Lower limb joint kinetics and ankle joint stiffness in the sprint start push-off

Sprint push-off technique is fundamental to sprint performance and joint stiffness has been identified as a performance-related variable during dynamic movements. However, joint stiffness for the push-off and its relationship with performance (times and velocities) has not been reported. The aim of this study was to quantify and explain lower limb net joint moments and mechanical powers, and ankle stiffness during the first stance phase of the push-off. One elite sprinter performed 10 maximal sprint starts. An automatic motion analysis system (CODA, 200 Hz) with synchronized force plates (Kistler, 1000 Hz) collected kinematic profiles at the hip, knee, and ankle and ground reaction forces, providing input for inverse dynamics analyses. The lower-limb joints predominately extended and revealed a proximal-to-distal sequential pattern of maximal extensor angular velocity and positive power production. Pearson correlations revealed relationships (P < 0.05) between ankle stiffness (5.93 ± 0.75 N x m x deg(-1)) and selected performance variables. Relationships between negative power phase ankle stiffness and horizontal (r = -0.79) and vertical (r = 0.74) centre of mass velocities were opposite in direction to the positive power phase ankle stiffness (horizontal: r = 0.85; vertical: r = -0.54). Thus ankle stiffness may affect the goals of the sprint push-off in different ways, depending on the phase of stance considered.     

Indirect estimation of cable tension during gymnastic movements on rings

Knowledge of external forces acting on an athlete is often required to study performance and injury mechanisms, but direct measurements are difficult to obtain. While transducers in the rings cables typically measure external forces experienced by gymnasts performing static balances and swinging movements on rings, this solution is not always acceptable and an accurate technique that does not hinder the gymnasts’ performances is desirable. This study evaluates a video-based technique for estimating cable tension on the rings apparatus. Static loading of a rings frame coupled with a planar video analysis of the mandatory damped elastic devices (DEDs) provided a tension-deflection calibration curve. Three-dimensional video and cable tension data were obtained for two male gymnasts performing static balances and dynamic swinging movements. Cable tension was measured using a force link while a planar video analysis determined time histories of the DED deflections. Combined cable tension time histories were estimated fromrelative DED deflections coupled with the tension-deflection calibration curve and the orientation of the rings cables, and were compared to measured values to evaluate the proposed technique. For static balances the RMS difference between measured and estimated combined cable tension was 83 N. For dynamic swinging movements the maximum RMS difference was 189 N, equivalent to a 4% difference when expressed as a percentage of the peak value. The indirect video-based technique developed in this study accurately estimates combined cable tension throughout movements on rings and may be considered for studies where a remote measurement is required. There is potential for the technique to be extended to other sporting situations, where indirect accurate estimates of external forces acting on an athlete are needed.     

Measuring running speed using photocells.

Photocell timing systems are used routinely to measure running speeds. In this study, the accuracy of such systems was evaluated using centre of mass speed estimates from three-dimensional video analysis as criteria. One subject ran at five nominal speeds (5-9 m x s(-1)) for each of five separations (1.6-2.4 m) between consecutive photocells. Running speeds were calculated from the photocell data using single beam and double beam systems. For single beam systems, the start of the first break of a beam and the start of the longest break of a beam were used as trigger criteria. For double beam systems, the first occurrence of both beams being broken and the start of the longest double break were used as trigger criteria. Root mean square speed errors were smaller for the double beam systems. The longest break criterion gave smaller root mean square errors than the first break criterion. In general, errors in speed were smaller for greater photocell separations. An error of 0.1 m x s(-1) was achieved using a single beam system set at hip height with a longest break criterion for photocell separations of around two stride lengths. The advantage of using a double beam system is that it achieves this accuracy without the need to adjust photocell separation for different stride lengths.     

The conceptual process of skill progression development in artistic gymnastics

In this study, we examined the methods used and knowledge required by 16 elite men's gymnastic coaches in the development of skill progressions. Following in-depth interviews, a conceptual model representing the process of skill progression development was generated. We found that: (1) elite gymnastic coaches developed skill progressions through experimental practice, reflection and critical inquiry; (2) the development of skill progressions was underpinned by the coaches acquiring a mindset based on four further sub-components (i.e. skill progression refinement, current coaching knowledge, mental imagery and biomechanical understanding); and (3) coaches identified the importance of replication of the spatial and temporal characteristics of the final skill. The results are consistent with task analysis, reflective practice and the principle of specificity. Practically, these findings suggest the need to develop coaches with a more objective approach to skill progression development and a greater understanding of the controlling mechanisms inherent in such practices.     

论图书馆硬盘阵列系统的安全体系

通过对工作中实践经验的总结及多种硬盘阵列资料的比较和分析，对目前图书馆大容量存储系统的主流设备——硬盘阵列做了概括性的介绍，并从多个方面较全面地论述了硬盘阵列系统的安全体系设计。     

用PHP-Nuke架设和管理图书馆动态网站经验谈

介绍使用PHP－Nuke系统架设和管理图书馆动态网站时碰到的一些问题以及解决这些问题的方法。     

Calculating upper limb inertial parameters.

In the kinematic and kinetic analysis of human movement, an accurate assessment of the inertial properties of the body segments under investigation is often essential. Statistical and geometric models of the segments of the upper limb were examined to determine their ability to predict the moments of inertia of these segments. The cadaver data of Chandler et al. (1975) were used as the criteria with which computed values were compared. The regression equations of Hinrichs (1985) gave the most accurate results; the geometric models appeared to offer the greatest flexibility.     

面向工业机器人专业的混合式教学系统

近年来,随着信息技术的不断发展,工业机器人在自动化、智能化、标准化和定制化生产制造领域的应用 日益广泛.针对目前工业机器人人才严重短缺和人才培养条件不足问题,本文提出了一种面向工业机器人专业的线上线下混合式教学系统,包括具备理论、示教、仿真、编程有机集成的线上、线下混合式培训功能的教学软件,集编程、操作、二次开发等为一体的示教与仿真综合实训系统,以及工业机器人技术资源服务平台.利用该混合式教学系统,可实现教学软件、实训系统及技术资源服务平台的有机结合,为开发适合工业机器人专业的教学系统提供了有效途径.     

论诗歌韵式与音乐调式的同构性

音乐美是中外古典格律诗歌有别于其他文体的基本特征,诗歌韵式与音乐调式具有同构性。本文具体分析诗歌韵式与音乐调式的组织功能、音乐调式和诗歌韵部的色彩、音乐的转调和诗歌的转韵、调式和韵式对节奏的影响、汉诗"衬韵"与西洋"ab"韵等同构关系,从中外传统诗歌韵式中为新诗韵建设提供借鉴的合理内核。