To explore the influence of spatially varying ground motion on the dynamic behavior of a train passing through a three-tower cable-stayed bridge,a 3D train–track–bridge coupled model is established for accurately si...To explore the influence of spatially varying ground motion on the dynamic behavior of a train passing through a three-tower cable-stayed bridge,a 3D train–track–bridge coupled model is established for accurately simulating the train–bridge interaction under earthquake excitation,which is made up of a vehicle model built by multi-body dynamics,a track–bridge finite element model,and a 3D rolling wheel–rail contact model.A conditional simulation method,which takes into consideration the wave passage effect,incoherence effect,and site-response effect,is adopted to simulate the spatially varying ground motion under different soil conditions.The multi-time-step method previously proposed by the authors is also adopted to improve computational efficiency.The dynamic responses of the train running on a three-tower cablestayed bridge are calculated with differing earthquake excitations and train speeds.The results indicate that(1)the earthquake excitation significantly increases the responses of the train–bridge system,but at a design speed,all the running safety indices meet the code requirements;(2)the incoherence and site-response effects should also be considered in the seismic analysis for long-span bridges though there is no fixed pattern for determining their influences;(3)different train speeds that vary the vibration characteristics of the train–bridge system affect the vibration frequencies of the car body and bridge.展开更多
Background: Running-related overuse injuries can result from the combination of extrinsic(e.g., running mileage) and intrinsic risk factors(e.g.,biomechanics and gender), but the relationship between these factors is ...Background: Running-related overuse injuries can result from the combination of extrinsic(e.g., running mileage) and intrinsic risk factors(e.g.,biomechanics and gender), but the relationship between these factors is not folly understood. Therefore, the first purpose of this study was to determine whether we could classify higher-and lower-mileage runners according to differences in lower extremity kinematics during the stance and swing phases of running gait. I he second purpose was to subgroup the runners by gender and determine whether we could classify higherand lower-mileage runners in male and female subgroups.Methods: Participants were allocated to the "higher-mileage" group(≥32 km/week; n= 41(30 females)) or to the "lower-mileage" group(≤25 km;n= 40(29 females)). Three-dimensional kinematic data were collected during 60 s of treadmill running at a self-selected speed(2.61 ± 0.23 m/s).A support vector machine classifier identified kinematic differences between higher-and lower-mileage groups based on principal component scores.Results: Higher-and lower-mileage runners(both genders) could be separated with 92.59% classification accuracy. When subgrouping by gender,higher-and lower-mileage female runners could be separated with 89.83% classification accuracy, and higher-and lower-mileage male runners could be separated with 100% classification accuracy.Conclusion: These results demonstrate there are distinct kinematic differences between subgroups related to both mileage and gender, and that these factors need to be considered in future research.展开更多
Background:Segment coordination variability(CV)is a movement pattern associated with running-related injuries.It can also be adversely affected by a prolonged run.However,research on this topic is currently limited.Th...Background:Segment coordination variability(CV)is a movement pattern associated with running-related injuries.It can also be adversely affected by a prolonged run.However,research on this topic is currently limited.The purpose of this study was to investigate the effects of a prolonged run on segment CV and vertical loading rates during a treadmill half marathon.Methods:Fifteen healthy runners ran a half marathon on an instrumental treadmill in a biomechanical laboratory.Synchronized kinematic and kinetic data were collected every 2 km(from 2 km until 20 km),and the data were processed by musculoskeletal modeling.Segment CVs were computed from the angle-angle plots of selected pelvis-thigh,thigh-shank,and shank-rearfoot couplings using a modified vector coding technique.The loading rate of vertical ground reaction force was also calculated.A one-way MANOVA with