The deterministic condition for the ground reaction force acting point on the combined knee valgus and tibial internal rotation moments in early phase of cutting maneuvers in female athletes

Background:Combined knee valgus and tibial internal rotation(VL+IR)moments have been shown to stress the anterior cruciate ligament(ACL)in several in vitro cadaveric studies.To utilize this knowledge for non-contact ACL injury prevention in sports,it is necessary to elucidate how the ground reaction force(GRF)acting point(center of pressure(CoP))in the stance foot produces combined knee VL+IR moments in risky maneuvers,such as cuttings.However,the effects of the GRF acting point on the development of the combined knee VL+IR moment in cutting are still unknown.Methods:We first established the deterministic mechanical condition that the CoP position relative to the tibial rotational axis differentiates the GRF vector’s directional probability for developing the combined knee VL+IR moment,and theoretically predicted that when the CoP is posterior to the tibial rotational axis,the GRF vector is more likely to produce the combined knee VL+IR moment than when the CoP is anterior to the tibial rotational axis.Then,we tested a stochastic aspect of our theory in a lab-controlled in vivo experiment.Fourteen females performed 60˚cutting under forefoot/rearfoot strike conditions(10 trials each).The positions of lower limb markers and GRF data were measured,and the knee moment due to GRF vector was calculated.The trials were divided into anterior-and posterior-CoP groups depending on the CoP position relative to the tibial rotational axis at each 10 ms interval from 0 to 100 ms after foot strike,and the occurrence rate of the combined knee VL+IR moment was compared between trial groups.Results:The posterior-CoP group showed significantly higher occurrence rates of the combined knee VL+IR moment(maximum of 82.8%)at every time point than those of the anterior-CoP trials,as theoretically predicted by the deterministic mechanical condition.Conclusion:The rearfoot strikes inducing the posterior CoP should be avoided to reduce the risk of non-contact ACL injury associated with the combined knee VL+IR stress.

Abnormal ground reaction forces lead to a general decline in gait speed in knee osteoarthritis patients

AIM To analyse ground reaction forces at higher speeds using another method to be more sensitive in assessing significant gait abnormalities. METHODS A total of 44 subjects, consisting of 24 knee osteoarthritis(OA) patients and 20 healthy controls were analysed. The knee OA patients were recruited from an orthopaedic clinic that were awaiting knee replacement. All subjects had their gait patterns during stance phase at top walking speed assessed on a validated treadmill instrumented with tandem force plates. Temporal measurements and ground reaction forces(GRFs) along with a novel impulse technique were collected for both limbs and a symmetry ratio was applied to all variables to assess inter-limb asymmetry. All continuous variables for each group were compared using a student t-test and χ2 analysis for categorical variables with significance set at α = 0.05. Receiver operator characteristics curves were utilised to determine best discriminating ability.RESULTS The knee OA patients were older(66 ± 7 years vs 53 ± 9 years, P = 0.01) and heavier(body mass index: 31 ± 6 vs 23 ± 7, P < 0.001) but had a similar gender ratio when compared to the control group. Knee OA patients were predictably slower at top walking speed(1.37 ± 0.23 m/s vs 2.00 ± 0.20 m/s, P < 0.0001) with shorter mean step length(79 ± 12 cm vs 99 ± 8 cm, P < 0.0001) and broader gait width(14 ± 5 cm vs 11 ± 3 cm, P = 0.015) than controls without any known lower-limb joint disease. At a matched mean speed(1.37 ± 0.23 vs 1.34 ± 0.07), ground reaction results revealed that pushoff forces and impulse were significantly(P < 0.0001) worse(18% and 12% respectively) for the knee OA patients when compared to the controls. Receiver operating characteristic curves analysis demonstrated total impulse to be the best discriminator of asymmetry, with an area under the curve of 0.902, with a cut-off of-3% and a specificity of 95% and sensitivity of 88%.CONCLUSION Abnormal GRFs in knee osteoarthritis are clearly evident at higher speeds. Analysing GRFs with another method may explain the general decline in knee OA patient's gait.

