不同频率全身振动刺激对运动员下肢肌群力量训练效果的对比研究

采用PHYSIO PLATE振动训练台,对北京优秀垒球、女子游泳及女子跳水运动员进行同振幅下不同频率振动刺激力量训练,并采用MERAC等速肌力测试系统,对实验前后以及实验中运动员下肢肌力变化情况进行对比研究。研究发现,抗负荷力量训练附加振动刺激可以有效地提高力量训练的效果,能够以相对较小的负荷有效地提高肌肉的最大力量、爆发力以及肌肉耐力;同振幅下,次高频(35Hz～50Hz)振动刺激对肌肉最大力量、快速力量、爆发力以及肌肉耐力的训练效果显著高于中低频(25Hz～35Hz)振动刺激。     

腰部竖脊肌疲劳运动过程中表面肌电信号线性和非线性指标的变化

通过等长背伸运动负荷诱发腰部竖脊肌疲劳并记录全程表面肌电（sEMG）信号,分别以快速傅立叶变换（FFT）计算平均功率频率MPF和非线性RQA方法计算确定性线段百分数（?T）。结果显示,MPF随着肌肉疲劳的发展而逐渐下降,而?T呈现反向变化趋势,提示肌肉疲劳时的sEMG信号规律性在增强。?T的变异系数CV比MPF的小,说明?T作为腰部肌肉功能状态的评价指标具有独特的优势。     

城镇化影响农村居民消费的地区差异及门槛效应?

推进城镇化是增加我国农村消费需求,扩大内需的重要突破口。采用2002—2012年我国省际面板数据考察城镇化、农村人口结构、消费结构升级等因素对农村居民消费的影响,结果表明：城镇化对农村居民消费增长具有显著的促进作用,且存在地区差异,东部地区城镇化对农村居民消费增长的作用大于西部地区;城镇化对我国农村居民消费的影响存在显著的单一门槛效应,门槛估计值为0．589,在城镇化水平高（大于0．589）的地区,城镇化对农村居民消费的促进作用更大,但目前我国大部分省区的城镇化水平还未达到门槛值。应进一步加快我国城镇化进程,尤其是中西部次发达地区的城镇化进程,充分发挥城镇化对农村居民消费的促进作用。     

Are gait characteristics and ground reaction forces related to energy cost of running in elite Kenyan runners?

The aim of this study was to determine whether gait cycle characteristics are associated with running economy in elite Kenyan runners. Fifteen elite Kenyan male runners completed two constant-speed running sets on a treadmill (12 km ·h^?1 and 20 km ·h^?1). VO₂ and respiratory exchange ratio values were measured to calculate steady-state oxygen and energy cost of running. Gait cycle characteristics and ground contact forces were measured at each speed. Oxygen cost of running at different velocities was 192.2 ± 14.7 ml· kg^?1· km^?1 at 12 km· h^?1 and 184.8 ± 9.9 ml· kg^?1· km^?1 at 20 km· h^?1, which corresponded to a caloric cost of running of 0.94 ± 0.07 kcal ·kg^?1·km^?1 and 0.93 ± 0.07 kcal· kg^?1· km^?1. We found no significant correlations between oxygen and energy cost of running and biomechanical variables and ground reaction forces at either 12 or 20 km· h^?1. However, ground contact times were ~10.0% shorter (very large effect) than in previously published literature in elite runners at similar speeds, alongside an 8.9% lower oxygen cost (very large effect). These results provide evidence to hypothesise that the short ground contact times may contribute to the exceptional running economy of Kenyan runners.     

不凝结气体对蒸汽浸没射流压力振荡的影响

通过实验研究不凝结气体（空气）对蒸汽浸没射流压力振荡特性的影响。结果表明：不凝结气体存在时压力振荡强度比纯蒸汽浸没射流时明显减小。随空气质量分数的增加,压力振荡峰值的位置沿轴向后移。过冷水温低于45℃时,峰值随空气质量分数的增加而增大;高于50℃时,随空气质量分数的增加而减小;水温在45~50℃之间时,峰值大致相同。压力振荡主频随空气质量分数、蒸汽质量流率和过冷水温度的增加而减小。     

Optimal sampling frequency in recording of resistance training exercises

The purpose of this study was to analyse the raw lifting speed collected during four different resistance training exercises to assess the optimal sampling frequency. Eight physically active participants performed sets of Squat Jumps, Countermovement Jumps, Squats and Bench Presses at a maximal lifting speed. A linear encoder was used to measure the instantaneous speed at a 200 Hz sampling rate. Subsequently, the power spectrum of the signal was computed by evaluating its Discrete Fourier Transform. The sampling frequency needed to reconstruct the signals with an error of less than 0.1% was f_99.9 = 11.615 ± 2.680 Hz for the exercise exhibiting the largest bandwidth, with the absolute highest individual value being 17.467 Hz. There was no difference between sets in any of the exercises. Using the closest integer sampling frequency value (25 Hz) yielded a reconstruction of the signal up to 99.975 ± 0.025% of its total in the worst case. In conclusion, a sampling rate of 25 Hz or above is more than adequate to record raw speed data and compute power during resistance training exercises, even under the most extreme circumstances during explosive exercises. Higher sampling frequencies provide no increase in the recording precision and may instead have adverse effects on the overall data quality.     

《奥林匹克2020议程:奥运会新规范》改革关键点及北京冬奥会的践行策略研究

《奥林匹克 2020议程：奥运会新规范》(下文简称《新规范》)是当前国际奥委会系列改革的前沿指导文件,对 2022年北京冬奥会具有重要的指导价值。文章对《新规范》进行了文本解析,归纳了《新规范》的 5个改革关键点：降低办奥成本、优化遗产举措、促进组织善治、提升品牌影响、改善服务水平。 鉴于当前北京冬奥会的筹办进展与现实需求,探讨北京冬奥会后续系列工作对改革关键点的践行策略： 规划场馆后续运营、能源消耗与资金利用的行动方案;不断完善遗产发展方案,确保遗产与城市协调发展;促进利益相关者的协同参与,提升赛事治理能力;借鉴国内外优秀经验,制定本土文化教育战略;围绕服务体系的核心领域,不断提升赛事水准。     

单自由度体系频率分析的教学探究

各质点惯性力不共线的单自由度体系的频率分析,是结构动力学教学中的一个难点。文章利用理论力学中的知识,将单自由度质点系平动时的频率计算公式ω=1/（mδ）推广到了单自由度质点系转动时的的频率计算问题,并给出了相应的转动柔度系数的确定方法。这样的处理也启发了学生将各门课程的知识进行融会贯通。     

用MF14万用表快速测定电视机行逆程脉冲幅值

通过对MF14万用表结构的理论分析,推导出了电视机行脉冲幅度值与万用表指示值的关系,从而给出了一种快速测定行脉冲幅值的方法。     

世界优秀男子短距离自由泳运动员参加第27届奥运会技、战术分析

通过对第27届奥运会游泳比赛男子短距离自由泳前8名运动员技、战术的数理统计研究发现,男子短距离自由泳技术结构发生较大变化,划频有较大幅度提高,划幅有所缩短.霍根班德在100m自由泳比赛中运用"后发制胜”的战术,能较好地控制前、后程节奏与速度,发挥了最佳竞技状态,创造了该项目的世界纪录.克里姆运用"先发制人”的战术,从比赛一开始就以超出所有对手的速度领先游进,并在全程中始终保持这种优势,表现出强劲的潜在能力.