Vestibulo-ocular reflex is known as one of the involuntary motions of the eyeball.

The action has been mainly investigated from the viewpoint of compensation function for stabilizing the gaze against disturbance on the cranium position.

However, mental workloads may affect on vestibule-ocular reflex.

The related research of the effect of mental workloads on vestibulo-ocular reflex has not yet appeared.

First, we conducted the identification of vestibulo-ocular reflex for a particular person based on the mathematical model proposed by Haslwanter et. al.

It is confirmed with experiments that the identified model for each person predicts the actual ocular movements well.

Second, we tested the capability of the identified model with manual tracking tasks.

During the tracking task, aural subtasks, which are mental arithmetic of two digits addition, were continuously given to evaluate the error from the identified model which predicts the subject response without the subtask.

The results show that mental workloads affect vestibulo-ocular reflex and can be evaluated by the identified model.

A model of muscular fatigue, which is used as part of a Hill type mechanical model, has been developed to evaluate the effects of muscular fatigue on the characteristics of force generation in motion analyses. For this purpose, we considered the states of activity of each motor unit type and the order of recruitment of motor units. The states of motor units in the model were divided into four conditions depending on their activity and fatigue. The changes of the states of each motor unit were formulated by the sets of differential equations based on the relationship among muscular fatigue and recovery, and activity of muscle. Furthermore, motor units were also categorized into three types depending on their characteristics of force generation and fatigue. The order of recruitment of motor unit types was modeled based on the size principle. The model correlates well with the response of the model of Liu et al. at the maximum voluntary contraction condition and the results of Ikai's fatigue test at the dynamic condition. The degrees of muscular fatigue were evaluated by the present model with different proportions of motor unit types. Thus the present muscular fatigue model is able to describe the basic response of muscular fatigue and to simulate the differences of characteristics of muscle.

Understanding the functional anatomy of the chimpanzee hand as a model for the hands of ancestral hominids is essential for understanding the evolution of morphological bases for human precision grip capabilities. Therefore, we constructed an anatomically based mathematical model of the chimpanzee hand musculo-skeletal system. The skeletal part was determined based on serial CT scans of a hand skeleton. Joint surface areas were approximated by a quadratic function to define rotation axes and radii of rotation. The path of a muscle was defined by a series of points connected by line segments. We dissected a chimpanzee cadaver to obtain quantitative data on the chimpanzee hand musculature. As an example of biomechanical analyses using the proposed model, we simulated pincer grip and estimated the direction and magnitude of maximum biomechanically possible grip force vector. Comparisons of the simulated results with those calculated for the human hand pincer grip suggested that human distinctive morphological features, especially that of the first dorsal interosseous muscle, may facilitate precise pinch grip, demonstrating efficacy of the proposed model for evaluating effects of the musculo-skeletal features in the precision grip capabilities.

The purpose of this study is to clarify the mechanism of competitive swimmers' lumbar injury from the viewpoint of biomechanics, focusing on the lumbar load and behavior. First, whole body simulation for the six beat crawl is carried out by using the swimming human simulation model SWUM, which has been developed by the authors, and the joint force and torque at lumbar are calculated. Next, by the use of the two-dimensional musculo-skeletal model for lumbar on the sagittal plane, the movement of the lumbar spine and the muscle force are calculated. By the simulation, it was found that the intervertebral joints of L5/S1 and L4/L5 move with larger amplitudes than the other joints, and that these can be reduced by an increase in stiffness of the inner muscles. In order to verify the simulation results, an experiment using X-ray cineradiography and a developed setup was conducted for four subjects. In the experiment, behavior of each lumber vertebrae and load are measured. It was found that the amplitudes of L5/S1 and L4/L5 joints become larger than the others also in the experiment, and that these amplitudes are reduced in the case of trials with the tense Psoas Major.

