Motor variability in sports: A non-linear analysis of race walking

Abstract

This aim of this study was to analyse the nature of movement variability and to assess whether entropy measures may represent a valuable synthetic index of neuromuscular organization. The regularity of kinematic/kinetic time series during race walking, the changes in the structure of intra-individual variability over the test session, and the influence of athletic skill in (inter)national rank athletes were investigated. Motion analysis techniques were used. Sample entropy (SampEn) was adopted to examine fluctuations in lower limb angles and ground reaction forces. The regularity of both original and surrogate time series was assessed and compared, by estimating SampEn, to verify the presence of non-linear features in movement variability. SampEn was statistically lower in the original data than in surrogates. In contrast, the regularity of time series did not change significantly throughout the subsequent intra-individual repetitions. Hip and ankle joint angles and vertical ground reaction force manifested increased entropy for skilled athletes. Results suggest that race walking variability was not only the product of random noise but also contained information about the inherent propriety of the neuro-musculo-skeletal system. Furthermore, they provide some indications about neuromuscular control of the lower limb joints during race walking gait, and about the differences between more and less skilled individuals.     

Baumgartner's Modified Pull-Up Test For Male and Female Elementary School Aged Children

Abstract

Nineteen college men and women (aged 18–23 yrs, × = 21.1) were studied to ascertain the force-time components of a rapid maximal voluntary isometric contraction (MVC) for ankle dorsiflexors, knee extensors, elbow flexors, wrist flexors and hand grip. Standardized isometric strength testing protocol was used. After a practice period subjects were instructed to make an MVC without jerking and as quickly as possible, for each of the muscle actions noted above. Force readings were taken from a load cell assembly through an analogue-to-digital converter and analyzed to yield time values for MVC, 3/4 MVC, 1/2 MVC, and 1/4 MVC. The results indicated significant differences (p < .01) between the responses of the men and women, with the women reaching full MVC more rapidly than the men. Also, there were significant differences among the five muscle groups tested, with the wrist flexor muscle group developing MVC most quickly, while the knee extensors took the longest time to full MVC. Based upon these data it may be concluded that the time to full MVC differs between men and women, and also that the time to full MVC differs among the five muscle groups tested in this experiment.     

论时空变化与篮球运动的发展

时间和空间在篮球运动中有着明确的规定,二者的辩证关系广泛地存在于篮球比赛的技术和战术之中.篮球规则的修改是从时间和空间入手,逐渐细化和严格起来的,规则的修改促进了篮球技术和战术的不断发展.现代篮球的基本战术是基于对时空的不同侧重而建立起来的时空框架,从时空的视角审视篮球有利于加深对现代篮球战术的理解.     

网络环境下图情学与管理学老化规律及其比较研究

选择基于网络的引文数据库CSSCI 2006-2009年间管理学和图书情报与文献学学科领域的33 4689条引文数据,进行两学科的负指数老化模型分析、老化指标分析。研究发现,在网络环境下,这两个学科都符合负指数的老化规律,管理学的学科稳定性要比图书情报与文献学好,而图书情报与文献学的老化速度要比管理学快。本文近似地计算出了目前阶段这两个学科的半衰期分别为4.64年、5.29年;普莱斯指数分别为0.54、0.47;最大引文年限分别为2年、3年。     

航海类专业学生补考时间选择对补考通过率影响的相关研究

通过对某航海院校不同学期相同补考科目学生121人,不同补考时间对补考通过率影响进行分析,得出于开学后三周内完成补考学生的通过率低于假期补考学生。最终确定补考时间的选择可以影响补考通过率,于开学后三周内完成补考学生的通过率较低。建议将补考时间规定为假期结束前l周。     

一种改进的万有引力搜索算法——TSP问题为例

本文旨在找到一种改进的万有引力搜索算法,快速准确解决组合优化问题,以最小旅行距离为目标的经典商人旅行问题为例,使用实数编码,并将连续数值区间的位置变量映射到离散的组合排序,即可行的旅行方案;为了有效地避免算法陷入局部最优解,使用模拟退火算法进行局部扩展搜索,进一步提高解的质量;最后通过仿真对比,得出结合模拟退火算法的万有引力搜索算法具有收敛速度快,精度高的特点这一结论。     

System Analysis for Oxygen Uptake Kinetics with Step and Pseudorandom Binary Sequence Exercise in Endurance Athletes

We examined whether the system analysis for step and pseudorandom binary sequence (PRBS) exercises could be useful to characterize oxygen uptake (VO₂) kinetics of female sedentary subjects and endurance athletes. Breath-by-breath VO₂ was determined during step- and PRBS-cycle ergometer exercises. The time course of the VO₂ kinetics was evaluated by the time constant of the second phase, which should reflect the adjustment of the oxidative metabolism at the skeletal muscle level. The VO₂ kinetics were significantly faster in long-distance runners than in sedentary subjects for both exercises. A significant relationship was observed in the VO₂ kinetics obtained from step and PRBS exercises. In each group, there was no significant difference in the VO₂ kinetics for step and PRBS exercises. These results indicated that the system analysis with PRBS exercises revealed the faster VO₂ kinetics in endurance athletes than in sedentary subjects.     

Characteristics of the start in women's World Cup skeleton

This study characterizes key elements of the start in elite female World Cup skeleton athletes. The top 20 female competitors in three World Cup races were videotaped within a calibrated space to allow the following components of the start to be quantified: (1) acceleration (velocity at 15-m mark, time to 15-m mark), (2) capacity (time to load, total number of steps to load), and (3) load (velocity at 45-m mark). A correlation analysis was used to establish the relationship between the variables of interest and overall start time (15- to 65-m mark). Velocity at the 15-m mark accounted for 86% of the variance in overall start time at St. Moritz and 85% at Sigulda. A stepwise regression analysis revealed that approximately 89% of the variation in start time could be explained by velocity at the 15-m mark, time to load, and velocity at the 45-m mark. Of the variables analysed in this study, rapid acceleration to attain a high velocity at the 15-m mark was the most important component of a fast overall start time. The importance of the time to load and velocity at the 45-m mark vary according to the different track characteristics.     

渝派地产与川派地产之比较

渝派地产以重庆主城区楼盘为代表,川派地产以成都地产为代表。重庆地形起伏大,城市发展速度迅猛,生活节奏较快;天府之国的成都平原地形平坦,城市发展悠久,生活比较悠闲。城市地域差异导致渝派地产与川派地产之间在楼盘建筑风格、地产商发展模式、建筑布局、高端住宅设计意向以及地产规划等方面都存在着一定的差异。无论是渝派地产的"山水特色",还是川派地产的"田园风格",都旨在为居民提供一个舒适的生活环境,为城市构建一个协调的布局,最终实现城市与自然的和谐发展。     

中国边境省区入境旅游发展的时间同步性与区域响应

依据1980—2011年中国边境9省区入境旅游客流量和旅游收入数据,分析其入境旅游发展的时间同步性与区域响应,结果表明:中国边境省区入境旅游可分为1980—1991年的缓慢增长期、1992—2003年的快速增长期和2004—2011年的加速增长期3个发展阶段;边境9省区入境旅游的增长变化、波动周期大致相同,但相关系数较低;各边境省区入境旅游发展还存在着较大的差异。依据基准年数值划分边境各省区各阶段入境旅游发展的起点,依据平均增速划分边境各省区各阶段入境旅游的发展速度,可动态地刻画不同省区不同阶段入境旅游的发展态势,揭示各省区入境旅游发展的区域响应,并为各省区入境旅游发展的动态比较研究和旅游发展规划制定提供参考依据。