repeated measures was performed on each of the outcome variables to examine the main effect of running mileage.Results:Significant effects of running mileage were found on segment CVs(p≤0.010)but not on loading rate(p=0.881).Notably,during the early stance phase,the CV of pelvis frontal thigh frontal was significantly increased at 20 km compared with the CV at 8 km(g=0.59,p=0.022).The CV of shank transverse vs.rearfoot frontal decreased from 2 km to 8 km(g=0.30,p=0.020)but then significantly increased at both 18 km(g=0.05,p<0.001)and 20 km(g=0.36,p<0.001).Conclusion:At the early stance,runners maintained stable CVs on the sagittal plane,which could explain the unchanged loading rate throughout the half marathon.However,increased CVs on the frontal/transverse plane may be an early sign of fatigue and indicative of possible injury risk.Further studies are necessary for conclusive statements in this regard.展开更多
Running related foot injuries are associated with excessive foot movements due to malaligned foot structure and poor functional foot stability. Clinicians tape the foot to alleviate pain and prevent further injuries, ...Running related foot injuries are associated with excessive foot movements due to malaligned foot structure and poor functional foot stability. Clinicians tape the foot to alleviate pain and prevent further injuries, whilst allowing the athlete to continue training. However, the effect of taping is not conclusive. The purpose of this study is to investigate if taping effectively improves foot structure, functional foot stability and reduces excessive foot movements during running. Twenty-two subjects had their foot structure identified as： fiat foot stable, fiat foot unstable and normal arched unstable according to the FPI （foot posture index） and the Modified Romberg＇s Test with the BESS （balance error scoring system） criteria. The subjects ran on an instrumented treadmill barefooted with their feet taped and untaped. Running kinetic and kinematic data were collected and analysed using a paired t-test and 3x2 ANOVA. Taping improved foot structure but not functional foot stability. During running, taping significantly reduced rearfoot eversion. Taping increased the loading rate in the fiat foot and normal arched unstable groups but reduced the loading rate for the flat foot stable group. Implication on the appropriate use of foot taping was discussed.展开更多
为研究跑步运动中不同紧度护膝对膝关节防护效果的影响,以20名热爱跑步运动的健康女性作为实验对象,运用三维动态捕捉技术捕捉测试者佩戴不同紧度护膝在不同速度跑步下的膝关节三维角度数据,将实验数据进行相关数理统计分析与研究。从...为研究跑步运动中不同紧度护膝对膝关节防护效果的影响,以20名热爱跑步运动的健康女性作为实验对象,运用三维动态捕捉技术捕捉测试者佩戴不同紧度护膝在不同速度跑步下的膝关节三维角度数据,将实验数据进行相关数理统计分析与研究。从紧身压迫角度出发对跑步过程中膝关节三维角度进行探讨,为紧身运动护膝的开发研究提供理论指导。结果表明:紧身压迫是衡量膝关节固定效果的一个重要因素,施加表面防护载荷对膝关节起到了一定的固定束缚作用;护膝紧身压迫应控制在2.152 8~2.861 7 k Pa内,以满足运动过程中对膝关节的固定保护作用。该研究为运动防护装备开发提供了设计依据。展开更多
基金the National Natural Science Foundation of China(Grant No.51678576)the National Key R&D Program of China(Grant No.2017YFB1201204)+1 种基金China Railway Corporation R&D Project(Grant No.2015G001-G)the Fundamental Research Funds for the Central Universities of Central South University(Grant No.2018zzts031).
文摘To explore the influence of spatially varying ground motion on the dynamic behavior of a train passing through a three-tower cable-stayed bridge,a 3D train–track–bridge coupled model is established for accurately simulating the train–bridge interaction under earthquake excitation,which is made up of a vehicle model built by multi-body dynamics,a track–bridge finite element model,and a 3D rolling wheel–rail contact model.A conditional simulation method,which takes into consideration the wave passage effect,incoherence effect,and site-response effect,is adopted to simulate the spatially varying ground motion under different soil conditions.The multi-time-step method previously proposed by the authors is also adopted to improve computational efficiency.The dynamic responses of the train running on a three-tower cablestayed bridge are calculated with differing earthquake excitations and train speeds.The results indicate that(1)the earthquake excitation significantly increases the responses of the train–bridge system,but at a design speed,all the running safety indices meet the code requirements;(2)the incoherence and site-response effects should also be considered in the seismic analysis for long-span bridges though there is no fixed pattern for determining their influences;(3)different train speeds that vary the vibration characteristics of the train–bridge system affect the vibration frequencies of the car body and bridge.
