足弓刚度对纵跳动作的下肢生物力学影响

目的：通过对比跳高运动员足弓刚度对单腿纵跳成绩的影响,为跳高运动员选材及专项训练提供理论依据。方法：招募15名男性国家二级跳高运动员,对受试者足部形态进行红外光学扫描,采用红外运动捕捉系统和测力台同步采集受试者纵跳动作的下肢运动学和动力学数据。结果：在纵跳表现中,足弓刚度与地面反作用力峰值间存在线性关系,高刚度足弓受试者的峰值vGRF显著大于低刚度足弓的受试者(P<0.05),高刚度足弓组冲击加载率为15.2BW/s±1.8BW/s,低刚度足弓组地面反作用力加载率为12.3BW/s±0.9BW/s,且存在显著差异(P<0.05)。同时,高刚度足弓组的峰值vGRF时刻踝屈角度(21.24°±4.4°)显著性高于低刚度足弓组的峰值vGRF时刻踝屈角度(24.43°±3.6°),P<0.05。结论：在优秀跳高运动员中,足弓刚度与纵跳过程中的踝膝关节屈伸角度、地面反作用力及加载率有显著影响,且与地面反作用力峰值间存在显著正向线性关系。因此,在跳跃类项目我们应该关注运动员足底肌肉力量训练。在描述跳跃过程中的足部及其生物力学特征时,使用静态足部分类值得纳入考量。     

短跑支撑阶段运动生物力学分析

采用测力、高速录像及特殊的数据平滑处理方法研究短跑运动员途中跑技术的运动学和动力学特征,进行田径技术原理的探索。结果表明,支撑时期可以分为着地阶段和蹬伸阶段,蹬伸阶段可分前蹬,后蹬前段,后蹬后段。途中跑前蹬段是人体重心垂直方向向上加速的重要时刻,前蹬时下肢一定程度的垂直加速用力虽影响水平速度,但对提高垂直速度有积极意义,前蹬和后蹬前段是身体重心垂直向上加速运动的阶段。着地缓冲后的前蹬用力也是实现良好成绩的技术之一。途中跑着地和前蹬阶段失去的水平速度损失完全可以从后蹬中得到补充。着地点过近对前支撑阶段获得重要的垂直速度不利,支撑阶段离地前的20ms身体重心速度已经开始下降。     

跑与纵跳关节功率的研究

采用运动生物力学方法考察了跑与纵跳的关节功率及其与人体疲劳的关系。跑的数据是借鉴国外一些研究的资料；纵跳，分别在功率自行车上蹬踏30s之前和之后进行，动作用摄像机摄录下来，并在运动解析仪上加以分析。纵跳中的地面反作用力用三维测力台测量。利用上述系统的数据计算了关节功率。通过比较两组数据计算了各关节功率的变化，从而得到了对人体疲劳的一种定量描述。从而得知：在跑中当脚着地后，首先是髋关节处于屈的状态，其关节功率达到最大值；其次是踝关节屈的关节功率变化较大；最后是膝关节功率达到最大值。其中踝关节变化最大。在腾空状态中，髋关节与膝关节的关节功率处于较大值，并且变化较大。纵跳过程中，疲劳主要表现为膝关节功率的下降。     

乒乓球运动员正手弧圈球技术的地面支撑作用力分析

运用两块瑞士产 KISTLER 三维测力台对10名优秀男乒乓球运动员正手拉弧圈球技术过程中地面对人体的地面支撑反作用力进行测试.用两种发力方式拉弧圈球,一为用最大力量,二为中等力量.从垂直、水平、前后3个方向对完成轻拉和重拉时左右脚地面支撑反作用力的生物力学特征进行了描述,并对两种技术动作之间左右脚支反力的最大力值进行了对比分析,得出:(1)完成轻拉和重拉时,垂直方向上的地面支撑反作用力最大.左右和前后方向上的支反力较小;身体重心的移动影响地面支撑反作用力的变化,两者之间有密切联系.(2)发力拉弧圈球时,更要注重增加左右方向和前后方向上的蹬地力和重心移动幅度.     