Confining stress effect on the elastoplastic ground reaction considering the Lode angle dependence

The convergence confinement methods are solutions employed to estimate convergence in circular tunnels. They are mostly based on constitutive equations governed by the Mohr-Coulomb and Hoek-Brown yield criteria. However, the solutions based on these criteria neglect the intermediate principal stress confining effect on the ground reaction estimation. Therefore, in this paper, a Drucker-Prager yield criterion governed solution integrated with the Lode angle parameter is employed. It considers the intermediate principal stress influence and the critical effect of the parameter on failure characterization.Subsequently, it is verified with results attained from numerical simulations which consider an elasticperfectly plastic constitutive law with a non-associative flow rule within FLAC3D. It was drawn from the results that the ground reaction and plastic evolution are influenced by the confining stress.Furthermore, considering a suitable yield criterion leads to realistic convergence and plastic evolution estimation. The circumscribed DP criterion governed solution with Lode angle parameter value(0.8) is considered appropriate for the realistic ground reaction estimation in the three-dimensional(3D) stress state rock mass. It estimates approximately 3.4% of tunnel convergence as compared to the classic solutions(5%) and plastic radius estimated to be approximately 2.45 m compared to 2.84 m.

Ground reaction curves for circular excavations in non-homogeneous,axisymmetric strain-softening rock masses

Fast methods to solve the unloading problem of a cylindrical cavity or tunnel excavated in elasto-perfectly plastic, elasto-brittle or strain-softening materials under a hydrostatic stress feld can be derived based on the self-similarity of the solution. As a consequence, they only apply when the rock mass is homogeneous and so exclude many cases of practical interest. We describe a robust and fast numerical technique that solves the tunnel unloading problem and estimates the ground reaction curve for a cylindrical cavity excavated in a rock mass with properties depending on the radial coordinate, where the solution is no longer self-similar. The solution is based on a continuation-like approach(associated with the unloading and with the incremental formulation of the elasto-plastic behavior), fnite element spatial discretization and a combination of explicit sub-stepping schemes and implicit techniques to integrate the constitutive law, so as to tackle the diffculties associated with both strong strain-softening and elasto-brittle behaviors. The developed algorithm is used for two practical ground reaction curve computation applications. The frst application refers to a tunnel surrounded by an aureole of material damaged by blasting and the second to a tunnel surrounded by a ring-like zone of reinforced(rock-bolted) material.

Reduction in ground reaction force variables with instructed barefoot running

Backgound:Barefoot(BF) running has recently increased in popularity with claims that it is more natural and may result in fewer injuries due to a reduction in impact loading.However,novice BF runners do not necessarily immediately switch to a forefoot strike pattern.This may increase mechanical parameters such as loading rate,which has heen associated with certain running-related injuries,specifically,tibial stress fractures.patellofemoral pain,and plantar iasciitis.The purpose of this study was to examine changes in loading parameters between typical shod running and instructed BF running with real-time force feedback.Methods:Forty-nine patients seeking treatment for a lower extremity injury ran on a force-sensing treadmill in their typical shod condition and then BF at the same speed.While BF they received verbal instruction and real-time feedback of vertical ground reaction forces.Results:While 92%of subjects(n = 45) demonstrated a rearfoot strike pattern when shod,only 2%(n = 1) did during the instructed BF run.Additionally,while BF 47%(n = 23) eliminated the vertical impact transient in all eight steps analyzed.All loading variables of interest were significantly reduced from the shod to instructed BF condition.These included maximum instantaneous and average vertical loading rates of the ground reaction force(p 【 0.0001),stiffness during initial loading(p 【 0.0001).and peak medial(p = 0.001) and lateral(p 【 0.0001) ground reaction forces and impulses in the vertical(p 【 0.0001).medial(p = 0.047),and lateral(p 【 0.0001) directions.Conclusion:As impact loading has been associated with certain running-related injuries,instruction and feedback on the proper forefoot strike pattern may help reduce the injury risk associated with transitioning to BF running.

