), an unguided perceptual-training group (n = 10), or a control group (n = 9). The guided perceptual-training group received half of their trials with color cueing that highlighted either the key kinematic changes in the kicker's action or the known visual search strategy of expert goalkeepers. The unguided perceptual-training group undertook an equal number of trials of practice, but all trials were without guidance. The control group undertook no training intervention. All participants completed an anticipation test immediately before and after the 7-day training intervention, as well as a 24-hr retention test. Results: The guided perceptual-training group significantly improved their response accuracy for anticipating the direction of soccer penalty kicks from preintervention to postintervention, whereas no change in performance was evident at posttest for either the unguided perceptual-training group or the control group. The superior performance of the guided perceptual-training group was preserved in the retention test and was confirmed when relative changes in response time were controlled using a covariate analysis. Conclusions: Perceptual training supplemented with guiding information provides a level of improvement in perceptual anticipatory skill that is not seen without guidance. 相似文献
39.
Abstract The influence of the Cardan rotation sequence on the orientation angles for joints is well known but has not been explored for dynamic sports movements. The purpose of this study is to establish the influence of Cardan rotation sequence on the orientation angles of the ankle, knee, and hip of the support leg and pelvis during dynamic sports movements, typified by a maximal instep kick in soccer. We found that: (a) the X (flexion/extension) axis rotations provide data that are robust for any sequence used other than the YXZ sequence, although the Y (abduction/adduction) and Z (internal/external) axes rotations are variable in both shape and offset magnitude; (b) the preferred rotation sequence is either XYZ or XZY for dynamic sports movements, although for the soccer kick the XYZ rotation sequence has been widely used and so this is recommended as a standard; and (c) most uncertainties exist in the Y and Z axes and are most apparent at the beginning of the movement. Where uncertainty exists in identifying Y and Z axes orientations, the integrated angular velocity may be considered as an alternative to determine the relative changes in segment orientation. 相似文献
40.