散打鞭腿动作技术的二环节链模型的运动学分析

鞭腿动作是散打腿法技术的核心,将散打鞭腿动作简化为一个二环节运动链模型,对散打鞭腿动作的髋、膝关节和大腿、小腿环节在三维平面内进行位置矢量的确定,以此确定在鞭腿动作中,各关节和环节的运动学参数,然后确定目标函数(末端速度V),建立了人体鞭腿动作的三维运动学方程,将鞭腿动作各环节要领数学化描述,结论认为:(1)鞭腿动作中大腿的角速度由腰部角速度和髋关节角速度决定,小腿的角速度由大腿和膝关节的角速度决定,三者密切配合共同决定着鞭腿末端的速度;(2)在T1阶,大小腿下潜完曲度不易超过450,在进攻腿离地瞬间,小腿环节的角速度大于大腿环节的角速度时最有利于膝关节速度的增加,进攻退离地时膝关节的角速度主要由小腿蹬地时的地面反作用力决定;(3)在T2阶段,大小腿充分折叠有利于膝关节角速度的加大;(4)人体的鞭腿环节链模型中,鞭打原理遵从动量由近端环节向远端环节传递的原理,通过髋关节及时有效的制动可使膝关节动量增加,通过膝关节的制动可使动量传递到末端,引起末端加速。(5)在散打鞭腿环节链模型中只有多环节和关节依次协调配合才能使末端发挥最佳击打效果。     

Influence of hamstring extensibility on sagittal spinal curvatures and pelvic tilt in highly trained young kayakers

Abstract

Objective: To evaluate the influence of hamstring extensibility on spinal and pelvic postures adopted by young paddlers in their kayaks.

Methods: Sixty-eight young elite kayakers were recruited for the study (mean value 15.23, s=0.68 years). Thoracic and lumbar curvatures and pelvic position were evaluated with a Spinal Mouse system in standing position and in the boat (seated in the kayak with the paddle resting on their thighs, right entry position and left entry position). Hamstring muscle extensibility was determined in both legs by passive straight leg raise test (PSLR). The sample was divided into two groups with regard to straight leg raise angle (Group A, PSLR < 80°, n=32, and group B, PSLR ≥ 80°, n=32).

Results: Paddlers with lower extensibility presented higher thoracic and lumbar flexion and a more posterior pelvic tilt in the kayak in all three positions. However, no significant differences were found between the groups when standing.

Conclusion: The results suggest that lower hamstring extensibility is related to increased spinal flexion and posterior pelvic tilt, which can overload the spine during paddling training. A systematic and intensive stretching programme to improve hamstring muscle extensibility should be incorporated into the training activities of paddlers.     

Pygmalion in the Gym: A Model for the Communication of Teacher Expectations in Physical Education

Abstract

Much research on teacher expectations has focused on ways in which teacher perceptions of student ability can ultimately affect student performance. The majority of this research has indicated that teacher expectations not only determine certain types of student performance, but also serve to sustain low and high levels of performance. Observational research has also demonstrated that differential teacher-student interactions are related to certain levels of teacher expectations. For example, it has been shown that high expectancy students receive more praise, acceptance of ideas, contact and wait time, and more response opportunities than low expectancy students. Much of this research has been generated from studies related to classroom instruction. Very little of this research, however, has been operational in the physical education setting. One reason for this is the absence of a model in physical education through which this type of research can be generated. This article presents such a model showing how expectations are formed, how they are communicated, and how they sustain low and high levels of student growth and performance. The model further illustrates the causal relationship among teacher expectations, dyadic interactions and student growth and performance. Suggestions for future research techniques to determine causal flow among variables are also presented.     

Squat Jump Performance During Growth in Both Sexes

The purpose of this cross-sectional study was to investigate leg muscle power and compare two activities (jumping and cycling) in 383 girls and 407 boys ages 9–19 years. Results in anthropometric characteristics and jumping performance were comparable until midadolescence, and sex differences were observed. Lean leg volume (LLV) was the reason for most of the variance (76% in girls and 88% in boys) in jumping performance. However, the LLV exponent was higher than expected in boys but not girls. Therefore, unidentified qualitative changes of muscle function during growth in boys must be considered. The squat jump index (SJI) was highly correlated to cycling peak power (CPP; N = 790, r = .94, p < .001). Although prediction error of CPP from SJI was less than 5% when considering each sex-and-age group, individual errors mounted to 40%. Due to its practicability, SJI is recommended in large-scale developmental prospective studies. However, cycling and jumping protocols are not interchangeable when measuring peak power values.     