The purpose of this study is to construct a mathematical model which can reproduce the variation of blood pressure and cardiovascular dynamics during physical exercise, and also to clarify that mechanism by a computer simulation. Pedaling exercise was assumed as an objective human movement, and a musculoskeletal model reproducing pedaling motion with given rotation speed was constructed. A mathematical model integrating the musculoskeletal and cardiovascular systems was established by referring to previous cardiovascular models with a continuous time system and by adding cooperation mechanisms between both systems such as characteristics of the central command and the peripheral chemoreceptor. Additionally, a simple model which can calculate the flow of arterial blood from blood pressure was embedded in the integration model so as to consider oxygen supply corresponding with blood pressure variation. Simulation results such as blood pressure variability and cardiac cycle wave closely agreed with characters of the experimental results. The simulation result also pointed out importance of the shift in the baroreceptor set point.

Analysis of the three-dimensional (3-D) kinematics in vivo is expected to be one of the most important techniques for post-operative evaluations of total knee arthroplasty (TKA) design. The aim of this study was to analyze motion of an implanted knee in daily life by using image matching technique with a high-resolutional flat panel detector (FPD). We analyzed knee prostheses during kneeling activity. Five cruciate-retaining (CR) and five posterior-substituting (PS) designs were examined using this newly developed motion analysis method. Our study demonstrated that it was possible to reproduce the relation of contact position between a femoral component and a polyethylene insert. As a result, our technique showed that the edge contact of a polyethylene insert and post-cam contact were respectively occurred in CR and PS knees. Additionally, motion analysis of artificial knee implants could clarify a typical motion pattern depending on patients.

Seventy-seven percent of care givers and sixty-four percent of nurses are reported to experience back pain. No clinical device simply yet effectively reduces loads placed on the lower back. In this research, we report on a prototype device developed for practical use that reduces the load on the lower back. The device was designed in a simple structure for use in a deep forward leaning posture at bedsides. This paper discusses the theoretical analysis based on a mechanical model, motion analysis by measuring joint angle variations in typical nursing movements (e.g. transfer to and from the wheelchair and bedside), and the evaluation of the exertion encountered in nursing from EMG signals of the erector spinae when loads are applied. In addition, the device was tested to evaluate its potential restrictions to daily activities, i.e. sitting on a chair and crouching to pick up items on the floor. The results showed that the device does not constrain body movement and that the required exertion of subjects to support a large load is substantially reduced by use of the device, especially in the deep forward leaning posture as targeted.

The main object of this study is to establish the measurement and analysis of three dimensional human movements for designing wheelchairs. First, we have developed an instrument system, which can be attached to several types of wheelchair, to measure the three dimensional displacement/orientation of upper limb and force/moment at the contact point between the hand rim and the user's hand. The measurement values of each user are used to calculate the dynamic properties of the user function. Second, we have defined a new dynamical manipulability using an ellipsoid so as to find out the best direction of driving force at each instance in the driving cycle. Kinematic relationship between the generated tensions of muscles and the effective force for wheelchair propulsion can be seen with the ellipsoids along the trajectory of the user's hand. Finally, a new method has been proposed to find the optimal position of the seat or the optimal driving form based on the movement of the upper limb of the user, experimental data of generated force and moment, and a rigid link model for the upper limb and body. We have given an example to prove that the designed wheelchair effectively reduces the user's mechanical work by as much as 20%. The results of this study can serve as a platform to design the optimal wheelchair for each individual user.

There is a psychological dilemma associated with a loss of physical independence. Many people do not want to be stigmatized by having to use canes, wheelchairs, or other equipment that makes them appear disabled. Among the most challenging problems is that of decreased lower limb mobility, which restricts the distance a person can walk without assistance. Here we describe a hybrid mobility assistance device to address this issue. The device is four-wheeled, permitting the user to walk naturally while a servo motor amplifies normal walking speed. Its main components are a treadmill and two front driving wheels. Sensors in the treadmill detect anterior-posterior forces that are applied to the surface during walking. Rotational speed of the driving wheel motors is controlled by signals from these sensors. Computer software monitors the walking pattern as measured by the treadmill motor. Preliminary evaluations suggest that this device is both safe and effective for use by middle aged and older adults.