落地高度对高水平短跑运动员跳深动作下肢生物力学和反应性力量的影响

目的:检查落地高度对高水平短跑运动员跳深动作下肢生物力学和反应性力量的影响并进一步确定下肢生物力学指标与反应性力量指标之间的关联性以及跳深动作的最佳负荷高度。方法:14名男子高水平短跑运动员参与四种落地高度下(0.15m、0.30m、0.45m和0.60m)的跳深动作测试。6台红外高速摄像机和2块三维测力台同步采集跳深动作的运动学和地面反作用力信号。结果:落地高度显著影响跳深动作的碰撞力和蹬伸阶段的垂直地面反作用力峰值(p=0.000和0.039),髋关节伸力矩(p=0.038)、踝关节跖屈力矩(p=0.030)和下肢支撑力矩(p=0.010),髋、膝和踝关节离心功率(p均为0.000),平均功率输出(p=0.009),反应力量指数(p=0.006)和反应力量比(p=0.029);落地高度与平均功率输出显著相关,最佳负荷高度为0.465m(R~2=0.117,p=0.037);蹬伸阶段的垂直地面反作用力峰值(r=0.816,p=0.000;r=0.927,p=0.000)和平均功率输出(r=0.961,p=0.000;r=0.770,p=0.000)与反应力量指数和反应力量比均显著相关。结论:落地高度显著影响跳深动作的下肢生物力学和反应性力量指标,蹬伸阶段垂直地面反作用力和平均功率输出与反应性力量指标均存在非常显著的相关性,在0.15m～0.60m的落地高度范围内存在实现跳深动作最大平均力学功率输出的最佳负荷高度。建议针对高水平短跑运动员跳深训练时应该根据个体运动员的最大平均功率输出、反应力量指数和反应力量比等指标确定最佳负荷高度,以实现最佳训练效果并预防运动损伤。     

助跑速度和性别对45度变向动作中下肢生物力学负荷的影响

目的:探究不同助跑速度下45°变向动作中男、女运动员下肢生物力学参数的变化情况。方法:运用三维红外高速摄像机和测力台对26名篮球运动员在不同助跑速度下45°变向动作中下肢生物力学运动学和动力学信号进行采集。运用Visual-3D分析软件对采集的信号进行处理并计算相关生物力学参数。结果:男、女运动员在快速助跑下足与地面接触时刻的膝关节外展角显著大于低速助跑(p<0.05)。快速助跑下男子运动员的最大膝关节外展角显著增加(p<0.05)。助跑速度显著影响男、女运动员的垂直地面反作用力、膝关节屈力矩和外展力矩参数(p<0.05)。女子运动员在膝关节屈角和最大膝关节外展角参数方面与男子运动员存在显著性差异(p<0.05)。快速助跑时女子运动员的垂直地面反作用力和膝关节屈力矩峰值均显著高于男子运动员(p<0.05)。中速助跑时,女子运动员的垂直地面反作用力峰值参数显著大于男子运动员(p<0.05)。结论:不同助跑速度对45°变向动作中男、女运动员部分下肢生物力学参数具有显著性影响。另外,同一助跑速度下部分下肢生物力学负荷参数也存在明显的性别差异性。     

高弓足和正常足在赤足行走过程中的力学特征分析

研究目的：观察高弓足和正常足在赤足行走过程中的运动学和动力学参数变化,分析高弓足易损伤的原因,为高弓足的康复治疗提供实验依据。研究方法：选取9名高弓足受试者为实验组,10名正常足受试者为对照组。利用Vicon-MX红外摄像系统进行动作捕捉,采集受试者常速行走时髋、膝、踝三大关节的运动学参数,同时利用KISTLER三维测力台采集行走过程中的足-地接触力。研究结果：在行走过程中,高弓足者髋关节在足趾离地时的外展角度小于正常足（P﹤0.05）;在垂直方向上的第二峰值地面反作用力（GRF）两组间差异存在统计学意义（P﹤0.05）,垂直方向的第一、第二峰值GRF和向后方向上的峰值GRF出现的时间均早于正常足（P﹤0.05）。结论：高弓足与正常足行走时所表现出的差异性可能是造成高弓足易损伤的原因,也反映了它们控制机制的不同。     

