Forthcoming events

The proximal-to-distal segmental sequence has been identified in many sports activities, including baseball pitching and ball kicking. However, proximal-to-distal sequential muscle activity has not been identified. The aims of this study were to establish whether sequential muscle activity does occur and, if it does, to determine its functional role. We recorded surface electromyograms (EMGs) for 17 muscles from the upper extremity and abdomen during overarm throwing and detected the onset and peak times as indices of muscle activity. The following electromyographic properties were commonly identified in the participants. First, sequential muscle activity was observed from the scapular protractors to the shoulder horizontal flexors and from the shoulder horizontal flexors to the elbow extensor, but not from the elbow extensor to the wrist flexor or forearm pronator. Secondly, the external oblique contralateral to the throwing arm became activated before the ipsilateral external oblique. This sequence is considered to be very effective for the generation of high force and energy in the trunk. Thirdly, the ipsilateral external oblique began its activity almost at foot strike. Finally, the main activity of the rectus abdominis appeared just before the point of release.     

基于三层交换的VLAN技术与实现

随着网络规模的扩大，网络上大量的广播信息导致网络传输效率低下，为了解决这个问题，产生了虚拟局域网技术(VLAN)。VLAN是在交换网络的基础上构建可跨越不同网段、不同网络的端到端的逻辑网络，从而避免了园区网广播风暴的出现，提高交换式园区网的整体性能和安全性及可扩展性。章立足于具体应用提出了基于虚拟局域网技术和网络安全技术来构建一个合理安全的校园园区网的实现方案。     

基于软交换的下一代网络组网方案

首先分析了软交换和下一代网络的概念，然后介绍了软交换网络的组网需求，最后对各种组网方案做了分析比较，并提出了关于下一代网络组网的建议。     

浅议负载均衡技术在计算机网络中的应用

在Internet迅猛发展的今天，网络的可用性和容错性已成为对站点的关键要求。而负载均衡技术的出现，极大地保证了网络核心部件的正常运转，扩展了网络带宽，提高了吞吐量，加强了网络数据处理能力，大大提高了系统容错性，为最终用户提供优质的服务质量。本文就几种常用的负载均衡技术展开讨论、进行了技术分析，同时分析了负载均衡技术在实施过程中要注意的几个问题。     

Acute kinematic and kinetic adaptations to wearable resistance during vertical jumping

One variation of vertical jump (VJ) training is resisted or weighted jump training, where wearable resistance (WR) enables jumping to be overloaded in a movement specific manner. A two-way analysis of variance with Bonferroni post hoc contrasts was used to determine the acute changes in VJ performance with differing load magnitudes and load placements. Kinematic and kinetic data were quantified using a force plate and contact mat. Twenty sport active subjects (age: 27.8?±?3.8 years; body mass (BM): 70.2?±?12.2?kg; height: 1.74?±?0.78?m) volunteered to participate in the study. Subjects performed the counter movement jump (CMJ), drop jump (DJ) and pogo jump (PJ) wearing no resistance, 3% or 6% BM affixed to the upper or lower body. The main finding in terms of the landing phase was that the effect of WR was non-significant (P?>?.05) on peak ground reaction force. With regard to the propulsive phase the main findings were that for both the CMJ and DJ, WR resulted in a significant (P?<?.05) decrease in jump height (CMJ: ?12% to ?17%, DJ: ?10% to ?14%); relative peak power (CMJ: ?8% to ?17%, DJ: ?7% to ?10%); and peak velocity (CMJ: ?4% to ?7%, DJ: ?3% to ?8%); while PJ reactive strength index was significantly reduced (?15% to ?21%) with all WR conditions. Consideration should be given to the inclusion of WR in sports where VJ’s are important components as it may provide a novel movement specific training stimulus.

Highlights

• WR of 3 or 6 % BM provided a means to overload the subjects in this study resulting in decreased propulsive power and velocity that lead to a reduced jump height and landing force.

• Specific strength exercises that closely mimic sporting performance are more likely to optimise transference, therefore WR with light loads of 3–6% body mass (BM)appear a suitable tool for movement specific overload training and maximising transference to sporting performance.

• Practitioners can safely load their athletes with upper or lower body WR of 3–6% BM without fear of overloading the athletesover and above the landing forces they are typically accustomed too.

• As a training stimulus it would seem the WR loading provides adequate overload and athletes should focus on velocity of movement to improve power output and jump height i.e. take-off velocity.

     

Vlan在企业网中的应用

本文通过一个企业网中Vlan的规划和配置的具体实施案例,来说明Vlan技术在现有大中型企业网当中的具体应用。     

IEEE 802 1Q VLAN原理实验的设计与实现

VLAN原理实验利用协议分析方法,测试验证VLAN实现的功能,以及交换机不同属性端口接收、转发普通帧和标记帧的特性,观察支持VLAN的交换机对以太帧插入、删除802.1Q标记的过程。并通过错误配置交换机端口属性,演示交换机加、去标记失配导致的网络故障,以加深学生对IEEE 802.1Q VLAN原理的理解。     

Do oarsmen have asymmetries in the strength of their back and leg muscles?

The aim of this study was to establish whether asymmetry of the strength of the leg and trunk musculature is more prominent in rowers than in controls. Nineteen oarsmen and 20 male controls matched for age, height and body mass performed a series of isokinetic and isometric strength tests on an isokinetic dynamometer. These strength tests focused on the trunk and leg muscles. Comparisons of strength were made between and within groups for right and left symmetry patterns, hamstring :quadriceps ratios, and trunk flexor and extensor ratios. The results revealed no left and right asymmetries in either the knee extensor or flexor strength parameters (including both isometric and isokinetic measures). Knee extensor strength was significantly greater in the rowing population, but knee flexor strength was similar between the two groups. No difference was seen between the groups for the hamstring:quadriceps strength ratio. In the rowing population, stroke side had no influence on leg strength. No differences were observed in the isometric strength of the trunk flexors and extensors between groups, although EMG activity was significantly higher in the rowing population. Patterns of asymmetry of muscle activity were observed between the left and right erector spinae muscles during extension, which was significantly related to rowing side ( P < 0.01). These observations could be related to the high incidence of low back pain in oarsmen.