Analysis of kinematic data and determination of ground reaction force of foot in slow squat

In the present paper, the ground reaction force （GRF） acting on foot in slow squat was determined through a force measuring system, and at the same time, the kinematic data of human squat were obtained by analyzing the photographed image sequences. According to the height and body weight, six healthy volunteers were selected, three men in one group and the other three women in another group, and the fundamental parameters of subjects were recorded, including body weight, height and age, etc. Based on the anatomy characteristics, some markers were placed on the right side of joints. While the subject squatted at slow speed on the force platform, the ground reaction forces on the forefoot and heel for each foot were obtained through calibrated force platform. The analysis results show that the reaction force on heel is greater than that on forefoot, and double feet have nearly constant force. Moreover, from processing and analyzing the synchronously photographed image sequences in squat, the kinematic data of human squat were acquired, including mainly the curves of angle, angular velocity and angular acceleration varied with time for knee, hip and ankle joints in a sagittal plane. The obtained results can offer instructive reference for photographing and analyzing the movements of human bodies, diagnosing some diseases, and establishing in the future appropriate mathematical models for the human motion.

A New Method of Desired Gait Synthesis for Biped Walking Robot Based on Ground Reaction Force

A new method of desired gait synthesis for biped walking robot based on the ground reaction force was proposed. The relation between the ground reaction force and joint motion is derived using the D’Almbert principle. In view of dynamic walking with high stability, the ZMP(Zero Moment Point)stability criterion must be considered in the desired gait synthesis. After that, the joint trajectories of biped walking robot are decided by substituting the ground reaction force into the aforesaid relation based on the ZMP criterion. The trajectory of desired ZMP is determined by a fuzzy logic based upon the body posture of biped walking robot. The proposed scheme is simulated and experimented on a 10 degree of freedom biped walking robot. The results indicate that the proposed method is feasible.

Gait-Ground Reaction Force Sensors Selection Based on ROC Curve Evaluation

Classification of normal gait from pathological gait as then can be used as indicator of falling among subjects requires the correct choice of sensor location in the insole. Such a flexi force- sensor can be used underneath foot to measure vertical ground reaction force. To start with, the most relevant information (parameters) that can characterize the recorded signals are extracted from the vertical ground reaction force signals. Then Receiver Operating Characteristic curve is used to evaluate the features upon 8 sensors underneath each foot located at different locations. To confirm results obtained, features are passed upon a chosen classifier, in this paper K-nearest neighbors algorithm is chosen. Results show that the sensor located at the inner arch of the sole of the foot (i.e. at the mid foot) holds the most relevant information needed for better classification compared to other sensors.

A Guide to the Influence of Ground Reaction on Ship Stability

Grounded ship faces up exceptionally different stability forces unlike in her normal operating condition. This critical situation must be corrected as soon as can minimize hull stress, the risk of pollution and stability failure. Re-floating the ship need full understanding of the impact of ground reaction （R） on the ship buoyancy and stability. Re-floating the ship has different phases and there are several immediate actions that should be taken by ship＇s crew; one of these phases is re-calculation of ship stability conditions. In this paper, a guide to understanding the effect of the ground reaction （R）, determines the amount of ground pressure and its location. With consideration of the seabed form whether symmetric of asymmetric. Calculating the magnitude of the ground reaction （R） using different applicable methods, explaining the effect of using weight to re-float the ship by her own means, focusing on GM calculation after grounding.

