Ground reaction forces of Olympic and World Championship race walkers

Race walking is an Olympic event where no visible loss of contact should occur and the knee must be straightened until midstance. The purpose of this study was to analyse ground reaction forces of world-class race walkers and associate them with key spatiotemporal variables. Nineteen athletes race walked along an indoor track and made contact with two force plates (1000 Hz) while being filmed using high-speed videography (100 Hz). Race walking speed was correlated with flight time (r = .46, p = .049) and flight distance (r = .69, p = .001). The knee's movement from hyperextension to flexion during late stance meant the vertical push-off force that followed midstance was smaller than the earlier loading peak (p < .001), resulting in a flattened profile. Athletes with narrower stride widths experienced reduced peak braking forces (r = .49, p = .046), peak propulsive forces (r = .54, p = .027), peak medial forces (r = .63, p = .007) and peak vertical push-off forces (r = .60, p = .011). Lower fluctuations in speed during stance were associated with higher stride frequencies (r = .69, p = .001), and highlighted the importance of avoiding too much braking in early stance. The flattened trajectory and consequential decrease in vertical propulsion might help the race walker avoid visible loss of contact (although non-visible flight times were useful in increasing stride length), while a narrow stride width was important in reducing peak forces in all three directions and could improve movement efficiency.     

Effects of load mass carried in a backpack upon respiratory muscle fatigue

Purpose: The purpose of this study was to investigate whether loads carried in a backpack, with a load mass ranging from 0 to 20?kg, causes respiratory muscle fatigue. Methods: Eight males performed four randomised load carriage (LC) trials comprising 60?min walking at 6.5?km?h^?1 wearing a backpack of either 0 (LC₀), 10 (LC₁₀), 15 (LC₁₅) or 20?kg (LC₂₀). Inspiratory (P_Imax) and expiratory (P_Emax) mouth pressures were assessed prior to and immediately following each trial. Pulmonary gas exchange, heart rate (HR), blood lactate and glucose concentration and perceptual responses were recorded during the first and final 60?s of each trial. Results: Group mean P_Imax and P_Emax were unchanged following 60-min load carriage in all conditions (p?>?.05). There was an increase over time in pulmonary gas exchange, HR and perceptions of effort relative to baseline measures during each trial (p?p?>?.05). Conclusions: These findings indicate that sub-maximal walking with no load or carrying 10, 15 or 20?kg in a backpack for up to 60?min does not cause respiratory muscle fatigue despite causing an increase in physiological, metabolic and perceptual parameters.     

声乐表演的二度创造--谈歌曲演唱的创作方法

从声乐表演的基本属性出发 ,阐明了歌曲声乐表演“从外到内”、再“从内到外”的分析、体验、表现作品的创作方法     

计算机处理器性能的衡量

处理器在整个计算机中占了很重要的部分,很多用户都关心处理器的性能表现如何以及怎样衡量它的性能.作者主要从两个方面介绍其性能的技术参数指标.     

议政府采购绩效审计

如何开展政府采购绩效审计,是审计机关及其审计人员亟须研究解决的一个课题。实施政府采购绩效审计,就必须从审计角度出发,就政府采购绩效审计的必要性、审计目标、审计的依据和内容进行思考。     

谈谈声乐表演专业学生的嗓音保护

透视当前嗓音保护的现象,阐述了嗓音保护的重要性,并结合教学实践,提出了一些保护嗓音的可行性方法.     

法律保护、控股股东与公司绩效分析

我国上市公司具有典型的股权集中特征,研究控股股东行为对于改善我国公司治理具有重要意义。控制权收益是控股股东最大化自身利益的载体。现实决策中,控股股东往往需要权衡公共收益和私人收益哪一个更有利于实现自身利益最大化。文章从法律保护角度出发,以控制权收益为切入点,构建了一个研究控股股东行为的分析框架。结合我国控股股东的实际情况,将该框架进一步具体化,用来解释我国国有控股公司与民营控股公司的绩效差异之谜。     

鲁迅的责任感

鲁迅的责任感是他情感体系中的一种根本情绪。这种责任感表现在家庭、社会、教育、创作等几个方面。同时,责任感的产生也是伴随时间积累而不断萌发和深化的,求学生活的影响、越地文化的哺育、社会实践的锻炼、中外典籍的熏陶都共同作用于鲁迅责任感的产生过程。鲁迅的责任感对于他个人的生命历程、社会发展和民众思想都有重大的意义,这种责任感成就了鲁迅的伟大,也成就了伟大的时代和拯救了危机的民族,可谓意义深远。     

数据中心节能环保研究

随着业务的增长,服务器数量的增加,大型数据中心的能耗成本也迅速增加,并有赶超硬件成本的趋势.因此,数据中心运营商除采用节能环保的硬件外,还在电源管理技术方面进行优化,但单凭硬件优化方案还难以挖掘潜力.包括硬、软件在内的所有相关因素都应当考虑,才能使能效最大化.我们就能效与硬件和软件等相关因素进行分析,讨论了数据中心节能的各种途径,提出了构建节能环保、低能耗的绿色数据中心的建议.