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 A...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.展开更多
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. Howev...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.展开更多
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...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.展开更多
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 ...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.展开更多
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) pa...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.展开更多
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...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.展开更多
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 unde...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.展开更多
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...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。展开更多
基金supported by the Grant-in-Aid for Young Scientists(B)Project(Grant No.24700716)funded by the Ministry of Education,Culture,Sports,Science and Technology,Japan.
文摘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.
基金The author gratefully acknowledges the financial support and affiliation from the University of Adelaide.
文摘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.
基金the Spanish Ministry of Science and Technology for fnancial support awarded under Contract Reference Numbers BIA2009-09673 and MTM2010-21235-C02-02
文摘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.
基金supported by the National Natural Science Foundation of China (10702048 and 11102126)Natural Science Foundation of Shanxi (2010021004-1)
文摘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.
文摘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.
文摘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.
文摘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.
文摘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。
