This study aimed to determine mechanisms involved in the decrease of knee adduction moment (KAM) when waking with a contralateral cane without any constraint. Ten young subjects performed walking under two conditions: unassisted (no cane) or with a cane. After collecting data from the stance phase of the left foot, kinematic and kinetic data at early and late peaks of KAM were extracted for further analyses. When using a cane, early and late peaks of KAM decreased (p < 0.05) by 20.5% and 29.6%, respectively. Stepwise multiple regression analysis showed that the moment arm accounted for 59% and 95% of the variance of early and late KAM peaks, respectively. This reduction in moment arm occurred primarily due to lateral rotation of the GRF. Regarding the mechanism behind this, it could be due to the following: 1) by using a cane, the synthetic center of pressure shifted medially, which caused synthetic GRF to become more vertical than that of an unassisted walking and accordingly, and 2) the decrease of horizontal component of synthetic GRF reduced horizontal component of foot GRF, leading to lateral rotation of foot GRF. Understanding these mechanisms might help us improve effective use of canes.

In the rehabilitation of upper limb function impaired by stroke, facilitating the coordinated activation of multiple muscles is desirable. This study aims to analyze the coordination patterns of the tonic and phasic components of EMG during a reaching task and to investigate how the phasic component changes in relation to reaching speed. The analysis focused on the shoulder and elbow joints. EMG was recorded at five different speeds, with the slowest speed selected to represent the tonic component. The tonic component was then removed from the total EMG at the other four speeds to extract the phasic component. Correlation coefficients were calculated between the tonic component and joint angles, as well as between the phasic component and joint angular accelerations. For the tonic component, as joint angle increased during reaching, muscle activation also increased to counteract gravitational moments and enhance joint stiffness. For the phasic component, as reaching speed increased, the correlation between acceleration-deceleration patterns and muscle activation also increased. This suggests a greater synergistic contraction for enhanced acceleration and deceleration, as well as increased antagonistic contraction to ensure dynamic stability during faster movements

Climbing stairs places a greater load on lower limb joints compared to walking on level ground. Variations in anatomical structures and muscle characteristics between genders suggest potential differences in the distribution of required mechanical work among the three lower limb joints. This study aimed to identify gender disparities in the allocation of mechanical work to lower limb joints during stair climbing. A total of thirty-six adults (equally divided between men and women) participated in the study. Participants ascended stairs equipped with force plates at their comfortable speeds, while motion was captured using nine cameras. Inverse dynamics analysis was employed to calculate the mechanical work performed by each joint during four phases of stance: weight acceptance, pull-up, forward continuation, and push-up. Male participants exhibited significantly higher mechanical work than females at the hip and ankle joints (p < 0.05) from the 1st- 3rd phases and the 2nd phase, respectively. Conversely, female subjects displayed greater knee joint work during the 2nd- 3rd phases (p < 0.05). Notably, a pronounced gender difference was observed during the 2nd pull-up phase, where body mass is lifted by a single leg. These findings suggest that men and women employ distinct strategies in distributing mechanical work across lower limb joints.

The purpose of this study was to analyze dynamic postural balance against tilting perturbation in the young and the elderly. Twenty-eight young subjects and 22 elderly subjects participated in this study. Subjects performed dynamic balance test on a force plate during tilting perturbations (tilt-up and tilt-down). As outcome measures, peak distance and velocity were calculated from center of pressure (COP). Two-way ANOVA were performed for the outcome measures with the independent factors of age and gender. COP peak distance of the elderly was significantly greater than that of the young (p < 0.05). Velocity of COP showed age difference (p < 0.001) and also interaction effects only in tilt-up perturbation (p < 0.05). Especially, age-related difference existed in only women (p < 0.001). The age-related changing of women in the dynamic balance may be related to the greater fall rate of elderly women.

This study aims to quantify the effects of medication (Med) and deep brain stimulation (DBS) on resting rigidity in patients with Parkinson"s disease. We tested 10 limbs of five patients under each of four treatment conditions: 1) baseline, 2) DBS, 3) Med, 4) DBS + Med. Rigidity at the wrist joint was assessed using the Unified Parkinson"s Disease Rating Scale (UPDRS). The examiner randomly imposed flexion and extension movement on patient"s wrist joint. Resistance to passive movement was quantified by viscoelastic properties. Not only rigidity score but also damping constant showed improvements in rigidity by DBS and Med treatments (p<0.05). This indicates that the viscosity can represent the change in rigidity due to DBS as well as Med, which was manifested by UPDRS score.

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has been found to be effective treatment of Parkinson’s disease (PD). This study aims to evaluate the effect of DBS for rigidity during DBS surgery. Six Parkinsonian patients who received STN-DBS surgery participated in this study. The examiner imposed flexion and extension of a patient’s wrist randomly. Resistance to passive movement was quantified by viscoelastic properties (two damping constants for each of flexion and extension phase and one spring constant throughout both phases). All Viscoelastic constants decreased by DBS (p<0.01). Specifically, reduction in damping constant during flexion (Bf) was greater than those of damping constant during extension (Be) and of spring constant (p<0.05). Bf would be appropriate for evaluation of effect of DBS for rigidity during DBS surgery.