神经网络模型预测纵跳时下肢关节内力矩

关节肌肉力矩在生物力学研究中是一个非常有价值且应用性颇广的参数.要获得关节力矩数值,需同步测量运动学和地面反作用力参数,并通过逆向动力学(Inversce Dynamic)过程方能求得.目的在于建立推估两种纵跳:直立(Counter-Movement Jump,CMJ)和蹲位(Squat Jump,SJ)时下肢各关节力矩的人工神经网络(artificial ncural network,ANN),通过输入相对较容易测得的地面反作用力参数,推估下肢关节力矩(踝、膝、髋).以10位男性运动员为受试者,在测力台上完成两种纵跳,其所测得的地面反作用力参数作为神经网络模型的输入数据,以下肢各关节力矩为输出数据.经过网络优化后,所求得的最佳神经网络模型为"5-10-3模型"(即输入层有5个神经元;隐藏层为1层,有10个神经元;输出层有3个神经元).该模型所推估出的下肢各关节力矩极值相对误差均小于6%,与实测值的相关系数高达0.95以上,且在推估关节力矩曲线形态与角冲量方面的表现也十分良好,显示通过神经网络以地面反作用力来推估下肢各关节力矩的方法是准确和可行的.     

不同跳绳频率的运动训练研究

跳绳运动是体能训练之一,但是不同跳绳运动频率在运动训练的效益与人体健康的影响仍有待探讨。利用VICON动作捕捉系统及Kistler测力板撷取受过跳绳运动训练的15位小学生选手的下肢运动学资料及地面反作用力值,并采用重复量数单因子变异数分析检定三种频率跳绳运动各组间的跳跃高度及运动学参数是否有差异,统一显著水平定为α=．05,达显著时再用杜凯氏HSD法做事后比较。在探讨在跳绳运动训练过程中,进行低频组（60±2次／分钟）、中频组（100±2次／分钟）及高频组（140±2次／分钟）跳绳运动,下肢所受到相关力学参数的差异,以及下肢关节运动学变化及下肢劲度对着地策略的影响情形。研究结果表明,不同频率跳绳运动的垂直地面反作用力的最大值、被动冲量、负荷率、下肢劲度及角劲度值以高频组较高;不同频率跳绳运动的动作时间以低频组较多;下肢各关节角度变化量方面膝关节角度变化在中频组有突增现象（p〈05）。建议进行跳绳运动运动时,仍应注意高频率跳跃时垂直地面反作用力对人体的冲击。     

超等长阻力训练对下肢各关节角动力学的影响

为测试超等长阻力训练前后原地垂直纵跳动作下肢各关节角速度及角加速度,计算下肢各关节角刚度,观察超等长阻力训练对下肢各关节角动力学的影响。将16名青年男子篮球运动员随机分成超等长阻力训练组和常规训练对照组。采用VICON和三维测力台采集每个动作的运动学和动力学数据,计算下肢各关节角速度及角加速度,并经逆动力学方法计算下肢净关节力矩。结果可见,超等长阻力训练组髋、踝关节角速度和角刚度明显高于对照组,膝关节角速度及角刚度两组没有明显差异;超等长阻力训练组髋、膝、踝关节角加速度均显著高于对照组。结果说明超等长阻力训练可降低拉长-缩短周期支撑时间、缩短摊还期、增强肌肉-肌腱复合体能量转换能力、提高下肢肌肉爆发力。适于需要关节角速度、角加速度及爆发力的项目。     

