Reply to Glazier: “Comment on ‘Influence of shaft length on golf driving performance’”

Abstract

In this study we compared the kinematic features of the throwing motion between young baseball players of different age groups. Forty‐four Japanese baseball players aged 6.1 to 12.3 years who regularly played baseball, including pitchers and position players, had their throwing actions analyzed three‐dimensionally using high speed videography. Of this sample, 26 players aged above 9 years of age were categorized as the senior group, while the remaining 18 were categorized as the junior group. Senior group throwers had greater height and body mass, and produced a greater ball speed than junior group throwers. The throwing arm movement of senior group throwers was similar to that of adult skilled players. However, in the junior group throwers, the shoulder horizontal adduction angle was larger during the arm acceleration phase, and the maximum angular velocities of elbow extension and shoulder internal rotation occurred later than in senior group throwers. These results indicate that players aged above 9 years can acquire a mature throwing arm movement, while players younger than that will use an immature motion. A possible reason why these differences were shown is that the official baseball is relatively heavy for junior group throwers; they would be better advised to use a lighter ball in throwing practice.     

Development of the Overarm Throw: Movement and Ball Velocity Changes by Seventh Grade

Abstract

Children studied longitudinally from kindergarten through second grade were refilmed in seventh grade as they performed 10 trials of the forceful overarm throw. The horizontal ball velocities of the 22 boys and the 17 girls were compared with predictions made when the children were in second grade. The original estimate of an annual rate of change (a “developmental year”) of 5–8 feet/sec/year (1.52–2.44m) remained accurate for the boys; the original estimate for the girls had to be increased to 2–4.5 feet/sec/year (.61–1.37m). While the gap between the sexes increased throughout elementary school, it increased at a slower rate from second to seventh grade than it had during the primary years. By seventh grade, however, the girls were 5 developmental years behind the boys. The data also suggested a difference in the degree to which the sexes maintained their relative positions within their groups: girls appeared more stable than boys across the elementary years. Change was also assessed in the developmental levels exhibited by the children as they threw. The girls' rate of development was 5–6 years behind the boys' rate. Few boys, however, had reached an advanced level in all movement components by seventh grade. Self-reports suggested that the boys had participated in more overarm throwing than had the girls.     

Qualitative Assessment of the Backswing in Older Adult Throwing

Thirty-six participants performed bilateral and unilateral isometric elbow flexion trials at what they perceived to be 100, 75, 50, and 25% of maximal effort. Absolute bilateral deficits ranged from -16% at 25% effort to -10% at 100% effort. The deficit included a component independent of consciousness and a component inversely related to intensity attributable to perceptual differences between unilateral and bilateral tasks. Forty-two participants performed bilateral and unilateral isometric elbow flexion trials at 100, 80, 60, 40, and 20% of maximal effort. Perception of effort in submaximal bilateral trials was consistently and significantly higher (5.5-9.6%) than corresponding unilateral trials. These data suggest that the bilateral deficit exists at submaximal levels of effort and is based on perceptual and physiological components.     

《摽有梅》新论

《摽有梅》是一首著名的问题诗。如果从生物学的角度对梅子,从文字学的角度对s字,从语法学的角度对＂求我庶士＂等问题进行探讨,这个问题也就迎刃而解了——这是一首表现女子对爱情迫切追求的诗。     

我国优秀女子链球运动员旋转速度的比较研究

速度是掷链球旋转过程中的主要技术指标,也是提高链球运动成绩的关键。运用高速摄影对我国8名优秀女子链球运动员投掷过程中链球速度曲线进行了比较研究,表明运动员在链球旋转中存在着最后一圈速度下降明显,超越器械拉引角不足等关键技术问题。     

对我国掷标枪技术中几个有争议问题的探析

采用文献资料法和专家访谈法,从掷标枪竞技需要和技术的专项竞技性特点,对我国掷标枪技术中3个有争议问题,进行了探析;并提出有效保持投掷过程中身体重心水平速度是判断某些技术环节实效性、合理性的前提。     

上步掷枪--一种简单易学的投掷技术

从目前高校学生身体素质的实际情况出发 ,就投掷标枪中较为关键的环节——投掷步教学进行了阐述 ,并详细探讨了这一环节中的上步掷枪技术的具体步骤。     

江苏省部分优秀女子链球运动员旋转技术的三维运动学分析

采用2台JVC9800高速摄影机，对江苏省3名优秀女子链球运动员的旋转技术进行拍摄和解析，并对旋转阶段的单、双脚支撑时间分布、旋转时间递减率、肩髋角、链球运行斜面等进行运动学分析与比较。     

标枪气动力分析与初始条件的优化组合

标枪是细长的旋成体，投掷成绩受空气动力影响甚大。本课题测定了标枪表面积、转动惯量等基本物理参数，作标枪的受力分析，推导运动方程，求数值解，得标枪出手初始条件的组合模式     

依据运动生物力学原理设计铁饼技术训练手段的研究

尝试将生物力学原理引入铁饼最后用力技术训练中,设计出符合运动特点的手段和方法——橡皮管抽打法。采用实验法对橡皮管抽打法的训练效果进行检验,结果表明：橡皮管抽打法使掷铁饼最后用力技术更趋于科学合理,具有实效性。