Understanding the influence of perceived fatigue on coordination during endurance running

ABSTRACT

During the course of a training programme, runners will typically increase running velocity and volume possibly encountering fatigue during a run, which is characterised as a feeling of general tiredness. The purpose of the current study was to identify whether or not level of perceived fatigue affects coordination and coordination variability in healthy runners during the recovery velocity of an endurance interval run. A total of 20 endurance runners completed a 1-hour run that included running velocity intervals at 75% of estimated 10 k race pace (5 minutes) and estimated 10 k race pace (1 minute). After each run, participants completed a fatigue questionnaire and were grouped based on their post-run self-reported perceived fatigue. 3D motion capture data were collected during the run and analysed to generate coordination patterns and variability of the patterns as dependent variables. Multiple mixed model ANOVAs were conducted to test for differences between perceived fatigue groups. Coordination and variability differences were reported in a number of couplings during transition phases (late and early stance) and events (toe-off and foot contact) of the gait cycle. It was concluded that the level of perceived fatigue affected coordination and coordination variability during the recovery velocity of a 1-hour interval run.     

Reactive and eccentric strength contribute to stiffness regulation during maximum velocity sprinting in team sport athletes and highly trained sprinters

ABSTRACT

This study investigated the role of reactive and eccentric strength in stiffness regulation during maximum velocity sprinting (Vmax) in team sport athletes compared with highly trained sprinters. Thirteen team sport athletes and eleven highly trained sprinters were recruited. Vmax was measured using radar, and stiffness regulation was inferred from modelled vertical and leg spring stiffness. Reactive strength (RSI) was determined from a 0.50 m drop jump, and an eccentric back squat was used to assess maximum isoinertial eccentric force. Trained sprinters attained a higher Vmax than team sport athletes, partly due to a briefer contact time and higher vertical stiffness. Trained sprinters exhibited a moderately higher RSI via the attainment of a briefer and more forceful ground contact phase, while RSI also demonstrated large to very large associations with vertical stiffness and Vmax, respectively. Isoinertial eccentric force was largely correlated with Vmax, but only moderately correlated with vertical stiffness. Reactive and eccentric strength contribute to the ability to regulate leg spring stiffness at Vmax, and subsequently, the attainment of faster sprinting speeds in highly trained sprinters versus team sport athletes. However, stiffness regulation appears to be a task-specific neuromuscular skill, reinforcing the importance of specificity in the development of sprint performance.     

钢管混凝土双肢格构墩梁桥抗震优化设计

以黄桷湾特大桥为工程背景,选取轴压比、梁墩刚度比、系梁布置形式及柱肢混凝土强度等级为设计参数,应用Midas Civil有限元软件构造了20座三跨对称桥梁计算模型。研究E1地震作用下钢管混凝土双肢格构墩连续梁桥主要控制截面参数地震响应,探讨各设计参数对钢管混凝土双肢格构墩连续梁桥抗震性能的影响规律,并对全桥进行优化验证。研究结果表明:轴压比对地震作用下结构内力和位移有一定影响,建议控制在0.15~0.25;梁墩刚度比对结构的抗震性能影响较大,控制在4.08~10.90时结构的内力分布更加合理;核心混凝土的强度在C40~C50时取值较为合理。     

半刚性连接节点的类型及其受力性能

半刚性连接是目前常用的一种梁柱连接形式,以其施工方便、抗震性能好而得到推广.但是此类节点受力复杂,而且目前国内对此类节点的设计方法缺乏具体规范.本文给出了几种半刚性连接的类型以及梁柱连接的弯矩.转角曲线,考虑节点半刚性连接的线性模型,介绍了初始刚度的计算公式,从而为半刚性节点的设计和应用提供参考.     