Compatibility of the Support System Consisting of Yielding Elements and Shotcrete Lining in Highly Faulted Grounds

The design procedure is made for a mine shaft where permanent underground facilities are interconnected. The highly faulted grounds were identified using empirical and semi-empirical theories. Furthermore, the behavior types are presented. This paper presents excavation and support methods in such ground conditions and the calculations results show that the installation of the yielding elements have an effect on support elements and prevent shotcrete damage during the curing stage. Different numerical analyses carried out showed that, with the yielding elements installed, the total displacements increase but the final axial force reduces, and therefore, the characteristic compressive strength of shotcrete is not exceeded. The calculation results of ground loads and displacements on the designed support system are presented with a 3D numerical geo-mechanical model adopted for highly faulted ground surrounding deeper complex underground structures.

低压浸渗法制备Gr（C）／Mg复合材料

对用低压浸渗法制备石墨（碳）长纤维镁基复合材料进行了研究。结果表明，制备工艺条件对复合状况、界面反应及复合材料性能均有明显影响。通过纤维表面ＳｉＯ２涂层处理和优化浸渗工艺，可成功地制备出高性能的复合材料，拉伸断裂强度可达５０９ＭＰａ，模量亦可达１４２ＧＰａ。

碘催化Grebke反应合成3-氨基咪唑并[1,2-a]吡啶衍生物

以芳香醛、2-氨基吡啶和异腈为原料,10 mol%分子碘作催化剂,甲醇作溶剂,回流反应3 h合成标题化合物。该反应条件温和,产率为76%~90%,相应的结构经过红外、核磁共振和质谱表征确认。

Fe3O4羧甲基纤维素钠包覆量对酸性大红GR降解影响的研究

在不同浓度羧甲基纤维素钠溶液中以共沉淀法制备得到1号、2号和3号Fe3O4/CMC纳米复合物，将所制得的产物通过傅里叶红外吸收光谱（FT—IR）、X射线衍射仪（XRD）、扫描电子显微镜（SEM）等仪器进行分析，制备的3号Fe3O4/CMC纳米复合物是粒径为50nm左右的尖晶石型复合材料，并证实了羧甲基纤维素钠成功包覆了Fe3O4纳米粒子，新制备的Fe3O4/CMC纳米复合材料不仅具有良好的磁性能，而且还具有良好的分散性能。使用Fe3O4/CMC复合纳米材料为催化剂对酸性大红GR进行了类芬顿（Fenton）氧化降解研究，在相同反应条件下。3号Fe3O4/CMC纳米催化剂在非均相类芬顿体系中对偶氮染料酸性大红GR的降解率优于1号、2号Fe3O4/CMC纳米催化剂，在pH=3．5的条件下，6h后降解率高达98％以上。

单侧负重对足底压力和稳定性的影响研究

单手提重物在日常生活和工作中很常见,不对称负重不仅增大下肢载荷,而且使人-手提物重心偏离正中矢状面,可能导致足底水泡、应力性骨折和摔跤风险增大。用1 m的压力板测量了15名健康男性大学生分别手提7 kg和14 kg重的包行走时的垂直地面反作用力和足底压力中心,用1 m的测力台测量静止站立30 s时的地面反作用力,以此为依据分析单侧负重对人体稳定性、足部冲击和步态的影响。结果表明,在实验的两种负重时,足底压力绝对值增大,相对值不变,稳定性降低,步态改变。针对经常性单侧负重群体的功能鞋设计,需要增大鞋底缓冲性能以减小损伤,增加鞋类稳定性以减小摔跤风险。

基于统一强度理论的扰损围岩巷道脆塑性解答

钻爆法施工常造成岩质巷道扰损区围岩性能劣化。针对扰损围岩、扰损外围岩的弹塑性状态下不同的扰损围岩巷道力学模型,采用统一强度理论、弹-脆-塑性模型和非关联流动法则,建立扰损围岩巷道有关应力、位移和塑性区半径的脆塑性解答,探讨巷道力学模型的转换路径及判定方法,并将结果进行对比、验证,获得各因素的影响规律。研究表明:提出的巷道脆塑性解答合理反映了中间主应力、围岩扰损范围和峰后强度、剪胀特性的综合影响,通过参数组合变换可退化为多种解答并得到正确性验证,具有重要的理论意义和应用前景;巷道力学模型判定与中间主应力、围岩扰损范围密切相关,显著影响巷道应力-位移分布和围岩特征曲线;支护压力和巷道稳定变形随着围岩峰后强度下降、剪胀特性参数增加而明显增大。

