Minimal step length necessary for recovery of forward balance loss with a single step.

Although the boundary conditions necessary to trigger a step in reaction to a forward balance loss have been predicted in previous research, the relationship between minimal step length needed for balance recovery with this single step and the center of mass (COM) motion state (i.e., its position and velocity) remains unknown. The purpose of this paper was to present a theoretical framework within which the minimal step length needed for balance recovery can be estimated. We therefore developed a simplified four-segment sagittal model of human body stepping for balance recovery. The work-energy principle of the Newtonian mechanics was employed in the simulation to determine the amount of excess mechanical energy that can be absorbed as a function of step length and the corresponding eccentric joint work that can be generated in a single step. We found that an increase in initial forward velocity and a greater forward shift of the COM require a corresponding increase in the minimal step length needed for balance recovery. Furthermore, the minimal step length is also a function of the muscle strength at the ankle: the lower the muscle strength, the greater the minimal step length required. Our theoretical framework reduces the complexity associated with previous studies relying on forward dynamics and iterative optimization processes. This method may also be applied to study aspects of balance control such as the prevention of balance loss in the posterior or mediolateral direction.

The reaction strategy of lower extremity muscles when slips occur to individuals with trans-femoral amputation.

The aim of this study is to investigate the surface electromyography (sEMG) responses of lower extremity muscles for both healthy people and individuals with trans-femoral amputation (TFA), when slip events occur during level walking. Six male individuals with unilateral TFA and five healthy subjects participated in this study. Each subject was required to walk at a self-selected comfortable pace along a 5m plastic walkway, and to perform walking trials on dry and oily conditions respectively. The sEMG signals of muscles on legs and around waist were recorded in each trial and the normalized instantaneous muscle power (IMP) values were employed to quantify the response intensity. The IMP profiles of each muscle in oily-surface walking trials were compared quantitatively with that in dry-surface trials. There are three main findings in this study. (1) Different muscle reaction strategies are employed in slip events by the healthy persons and the individuals with TFA, respectively. Moreover, when the slip event occurs on the prosthetic leg and the intact leg of the individuals with TFA respectively, the muscle reaction strategies are also different. (2) The individuals with TFA face higher risks of fall than the healthy persons no mater slips occur on the prosthetic side or the intact side. (3) The hip muscles, especially the gluteus maximus (GMA) muscles, always enormously contribute to posture adjustment and balance recovery in slip events.

[The research advances of biomechanics of human knee joint ligaments].

Ligaments are the main parts which stabilize the knee joint. How to analog the ligaments in biomechanical model will affect the characteristics of the human knee dynamics and in the computation of the stress in ligaments between two bones. This symposium is aimed at the survey of the simplified method of the ligaments via mechanical parameters, and providing an exact method of constructing model.

[Synergic analysis and dynamics pattern of human normal gait during swing phase].

A dynamics model of human lower extremity, which combines musculotendon dynamics and muscle excitation-contraction dynamics, is presented. With this model, a motion process of normal gait during swing phase is numerically analyzed by use of the optimal control theory. The model was verified using experimental kinematics, muscles activation, and electromyographic data. The result showed that the tri-phasic activation pattern and synergistic muscles displayed during a normal gait in swing phase. The pattern consists of three distinct phases, i. e., acceleration during moving initiation, braking the moving segment, and posture control at the final specified position.

[Synergic pattern analysis of upper limb grasping movements].

In order to discuss the evaluation method of human upper limb movements, the patterns of movement coordination during healthy people prehension have been researched. Eight subjects were asked to perform different reaching-grasping and drinking water from the cup tasks with different indices of difficulty, and the arm movement trajectories and the main muscles group electromyography (EMG) data were collected. To explore the prehension control mechanism, a comparison has been made between the solution of the theoretic calculation and the experimental data. The results show that the topological invariance was observed in the trajectories of different task performance, and the linear relationships between joints covariation were exhibited. Moreover, the different muscles were controlled and combined into units of synergistic muscular group necessary to reach and grasp the goal.

The investigation on sEMG of lower extremity when a slip occurs in level walking.

The purpose of the present study was to determine the relationship between the surface electromyography (sEMG) variables and slip events using principal component analysis (PCA). Ten healthy young adults were required to walk on the oily surface on a self-selected comfortable pace. The sEMG signals of lower extremity muscles were recorded and analyzed, while kinematics data was recorded to assist slip definitions. When ten variables (seven in time domain and three in frequency domain) were considered in the PCA, the results indicated that 1) three most important principal components could explain more than 85% of the variation in the entire data set; 2) some variables should be especially noticed such as muscle power, the mean frequency, the median frequency and the amplitude amount exceeding the mean value.