关于短跑后蹬角度若干问题的探讨

后蹬力是短跑主要的动力来源，是推动人体前进的基本条件。决定跑速的主要因素是步长与步频。然而后蹬角度的大小，对后蹬力的利用率，对步长与步频都将产生影响。后蹬角度大，对后蹬力的利用率、对步长与步频都会起消极的作用。本文主要对如何减小后蹬角度，以利于改进短跑技术，提高短跑运动成绩作一些探讨。     

竞技武术套路中搬脚朝天蹬直立平衡动作下肢肌肉用力特征的表面肌电分析

运用表面肌电遥测和高速摄影同步测试技术,对竞技武术套路中搬脚朝天蹬直立平衡动作的下肢肌 肉用力特征进行测试。结果显示： 所测五名女子运动员的下肢六部位肌肉（胫骨前肌、臀中肌、臀大肌 、腓肠肌、股二头肌和股直肌）的放电大小顺序和先后顺序相似,即胫骨前肌最先放电且放电量最大、其 次是臀中肌和臀大肌几乎同时放电,而后依次是腓肠肌、股二头肌和股直肌。在完成动作过程中,运动员 的运动级别越高,其各部位肌肉的总积分肌电值却越低。武英级运动员与二级运动员在股直肌、股二头肌 、胫骨前肌、臀中肌上的均方根振幅(RMS)指标上存在显著性差异（P<0.05）。与二级运动员相比,武英 级运动员在完成该动作时肌肉间的配合更协调,总体更省力。     

轮滑双蹬技术外刃蹬地动作的加速度情况分析

探究轮滑运动双蹬技术的外刃蹬地动作是否在前进方向产生了加速度,运用数理演绎方法进行分析。结果：外刃蹬地动作在水平方向上只能产生一个不大的侧向力,当右脚外刃蹬地动作的滑行轨迹处于以运动员总运动方向为Y轴的直角坐标系的第Ⅱ象限、或左脚外刃蹬地动作的滑行轨迹处于同一直角坐标系第1象限时这个侧向力指向运动员总运动方向的侧后方,产生的加速度与总运动方向呈负值。结论：双蹬技术外刃蹬地动作在水平方向上只能产生一个不大的与总运动方向相反的加速度。     

对跳远起跳过程中摆动腿作用的研究

采用文献资料法，数理统计法，比较分析法，从缓冲和蹬伸阶段对跳远起跳过程中摆动腿作用进行研究。结果表明摆动腿的正确摆动过程和有效用力方法对达到理想化腾起初速度和腾起角起着关键作用，在缓冲阶段，摆动腿的摆动对重心的垂直速度起着主导作用，摆动腿摆腿速度越快，可为后继的蹬伸动作创造更好的条件。起跳蹬伸阶段摆动腿的摆动制动加速度直接影响起跳离地瞬间起跳的蹬伸运动效果，与腾起初速度和跳远成绩有着密切的联系。     

不同投掷项目最后用力阶段右腿技术特征的比较分析

运用三维运动解析系统,对我国部份男子铅球、标枪、铁饼运动员最后用力过程中右腿技术特征进行了运动学的比较分析,结果表明三个项目最后用力过程中右腿工作方式存在着较大的差异.     

从膝角看不同水平男子跳远运动员摆动腿技术

主要从运动学的角度出发,着重从摆动腿膝关节角度的变化特点来分析不同水平男子跳远运动员起跳过程中摆动腿技术的异同,高水平运动员,在最后一步摆动腿蹬离地面瞬间,表现出相对较小的摆动腿膝关节角,角度变化曲线上表现为角度峰值出现在离地后0.02~0.03秒左右的瞬间,不同水平男子跳远运动员在起跳腿着地、起跳腿膝最大屈、起跳离地3个特征时刻,摆动腿膝关节角度差异不明显。