山地户外运动鞋对人体下肢落地冲击的影响研究

为探讨山地户外运动鞋对人体下肢落地冲击的影响,以光学三维动态捕捉系统与Kistler三维测力台实时采集并对比被试者穿着高缓震户外运动鞋与无缓震户外运动鞋完成山地户外运动常见落地动作时下肢的地面反作用力数据与下肢关节运动学参数。结果发现,穿着高缓震户外运动鞋与无缓震户外运动鞋落地时,人体下肢地面反作用力存在显著性差异:穿着高缓震户外运动鞋时下肢落地的地面反作用更小,对下肢的冲击与损伤更小;穿着高缓震户外运动鞋与无缓震户外运动鞋落地时人体下肢关节的活动度、触地角度、最小角度、最大角速度、出现时间均不存在显著性差异,但穿着无缓震户外运动鞋时下肢关节的活动度小于高缓震户外运动鞋,表明穿着无缓震户外运动鞋落地时下肢的损伤风险更大。

偏瘫患者下台阶过程下肢生物力学特征分析

目的对比分析偏瘫患者以不同方式下台阶过程中下肢生物力学特征,为降低患者下台阶过程中的跌倒风险提供理论依据。方法选取10名正常人和20名符合要求的偏瘫患者,使用Qualisys动作捕捉系统和Kistler三维测力台对受试者下台阶过程中的运动学和动力学数据进行收集,分析其在下台阶过程中的生物力学特征和跌倒风险。结果相较于正常人和先用健足下台阶(steps on the healthy side,SHS),先用患足下台阶(steps on the affected side,SAS)时,患侧下肢各关节屈伸活动幅度较小;SHS降低了健侧膝关节屈伸活动幅度,患侧下肢各关节屈伸活动幅度较SAS大;SAS下台阶左右方向地面反作用力(ground reaction force,GRF)曲线变化与正常人较为一致,患侧落地瞬间垂直GRF最大为1.05倍体重,健侧为1.25倍体重,低于正常人(1.5倍体重);SHS下台阶健侧落地瞬间最大垂直GRF为1.85倍体重,高于SAS和正常人。结论相较于SAS,患者使用SHS下台阶患侧关节活动幅度和落地瞬间垂直GRF较大,更难掌握。SAS更符合偏瘫患者下台阶的生物力学特征。

基于神经网络以全身关节点坐标估算侧切变向动作下肢动力学参数

目的:应用神经网络模型以人体关节点坐标为输入变量,估算运动员侧切变向动作过程中地面反作用力与下肢关节力矩。方法:采用Motion红外高速动作捕捉系统和Kistler三维测力台同步采集71名男子足球运动员完成侧切动作过程中的运动学和动力学数据。建立神经网络模型,以人体18个关节点坐标作为输入变量估算髋、膝、踝关节力矩和地面反作用力。采用相关系数、均方根误差及其标准化值评价神经网络估算效度;采用统计参数映射分析神经网络估算与实际曲线之间的差异;采用配对样本t检验分析神经网络估算所得地面反作用力峰值与实际值之间的差异。结果:神经网络估算的动力学参数与实测值之间具有较好相关性(r=0.82~0.97)。神经网络估算所得动力学参数在各个方向上的误差具有显著差异(P<0.050),矢状面具有较大的相关系数以及较小的标准化均方根误差。估算的侧切动作支撑阶段动力学指标曲线仅在地面反作用力前后分量(10%~12%,P=0.011;93%~95%,P=0.015)和垂直分量(5%~15%,P<0.001)以及髋关节内外翻力矩(99%~100%,P=0.015)和内外旋力矩(1%,P=0.017)的很少部分与实际曲线之间具有显著差异。神经网络估算所得的3个方向地面反作用力峰值与实测值之间均无显著差异。结论:应用神经网络模型以全身关节点坐标估算的运动员侧切变向动作过程中下肢关节力矩和地面反作用力与实测值之间相关性高,误差较小,其中矢状面效果最好。建立的神经网络模型可用于非实验室环境下监控侧切变向动作中的损伤风险。