[Quantitative gait evaluation using principal component analysis].

Evaluation of human gait function is of great significance in clinical medicine and rehabilitation engineering. A quantitative gait evaluation method using principal component analysis was proposed. The evaluation steps included that a series of characteristic index was performed by the gait parameters with a gait detection, and the index was normalized, quantified and summarized by principal component analysis. Then the evaluation results were shown in formulation, figures and tables. The examples showed that this system could evaluate the recovery of the gait by treatment.

Kinematic and dynamic performance of prosthetic knee joint using six-bar mechanism.

Six-bar linkages have been used in some prosthetic knees in the past years, but only a few publications have been written on the special functions of the mechanism as used in transfemoral prosthesis. This paper investigates the advantages of the mechanism as used in the prosthetic knee from the kinematic and dynamic points of view. Computer simulation and an experimental method were used in the investigation. The results show that the six-bar mechanism, as compared to the four-bar mechanism, can be designed to better achieve the expected trajectory of the ankle joint in swing phase. Moreover, a six-bar linkage can be designed to have more instant inactive joints than a four-bar linkage, hence making the prosthetic knee more stable in the standing phase. In the dynamic analysis, the location of the moment controller was determined for minimum value of the control moment. A testing prosthetic knee mechanism with optimum designed parameters was manufactured for experiments in the laboratory. The experimental results have verified the advantage revealed in the analyses.

[The effects of backpack loading on the gait and corresponding compensatory strategy].

This study was designed to determine the effect of backpack loading on the gait pattern and corresponding compensatory strategy, which is important to the balance control of biped robot and military training. Five healthy subjects were instructed to walk at their preferred speed on level pathway taking three different loads i.e. 6 kg, 12 kg and 25 kg, on their backs. The results showed that the gait pattern was apparently influenced, and the dominant effects were found to be the flexion of hip, knee joints and pitch angle of torso. The stride speed decreased apparently with loading on their backs, but the stride length showed less changes. Besides, the responses to taking loads might be influenced by the strength of body. An apparent multi-joints coordination motor mode was employed to compensate the influences of loading, however, their contributions are different; hip, knee joints and torso pitch made dominant contributions to the compensation while ankle joints made minor. The anterior pitch of upper torso could be employed to adjust the overall center of mass while loading on their backs, the larger the magnitude of loading on their backs, the larger the anterior pitch angle of torso. After the heel touched the ground, the flexion of hip and knee joints were effective for the shock absorption, which means that the stiffness of hip and knee joints can be used to absorb the shock and avoid the trauma of each joints.

[Progress in the study on synergetic control principle of human upper extremity and related issues].

Human upper extremity is the most complex and flexible executor during the human movement, coordination analysis of the synergetic control principle of human upper extremity is of great significance in trajectory planning and real-time control of anthropopathy robots and intelligent prosthesis system. Most studies have only been performed within the last 10 years. This paper surveys the research in the structure characteristic and redundancy coordination principle of human upper extremity, and the developments of various prospects of anthropopathy robots, intelligent prosthesis, gymnastic science and rehabilitation evaluation are discussed.

Synergic analysis of upper limb target-reaching movements.

The topological invariance and synergies of human movements are discussed through the analysis and comparison of upper-limb target-reaching tasks. Five subjects were asked to perform different target-reaching tasks with different indices of difficulty, and the movements were captured using a Vicon 3D motion analysis system. Topological invariance was observed in the trajectories of different task performances. After normalization, the trajectories of the arm tips had very close patterns for different target-reaching tasks. Synergy in the target-reaching movements of the upper limbs was also found among the different joint angles. The joint angles can be fitted using the same format of functions proposed in this study. The parameters in the function can be taken as a characteristic feature of target-reaching movement patterns. A target-reaching movement can be determined by these parameters and the start and end positions.

Motion quality evaluation of upper limb target-reaching movements.

Fitts' Law was extended in the polar coordinate system, and a set of indices for human motion evaluation is proposed. In this paper, the index of difficulty and the index of performance are introduced as the general indices for the quality measure of plane target-to-target movement. As an example, the target-reaching movement of the upper limb, which is a basic functional action of upper limbs in the activities of daily living, was experimentally investigated. Five healthy subjects were asked to perform six target-reaching tasks with different indices of difficulty. All movements were recorded using a Vicon motion analysis system. The movement quality was measured using these evaluation indices.