马拉松不同水平业余男子选手训练学和肌力特征比较

对完成2016年北京马拉松、上海国际马拉松的258名男性业余选手赛前1周内进行训练学特征问卷和体能测试,将规定时间完成比赛且赛后1周完成伤病排查随访者193人纳入研究。根据2018年新增分级标准：A组118人、B组65人、C组10人。结果显示,周训练平均配速3组间均存在显著差异[A组（9.6±3.4） km/h、B组（11.8±4.0） km/h、C组（13.7±6.4） km/h];安排抗阻训练A组（56.2%）与B组 （66.2%）和C组（70.7%）存在显著差异;安排间歇训练3组间均存在显著差异（A组40.6%、B组 50.2%、C组69.8%）（P＜0.05）;单腿跳相对值和单腿跳对称性A组（78.53%±12.43%、73%±13%）与B组（85.37%±12.80%、81%±14%）、C组（91.70%±11.43%、87%±12%）间存在显著差异;卷腹次数C组（61.00±62.27）次与A组（24.90±27.91）次、B组（35.95±26.40）次间存在显著差异（P＜0.05）。表明不同级别业余马拉松选手的主要训练差异为抗阻训练和间歇训练的参与度,与成绩相关的肌力特征指标有单脚跳相对值、单脚跳对称性和卷腹次数,下肢刚度未见差异。     

Effect of sex and fatigue on muscle stiffness and musculoarticular stiffness of the knee joint in a young active population

The purpose of this study was to investigate the influence of sex and fatigue on knee extensor peak torque (PT), muscle stiffness (MS) of the vastus lateralis (VL) and knee joint musculoarticular stiffness (MAS) in young adults. Twenty-two male and 22 female recreational athletes participated. Males were characterised by higher relaxed [pre-: males 364.43 (52.00) N · m^–1, females 270.27 (37.25) N · m^–1; post-: males 446.75 (83.27) N · m^–1, females 307.39 (38.58) N · m^–1] and contracted [pre-: males 495.07 (71.04) N · m^–1, females 332.34 (85.42) N · m^–1; post-: males 546.37 (90.74) N · m^–1, females 349.21 (85.55) N · m^–1] MS of the VL, and knee joint MAS [pre-: males 1450.11 (507.98) N · m^–1, females 1027.99 (227.33) N · m^–1; post-: males 1345.81 (404.90) N · m^–1, females 952.78 (192.38) N · m^–1] than females pre- and post-fatigue. A similar finding was observed in pre-fatigue normalised knee extensor PT [pre-: males 2.77 (0.42) N · m kg^–1, females 2.41 (0.40) N · m kg^–1, post-: males 2.53 (0.54) N · m kg^–1, females 2.26 (0.44) N · m kg^–1]. After the fatigue protocol, normalised knee extensor PT and knee joint MAS decreased, whilst relaxed and contracted MS of the VL increased in both sexes. These observed differences may contribute to the higher risk of knee injury in females and following the onset of fatigue.     

轧辊正火冷却过程中的热应力估计──偏微分方程数值解法的应用

用有限差分法模拟轧辊正火的冷却过程,得出温度场的一较大温度降低值,据此结果用有限单元法求出此时间内的场中各节点的位移;借以得出单元内的平均应力;且仅为热应力。然后进行热应力对轧辊断裂作用的分析讨论。     

半刚性节点框架的二阶侧移简化计算

为了研究在框架侧移过程中,p-delta效应与连接柔性对其的影响。以半刚性连接框架为研究对象。在考虑p-delta效应和连接非线性的基础上,对轴力放大系数13进行了重新的计算修正,推出了可以考虑多重几何非线性的侧移简化计算公式,该公式更符合框架的实际特性。算例计算结果表明：简化计算公式力学概念清晰,应用方便且计算精度较高,可用于结构的初步设计和最终校核。     

机床机械结合面接触刚度模型研究概况

结合面接触问题对数控机床动态特性影响非常大,是决定机床系统总刚度和总阻尼的主要因素.本文总结了机床机械结合面接触刚度研究中常用的三种模型,即赫兹接触模型、G-W统计接触模型和分形接触模型,并根据三维W-M函数,利用Matlab仿真模拟了表面的三维粗糙形貌,分析了分形参数G和D的含义.     

底座板伸缩刚度对大跨度连续梁桥上CRTSⅡ型板式无砟轨道纵向力的影响

在结构特点分析的基础上,考虑层间传力关系和横向相邻股道的影响,建立了大跨度连续梁桥上CRTSⅡ型板式无砟轨道纵向力计算的空间一体化模型和求解方法。计算分析了列车制动和温度变化作用下底座板伸缩刚度对大跨度连续梁桥上CRTSⅡ型板式无砟轨道纵向力的影响规律,结果表明:列车制动和温度变化作用下系统纵向力变化规律相同,随着底座板伸缩刚度降低,钢轨和桥梁墩台纵向力增加,复合板、剪力齿槽和端刺纵向力减小。