跆拳道运动员后踢动作时下肢双侧生物力学差异性

探讨跆拳道后踢技术动作时下肢优势侧和非优势侧的运动生物力学特征,对影响后踢技术完成率的影响因素进行分析。采用VICON三维动作捕捉系统和KISTLER三维测力台同步采集12名武汉体育学院优秀跆拳道运动员完成后踢动作下肢的运动学和动力学数据,采用配对样本T检验分析后踢动作优势侧和非优势侧之间的差异。结果表明:进攻腿髋关节屈曲力矩峰值(P=0.000)、功率峰值(P=0.006)非优势侧大于优势侧,外展最大角速度(P=0.014)优势侧大于非优势侧;支撑腿髋关节屈曲最大角速度(P=0.001)、伸展功率峰值(P=0.037)优势侧大于非优势侧,屈曲力矩峰值(P=0.022)非优势侧大于优势侧。进攻腿膝关节屈曲最大角度(P=0.003)、伸展功率峰值(P=0.044)优势侧大于非优势侧;支撑腿膝关节屈曲最大角度(P=0.006)、角速度(P=0.018)优势侧大于非优势侧,伸展最大角速度(P=0.022)非优势侧大于优势侧。支撑腿踝关节跖屈最大角速度(P=0.005)、功率峰值(P=0.035)、力矩峰值(P=0.005)优势侧大于非优势侧。进攻腿击打速度(P=0.002)、电子护具力度值(P=0.015)优势侧大于非优势侧。可见在提膝阶段,优势侧提膝时间更短,优势侧踝关节跖屈和非优势侧屈髋产生的能量输出更多;在踢击阶段,优势侧伸髋和伸膝的功率峰值较大,能有效提高击打速度;优势侧击打速度和击打力度值大于非优势侧,选择优势侧踢击可以提高后踢技术得分成功率。

不同等级男子撑竿跳高运动员助跑及起跳的生物力学特征研究

目的对不同等级男子撑竿跳高运动员质心速度、质心高度、地面反作用力和下肢关节力矩等生物力学指标的具体表现进行探讨,试图了解不同等级运动员的整体特征,并发现高水平运动员助跑及起跳过渡衔接的特点。方法使用大范围的三维动作捕捉系统以及3块测力台对优秀男子撑竿跳高运动员的运动学(200 Hz)和地面反作用力(2000 Hz)数据进行采集,分析比较了5名一级运动员、4名运动健将和3名国际级运动健将的生物力学指标。对国际级运动健将组、运动健将组和一级运动员组的同一生物力学指标两两之间采用非参数独立样本曼-惠特尼U单侧检验,对所有运动员倒2步、倒1步和起跳相应的生物力学指标两两之间采用非参数配对样本Wilcoxon符号秩单侧检验。结果不同等级撑竿跳高运动员助跑后两步和起跳的质心速度、质心高度、地面反作用力和下肢关节力矩等生物力学指标有显著性差异;倒2步、倒1步、起跳相应的生物力学指标之间有显著性差异。结论基于本研究的数据,男子撑竿跳高运动员表现出随等级而变化的生物力学特点,国际级健将运动员的质心速度、地面反作用力等指标体现了其较高的运动能力。倒2步、倒1步和起跳的质心速度、质心高度和地面反作用力等相应生物力学指标的显著差异反映了撑竿跳高技术动作的衔接特征,体现了撑竿跳高助跑向起跳过渡的运动学和动力学特点。