In this study an attempt was made to apply a simulator of the human ambulatory stride wearing a hip disarticulation prosthesis (HDP) as a design support system. The simulator was based on a neuro-musculo-skeletal model that was developed in our previous study. First, two design proposals of the HDP were submitted. Each mechanical model of the proposals was constructed and introduced to the simulator. It was confirmed that the human models wearing the proposed HDPs were able to walk on the simulation after the normal turnings of mechanical properties and a high number of iteration computations were conducted to optimize the process of the neural parameters. Next, using results of the simulation as a reference, a prototype of a hip joint of an HDP was designed and manufactured, which will be able to assist flexion-extension motion around the hip joint. An analysis of walking motion using the prototype was performed. Then the maximum knee flexion angle of the HDP was measured at twice the height as that of walking using the normal HDP. This contributed to making the gait more natural in appearance. In addition, the walk patterns using the prototype HDP agree with the results of the simulator, thus validating the simulator. Finally, the effectiveness of the support system design was examined and further problems to be solved were identified.

The study of locomotive functions and mechanisms of the minute organisms is of fundamental interest and importance with respect to the development of various microrobots. Therefore, extensive investigations for a realization of various microrobots have been conducted. This paper describes the nymph swimming analysis using the high speed video camera system. The gait analysis of some insects is also described in order to clarify the difference between swimming and walking. Based on such swimming analysis, the micro swimming mechanism with the wireless energy supply system was produced experimentally. Frequency characteristics of the swimming mechanism propelled by the alternating magnetic field and a NdFeB permanent magnet were investigated for the leg fins of various lengths. It was found that the swimming velocity of the micromechanism indicated the highest value in the region of 20 Hz. This paper also describes the process of the development of the micro swimming mechanism.

In order to clarify the jaw movement mechanism, we have been developing an autonomous jaw-movement simulator, JSN, with a life-like anatomical structure and a physiological control scheme. In this study, the simulator was updated by improving a 2-D bite-force sensor into a 3-D one, by installing a temporomandibular joint-loading sensor, and by slightly modifying actuator driving signals for a chewing-like jaw movement. In an attempt to carry out a performance evaluation for the present simulator, JSN/2C, as a chewing-movement simulator capable of biting food, we scrutinized 1) measurement accuracy of the bite-force sensor;2) 3-D trajectory of the lower incisor, 3) time series of 3-D bite force applied to the upper first molar; and 4) the relationship between activities of jaw-closing muscles and bite-force/Temporomandibular joint loading during a bite. Consequently, the simulator JSN/2C was verified to satisfy several necessary conditions required for a chewing-movement simulator.

The concept of affordance is introduced to generate robot behaviors for performing tasks. In disassembly of a mechanical product, the disassembly process is considered to proceed as the product offers the affordances for behaviors of removing its parts and the agent, may it be a human or a robot, accepts them. Considering analogically that the agents are of a biological species, if they are placed in the environment rich with disassembly objects and the success of disassembly leads to the preservation of the species, the agents will acquire more efficient behaviors. An agent may find plural affordances in the environment simultaneously and the problem arises about which affordance to accept. We introduce regulations in accepting affordances, which correspond to the known psychological phenomena of adaptation and early selection. We claim that these regulations are a new kind of affordances and that the fundamental and regulative affordances together constitute an architecture for the integral behavior of the agent. The simulation using the Genetic Algorithm demonstrates that the disassembly robots evolve themselves for higher efficiency by developing regulations in accepting affordances in the environment with specific products.