Joint stiffness and running economy during imposed forefoot strike before and after a long run in rearfoot strike runners

Research has focused on the effects of acute strike pattern modifications on lower extremity joint stiffness and running economy (RE). Strike pattern modifications on running biomechanics have mostly been studied while runners complete short running bouts. This study examined the effects of an imposed forefoot strike (FFS) on RE and ankle and knee joint stiffness before and after a long run in habitual rearfoot strike (RFS) runners. Joint kinetics and RE were collected before and after a long run. Sagittal joint kinetics were computed from kinematic and ground reaction force data that were collected during over-ground running trials in 13 male runners. RE was measured during treadmill running. Knee flexion range of motion, knee extensor moment and ankle joint stiffness were lower while plantarflexor moment and knee joint stiffness were greater during imposed FFS compared with RFS. The long run did not influence the difference in ankle and knee joint stiffness between strike patterns. Runners were more economical during RFS than imposed FFS and RE was not influenced by the long run. These findings suggest that using a FFS pattern towards the end of a long run may not be mechanically or metabolically beneficial for well-trained male RFS runners.     

Sex differences in lower extremity stiffness and kinematics alterations during double-legged drop landings with changes in drop height

The aim of this study was to determine whether sex differences and effect of drop heights exist in stiffness alteration of the lower extremity during a landing task with a drop height increment. Twelve male participants and twelve female participants performed drop landings at two drop heights (DL40 and DL60; in cm). The leg and joint stiffnesses were calculated using a spring–mass model, and the joint angular kinematics were calculated using motion capture. Ground reaction forces (GRFs) were recorded using a force plate. The peak vertical GRF of the females was significantly increased when the drop height was raised from 40 to 60 cm. Significantly less leg and knee stiffness was observed for DL60 in females. The ankle, knee, and hip angular displacement during landing were significantly increased with drop height increment in both sexes. The knee and hip flexion angular velocities at contact were significantly greater for the 60 cm drop height relative to the 40 cm drop height in males. These sex disparities regarding the lower extremity stiffness and kinematics alterations during drop landing with a drop height increment would predispose females to lower extremity injury.     

Stiffness,intralimb coordination,and joint modulation during a continuous vertical jump test

This study analysed the modulation of jump performance, vertical stiffness as well as joint and intralimb coordination throughout a 30-s vertical jump test. Twenty male athletes performed the test on a force plate while undergoing kinematic analysis. Jump height, power output, ground contact time, vertical stiffness, maximum knee and hip flexion angles, and coordination by continuous relative phase (CRP) were analysed. Analysis of variance was used to compare variables within deciles, and t-tests were used to compare CRP data between the initial and final jumps. Results showed reduction in jump height, power output, and vertical stiffness, with an increase in contact time found during the test. Maximum knee and hip flexion angles declined, but hip angle decreased earlier (10–20% of the test) than knee angle (90–100%). No changes were observed in CRP for thigh–leg coupling when comparing initial and final jumps, but the trunk–thigh coupling was more in-phase near the end of the test. We conclude that fatigue causes reduction in jump performance, as well as changes in stiffness and joint angles. Furthermore, changes in intralimb coordination appear at the last 10% of the test, suggesting a neuromotor mechanism to counterbalance the loss of muscle strength.     

Can changes in midsole bending stiffness of shoes affect the onset of joint work redistribution during a prolonged run?