基金partially provided by a Discovery Grant (No.1028495) and Accelerator Award (No.1030390) through the Natural Sciences and Engineering Research Council of Canada (NSERC)the Faculty of Kinesiology Dean's Doctoral Studentship Program at the University of Calgary
文摘Background: Running-related overuse injuries can result from the combination of extrinsic(e.g., running mileage) and intrinsic risk factors(e.g.,biomechanics and gender), but the relationship between these factors is not folly understood. Therefore, the first purpose of this study was to determine whether we could classify higher-and lower-mileage runners according to differences in lower extremity kinematics during the stance and swing phases of running gait. I he second purpose was to subgroup the runners by gender and determine whether we could classify higherand lower-mileage runners in male and female subgroups.Methods: Participants were allocated to the "higher-mileage" group(≥32 km/week; n= 41(30 females)) or to the "lower-mileage" group(≤25 km;n= 40(29 females)). Three-dimensional kinematic data were collected during 60 s of treadmill running at a self-selected speed(2.61 ± 0.23 m/s).A support vector machine classifier identified kinematic differences between higher-and lower-mileage groups based on principal component scores.Results: Higher-and lower-mileage runners(both genders) could be separated with 92.59% classification accuracy. When subgrouping by gender,higher-and lower-mileage female runners could be separated with 89.83% classification accuracy, and higher-and lower-mileage male runners could be separated with 100% classification accuracy.Conclusion: These results demonstrate there are distinct kinematic differences between subgroups related to both mileage and gender, and that these factors need to be considered in future research.
基金supported by General Research Funds granted by the Hong Kong Research Grant Council(#Poly U152065/17E)funding from the National Natural Science Foundation of China(#11732015)。
文摘Background:Segment coordination variability(CV)is a movement pattern associated with running-related injuries.It can also be adversely affected by a prolonged run.However,research on this topic is currently limited.The purpose of this study was to investigate the effects of a prolonged run on segment CV and vertical loading rates during a treadmill half marathon.Methods:Fifteen healthy runners ran a half marathon on an instrumental treadmill in a biomechanical laboratory.Synchronized kinematic and kinetic data were collected every 2 km(from 2 km until 20 km),and the data were processed by musculoskeletal modeling.Segment CVs were computed from the angle-angle plots of selected pelvis-thigh,thigh-shank,and shank-rearfoot couplings using a modified vector coding technique.The loading rate of vertical ground reaction force was also calculated.A one-way MANOVA with repeated measures was performed on each of the outcome variables to examine the main effect of running mileage.Results:Significant effects of running mileage were found on segment CVs(p≤0.010)but not on loading rate(p=0.881).Notably,during the early stance phase,the CV of pelvis frontal thigh frontal was significantly increased at 20 km compared with the CV at 8 km(g=0.59,p=0.022).The CV of shank transverse vs.rearfoot frontal decreased from 2 km to 8 km(g=0.30,p=0.020)but then significantly increased at both 18 km(g=0.05,p<0.001)and 20 km(g=0.36,p<0.001).Conclusion:At the early stance,runners maintained stable CVs on the sagittal plane,which could explain the unchanged loading rate throughout the half marathon.However,increased CVs on the frontal/transverse plane may be an early sign of fatigue and indicative of possible injury risk.Further studies are necessary for conclusive statements in this regard.
文摘Running related foot injuries are associated with excessive foot movements due to malaligned foot structure and poor functional foot stability. Clinicians tape the foot to alleviate pain and prevent further injuries, whilst allowing the athlete to continue training. However, the effect of taping is not conclusive. The purpose of this study is to investigate if taping effectively improves foot structure, functional foot stability and reduces excessive foot movements during running. Twenty-two subjects had their foot structure identified as： fiat foot stable, fiat foot unstable and normal arched unstable according to the FPI （foot posture index） and the Modified Romberg＇s Test with the BESS （balance error scoring system） criteria. The subjects ran on an instrumented treadmill barefooted with their feet taped and untaped. Running kinetic and kinematic data were collected and analysed using a paired t-test and 3x2 ANOVA. Taping improved foot structure but not functional foot stability. During running, taping significantly reduced rearfoot eversion. Taping increased the loading rate in the fiat foot and normal arched unstable groups but reduced the loading rate for the flat foot stable group. Implication on the appropriate use of foot taping was discussed.
文摘为研究跑步运动中不同紧度护膝对膝关节防护效果的影响,以20名热爱跑步运动的健康女性作为实验对象,运用三维动态捕捉技术捕捉测试者佩戴不同紧度护膝在不同速度跑步下的膝关节三维角度数据,将实验数据进行相关数理统计分析与研究。从紧身压迫角度出发对跑步过程中膝关节三维角度进行探讨,为紧身运动护膝的开发研究提供理论指导。结果表明:紧身压迫是衡量膝关节固定效果的一个重要因素,施加表面防护载荷对膝关节起到了一定的固定束缚作用;护膝紧身压迫应控制在2.152 8~2.861 7 k Pa内,以满足运动过程中对膝关节的固定保护作用。该研究为运动防护装备开发提供了设计依据。