Master-slave systems require human operation. As such, human perception is a key element that should be taken into account in the design of any master-slave system which desires high maneuverability. However, human perception has often been overlooked in the early stages of machine design. In fact, system maneuverability has typically been assessed using sensory evaluation techniques after prototypes have already been made. The purpose of this study is to extract features of perception abilities from measured data and to derive objective conditions for master-slave system designs. In particular, this paper will deal with the difference limen of force perception. In this study, difference limens are measured by using a master device to simulatea continuously changing force. The position, velocity, and force of arm movements generated by subjects are measured. We investigate how the time derivative of simulated force influences the difference limen. It has been found that subjects can detect a small change when the simulated force changes rapidly. However, they are unable to detect the change when the simulated force changes slowly. In effect, subjects change their power according to the simulated force even if they are unconscious of force change. Based on these characteristics of human abilities obtained from measurements, we discuss the conditions of a scaling method for master-slave systems.

A dummy skeleton with 16 joints and 38 degrees of freedom in all which imitated the rigid-body dynamics and joint resistance characteristics of the human body was developed. The joint resistance characteristics of this dummy were decided from measurements of the relationship of the joint torques and joint angles in one male subject who had nearly average joint characteristics in a previous examination of several extremity joints. The joint resistance has non-linear characteristics which greatly increase near the range of motion limits. A compact joint mechanism using the bending and compression resistance of a C-shaped resin was developed to reproduce this characteristic. The weight and center of gravity of the dummy segment came within 10% of the goal value. The joint resistance values were approximately the same as those of humans, and were in the range of dispersion of the joint resistance measurements. From the imitated joint resistance, the developed dummy becomes stable with the natural limb position which corresponds to various support conditions. The dummy can be applied to caregiver training and rescue training.

Microgravity induces osteoporosis. Osteocytes are considered to act as a mechanosensor in bone tissue. They are the most abundant cells in bone and are distributed throughout the bone matrix. However, very little is known about the detailed mechanism of osteoporosis occurred under microgravity. Therefore, the aim of this study was to examine the effects of multi-dimensional gravity on osteocytes and bone marrow cell differentiation. We developed a newly experimental apparatus, by which osteocyte-like cell line MLO-Y 4 cells can be cultured under multi-dimensional gravity on the ground. When osteocytes were cultured on coverslips for 2, 4 and 6 days, cell proliferation was significantly inhibited in the cells exposed to multi-dimensional gravity compared with control cells. Moreover, MLO-Y 4 cells forming cell-to-cell networks were cultured for 24 hours in multi-dimensional gravity. Double fluorescence staining technique revealed that cell-to-cell communications via the gap junction were significantly decreased in multi-dimensional gravity. Bone marrow cells were cultured for a week using a conditioned medium (CM) obtained from osteocyte culture under multi-dimensional gravity. There were no significant differences in relative ALP (alkaline phosphatase) activity, on the other hand, TRAP (tartrate-resistant acid phosphatase) activity was significantly increased by adding CM from osteocyte culture exposed to multi-dimensional gravity. Those results suggest that the initial stage of bone resorption under multi-dimensional gravity would be regulated by osteocyte, possibly by soluble factors secreted by osteocytes.

The purpose of this study was to estimate the structure of active motor units through an inverse analysis of surface EMG. Firstly, the surface EMG (motor unit action potentials; MUAPs) were recorded from the biceps brachii by an electrode array which was perpendicularly arranged in the muscle fiber direction. The depth and intensity of active motor units were estimated through the inverse analysis. The inverse analysis was executed by searching the parameters minimizing the difference between recorded surface potential and calculated surface potential. Secondly, the relationships between the structure of motor units and estimated value were clarified through the inverse analysis of the surface potential generated by the models of motor units which have various radius and fiber density as parameters. The radii of all or partial area and fiber densities of motor units were estimated by applying the relationships derived in this numerical simulation.