PurposeThis study aimed to investigate if changing the midsole bending stiffness of athletic footwear can affect the onset of lower limb joint work redistribution during a prolonged run.MethodsFifteen trained male runners (10-km time of <44 min) performed 10-km runs at 90% of their individual speed at lactate threshold (i.e., when change in lactate exceeded 1 mmol/L during an incremental running test) in a control and stiff shoe condition on 2 occasions. Lower limb joint kinematics and kinetics were measured using a motion capture system and a force-instrumented treadmill. Data were acquired every 500 m.ResultsProlonged running resulted in a redistribution of positive joint work from distal to proximal joints in both shoe conditions. Compared to the beginning of the run, less positive work was performed at the ankle (approximately 9%; p ≤ 0.001) and more positive work was performed at the knee joint (approximately 17%; p ≤ 0.001) at the end of the run. When running in the stiff shoe condition, the onset of joint work redistribution at the ankle and knee joints occurred at a later point during the run.ConclusionA delayed onset of joint work redistribution in the stiff condition may result in less activated muscle volume, because ankle plantar flexor muscles have shorter muscles fascicles and smaller cross-sectional areas compared to knee extensor muscles. Less active muscle volume could be related to previously reported decreases in metabolic cost when running in stiff footwear. These results contribute to the notion that footwear with increased stiffness likely results in reductions in metabolic cost by delaying joint work redistribution from distal to proximal joints.     

Ankle and knee kinetics between strike patterns at common training speeds in competitive male runners

The purpose of this study was to investigate the interaction of foot strike and common speeds on sagittal plane ankle and knee joint kinetics in competitive rear foot strike (RFS) runners when running with a RFS pattern and an imposed forefoot strike (FFS) pattern. Sixteen competitive habitual male RFS runners ran at two different speeds (i.e. 8 and 6?min?mile^?1) using their habitual RFS and an imposed FFS pattern. A repeated measures analysis of variance was used to assess a potential interaction between strike pattern and speed for selected ground reaction force (GRF) variables and, sagittal plane ankle and knee kinematic and kinetic variables. No foot strike and speed interaction was observed for any of the kinetic variables. Habitual RFS yielded a greater loading rate of the vertical GRF, peak ankle dorsiflexor moment, peak knee extensor moment, peak knee eccentric extensor power, peak dorsiflexion and sagittal plane knee range of motion compared to imposed FFS. Imposed FFS yielded greater maximum vertical GRF, peak ankle plantarflexor moment, peak ankle eccentric plantarflexor power and sagittal plane ankle ROM compared to habitual RFS. Consistent with previous literature, imposed FFS in habitual RFS reduces eccentric knee extensor and ankle dorsiflexor involvement but produce greater eccentric ankle plantarflexor action compared to RFS. These acute differences between strike patterns were independent of running speeds equivalent to typical easy and hard training runs in competitive male runners. Current findings along with previous literature suggest differences in lower extremity kinetics between habitual RFS and imposed FFS running are consistent among a variety of runner populations.     

Effects of cold water immersion on lower extremity joint biomechanics during running

The purpose of this study was to identify the influence of cryotherapy on lower extremity running biomechanics. Twenty-six healthy male volunteers were randomised into two intervention groups: cold water (cold water at ~11°C) or tepid water (tepid water at ~26°C). They were required to run at 4.0 ± 0.2 m · s^?1 before and after they underwent water immersion for 20 min. Differences between pre- and post-intervention were used to compare the influence of water intervention during running. Peak joint angles, peak joint moments, peak ground reaction forces (GRF) and contact time (CT) were calculated using three-dimensional gait analysis. Independent t-tests were applied with a significant alpha level set at 0.05. Decreased peak propulsive and vertical GRF, decreased plantarflexion moments, increased hip flexion angle and longer CT were observed following cold water immersion. Although cold water immersion (cryotherapy) affected the running movement, none of the alterations have been related to running biomechanical patterns associated with injuries. Therefore, our results indicated that cold water immersion appears safe prior to running activities.     