The aim of this study was to identify both the mechanical and reflex properties associated with spasticity in hemiplegic patients. Ten hemiplegic patients were included in this study. Multiple pendulum tests were executed for each subject, and knee joint angle and EMG of Rectus Femoris muscle were measured. The neuromusculoskeletal system model was developed from generally accepted mechanism and identified through minimization of the error in the modelpredicted pendulum trajectories. The identification was successful in terms of small error in simulated kinematics and high sensitivity and precision of simulated torque against EMG activity. The reflex threshold showed significant difference between different clinical scores (p＜0.01) and significant negative correlation (r=-0.93) with the EMG duration. It is expected that the suggested method may help in understanding mechanisms underlying spasticity.

The objective of this work is to develop the knee joint model for representing various pendulum motions and quantifying the spasticity. Knee joint model included the extension and flexion muscles. The joint moment consists of both the active moment from the stretch reflex and the passive moment from the viscoelastic joint properties. The stretch reflex was modeled as nonlinear feedback of muscle length and the muscle lengthening velocity, which is physiologically-feasible. Moreover, we modeled the spastic reflex as having dynamic threshold to account for the various pendulum trajectories of spastic patients. We determined the model parameters of three patients who showed different pendulum trajectories through minimization of error between experimental and simulated trajectories. The simulated joint trajectories closely matched with the experimental ones, which show the proposed model can predict pendulum motions of patients with different spastic severities. The predicted muscle force from spastic reflex appeared more frequently in the severe spastic patient, which indicates the dynamic threshold relaxes slowly in this patient as is manifested by the variation coefficient of dynamic threshold. The proposed method provides prediction of muscle force and intuitive and objective evaluation of spasticity and it is expected to be useful in quantitative assessment of spasticity.

We analyzed the pressure, impulse on 24 sensors location under the foot using the Parotec system. Total 7 kinds of shoes, i.e. sport shoe, high heel shoes (5㎝ heel, 8㎝ heel, 13㎝ heel), platform shoe, inline skate, and heelys were evaluated for 20 normal subjects. Compared with those of sport shoe, greater pressure and impulse were shown on the 1st phalange and the 1st metatarsal head and greater impulse on the medial tarsal bone in high-heel shoes. Greater pressure and impulse were shown on medial metatarsal bone and the lateral tarsal bone in platform shoe. Greater impulse was shown on the medial tarsal bone in inline-skate. Heelys shoe showed smaller impulse on the central area of foot. The result of this study is expected to provide useful information about the relationship between the shoe type and the foot pathologies.

The purpose of this work is to develop the FES controller that can cope with the muscle fatigue which is one of the most important problems of current FES (Functional Electrical Stimulation). The feasibility of the proposed FES controller was evaluated by simulation. We used a fitness function to describe the effect of muscle fatigue and recovery process. The FES control system was developed based on the biological neuronal system. Specifically, we used PD (Proportional and Derivative) and GC (Gravity Compensation) control, which was described by the neuronal feedback structure. It was possible to control of multiple joints and muscles by using the phase-based PD and GC control method and the static optimization. As a result, the proposed FES control system could maintain the cycling motion in spite of the muscle fatigue. It is expected that the proposed FES controller will play an important role in the rehabilitation of SCI patient.

The purpose of this paper is to develop a more precise damper model of the joint for the quantification of the joint mechanical properties. We modified the linear damper model of a knee joint model to nonlinear one. The normalized RMS errors between the simulated and measured joint angle trajectories during passive pendulum test became smaller with the nonlinear damper model than those of the linear one which indicates the nonlinear damper model is better in precision and accuracy. The error between the experimental and simulated knee joint moment also reduced with the nonlinear damper model. The reduction in both the trajectory error and the moment error was significant at the latter part of the pendulum test where the joint angular velocity was small. The nonlinearity of the damper was significantly greater at thin subject group and this indicates the nonlinearity is a useful index of joint mechanical properties.

The purpose of this paper is to suggest a practical and simple method for the identification of the joint mechanical properties and to apply it to human knee joints. The passive moment at a joint was modeled by three mechanical parts, that is, a gravity term, a linear damper term and a nonlinear spring term. Passive pendulum tests were performed in 5 fat and 5 thin men. The data of pendulum test were used to identify the mechanical properties of joints through sequential quadratic programming (SQP) with random initial values. The identification was successful where the normalized root-mean-squared (RMS) errors between the simulated and experimental joint angle trajectories were less than 10%. The parameter values of mechanical properties obtained in this study agreed with literature. The inertia, gravity and the damping constant were greater at fat men, which indicates more resistance to body movement and more energy consumption for fat men. The suggested method is noninvasive and requires simple setup and short measurement time. It is expected to be useful in the evaluation of joint pathologies.

The purpose of this study is to generate cycling motion for FES (functional electrical stimulation) using knee muscles only. We investigated the possibility by simulation. The musculoskeletal model used in this simulation was simplified as 5-rigid links and 2 muscles (knee extensor and flexor). For the improvement of the present feedforward control in FES, we included feedback path in the control system. The control system was developed based on the biological neuronal system and was represented by three sub-systems. The first is a higher neuronal system that generates the motion command for each joint. The second is the lower neuronal system that divides the motion command to each muscle. And the third is a sensory feedback system corresponding to the somatic sensory system. Control system parameters were adjusted by a genetic algorithm (GA) based on the natural selection theory. GA searched the better parameters in terms of the cost function where the energy consumption, muscle force smoothness, and the cycling speed of each parameter set (individual) are evaluated. As a result, cycling was implemented using knee muscles only. The proposed control system based on the nervous system model worked well even with disturbances.