Contribution of the lower extremity joints to mechanical energy in running vertical jumps and running long jumps

The energy contribution of the lower extremity joints to vertical jumping and long jumping from a standing position has previously been investigated. However, the resultant joint moment contributions to vertical and long jumps performed with a running approach are unknown. metatarsophalangeal joint to these activities has not been investigated. The objective of this study was to determine the mechanical energy contributions of the hip, knee, ankle and metatarsophalangeal joints to running long jumps and running vertical jumps. A sagittal plane analysis was performed on five male university basketball players while performing running vertical jumps and four male long jumpers while performing running long jumps. The resultant joint moment and power patterns at the ankle, knee and hip were similar to those reported in the literature for standing jumps. It appears that the movement pattern of the jumps is not influenced by an increase in horizontal velocity before take-off. The metatarsophalangeal joint was a large energy absorber and generated only a minimal amount of energy at take-off. The ankle joint was the largest energy generator and absorber for both jumps; however, it played a smaller relative role during long jumping as the energy contribution of the hip increased.     

Acute fatigue negatively affects risk factors for injury in trained but not well-trained habitually shod runners when running barefoot

Introduction: Many factors may contribute to running-related injury. These include fatigue and footwear, the combination of which has rarely been studied, in particular with reference to barefoot running, recently advocated as a method to reduce injury risk. Methods: Twenty-two runners (12 well-trained and 10 trained) participated in a 10?km fatiguing trial. Knee and ankle joint kinematics and kinetics and electromyography were assessed during overground running in the barefoot and shod condition. This was performed pre- and post-fatigue using a motion capture system and force platforms. Results: Initial loading rate increased in the trained runners when barefoot but not shod. Shod knee stiffness increased in both groups after fatigue, whereas barefoot knee stiffness decreased only in the trained group. A reduction in barefoot bicep femoris pre-activation was found in both groups. During stance, a reduction in vastus lateralis and biceps femoris and an increase in tibialis anterior activity were found over time in both groups and conditions. Trained runners decreased gluteus medius and increased lateral gastrocnemius median frequency for both conditions after fatigue. Conclusion: When fatigued, gait adjustments in habitually shod runners may increase injury risk when running barefoot. Training status may be a risk factor for injury, as less-trained runners experience muscular fatigue changes that may compromise ground reaction force attenuation. Caution is recommended when transitioning to pure barefoot running.     

短跑途中跑支撑阶段支撑腿关节肌肉生物力学特性的研究

采用测力、测角加速度和多机多分辨拍摄技术对短跑途中跑支撑阶段肌肉动力学特征进行关节内力矩的计算与分析。研究表明，运动员踝关节跖屈肌的最大力矩与跑的速度呈显著相关；膝关节的伸肌在接近一半的支撑时间内是做离心收缩，离心收缩肌力矩的峰值要高于向心收缩的肌力矩峰值，离地前20％时刻膝关节屈肌起重要作用；髋关节在支撑阶段存在关节屈伸肌群交替工作，在着地后瞬间有较大的屈肌力矩，在离地前髋关节伸肌起重要作用，支撑阶段下肢关节肌肉快速退让性的离心收缩与主动收缩起同样重要的作用。     

Changes in running economy following downhill running

In this study, we examined the time course of changes in running economy following a 30-min downhill (-15%) run at 70% peak aerobic power (VO2peak). Ten young men performed level running at 65, 75, and 85% VO2peak (5 min for each intensity) before, immediately after, and 1 - 5 days after the downhill run, at which times oxygen consumption (VO2), minute ventilation, the respiratory exchange ratio (RER), heart rate, ratings of perceived exertion (RPE), and blood lactate concentration were measured. Stride length, stride frequency, and range of motion of the ankle, knee, and hip joints during the level runs were analysed using high-speed (120-Hz) video images. Downhill running induced reductions (7 - 21%, P < 0.05) in maximal isometric strength of the knee extensors, three- to six-fold increases in plasma creatine kinase activity and myoglobin concentration, and muscle soreness for 4 days after the downhill run. Oxygen consumption increased (4 - 7%, P < 0.05) immediately to 3 days after downhill running. There were also increases (P < 0.05) in heart rate, minute ventilation, RER, RPE, blood lactate concentration, and stride frequency, as well as reductions in stride length and range of motion of the ankle and knee. The results suggest that changes in running form and compromised muscle function due to muscle damage contribute to the reduction in running economy for 3 days after downhill running.