It is known that the MMG (mechanomyogram) reflects the mechanical function of the muscle, but its generating mechanism has not been sufficiently clarified. In this study, when the gastrocnemius of the rat was electrically stimulated, the acceleration-MMG and the displacement on the surface of the muscle were measured using an accelerometer and a laser displacement transducer, respectively, and the intramuscular pressure was simultaneously measured using an optical fiber inserted into the muscle. The generating mechanism of the acceleration-MMG was suggested by the comparative reviews of the following data obtained from the muscle where the induced twitching occurred: the latencies, propagation velocities and amplitudes among the acceleration-MMG, displacement and pressure. Dantrolene, which suppresses the emission of Ca^2＋ from the sarcoplasmic reticulum, was also injected intramuscularly and the measurements were similarly carried out. The following conclusions were obtained: (1) the MMG measured by the accelerometer can be dynamically transformed into the displacement of the surface; (2) the MMG consists of the propagation and composition of the shear wave caused by the change of intramuscular pressure with the muscle contraction;(3) the location of neuromuscular junction can be estimated from the latency of the MMG and the intramuscular pressure wave.

The purpose of this study was to investigate muscle hardness related to isometric contractile level and muscle fatigue by the indentation method. The first experiment involved fifteen healthy volunteers. Their upper arms were indented at elbow angles of 0, 45 and 90 degree varying isometric contractile force from 0 to 100% MVC, every 10%. The indentation depth, reaction force and isometric contractile force were recorded. The relationship between the indentation depth and the reaction force was approximated well with the proposed model and the elastic indices were estimated. The elastic indices were more proportional to the isometric contractile level than other indices using linear approximation of the force-indentation curve. The relationship between the elastic indices and isometric contractile levels did not depend on the elbow angle.

In the second experiment, the elastic indices and relative blood flow change after repetitive eccentric-concentric exercises (40% and 20% MVC) were investigated. Both the elastic indices and the relative blood flow change were high just after the exercises and then decreased. However the elastic indices decreased more rapidly than the relative blood flow change. The results of this study suggested that the blood flow change affected the muscle hardness but there would be other mechanisms to determine the muscle hardness.

The shoulder joint has a wide range of motion. On the other hand, this joint, has unstable and weak anatomical structure. Therefore, the soft tissue that surrounds the shoulder is damaged easily by overuse during sports activities. These injuries create more laxities of the shoulder. These laxities cause other serious problems of the patient's shoulder. Clinically, it is very important to evaluate the contact patterns of the glenohumeral joint quantitatively to diagnose the joint disorders. Few studies reported on the contact patterns of the glenohumeral joint. These reports used cadaver models to investigate the contact patterns. However, the normal subject's contact patterns are needed to evaluate the shoulder joint movements for abnormal subject. We estimated the distance distributions between the humeral head and the glenoid fossa by employing an open MR system in order to investigate the articular contact patterns of the glenohumeral joint. To validate our method, we estimated the closest point of the normal glenohumeral joint. The results showed that the normal shoulder, the humeral head and the glenoid fossa, have reasonable congruities during the humeral elevation.

A muscle active simulator for cadaveric lumbar experiments was developed. This simulator can generate wire tensions as the complex and continuous muscle forces of 7 muscles in lumbar spine;m. rectus abdominis, m. obliquus internus abdominis, m. obliquus externus abdominis and m. erector spinae. The wire tensions were controlled by servo actuators consisting of stepper motors and loadcells. The muscle tensions were obtained by a musculoskeletal lumboligamentous model and actual motion data. The maximum tension was limited to 100 N to avoid damaging cadavers. Under the muscle tensions of the flexion 30 [deg], the extension 20 [deg], the lateral bending 20 [deg] and the axial rotation 10 [deg], the motions of two fresh cadaveric lumbar spines were almost similar to theactual motion. The lumbar spine bent laterally even in the flexion motion because of the asymmetry spinal shape. When the lumbar spines bent laterally, L5 vertebra bent reversely. In the axial rotation, L1 rotated the most. L2-L3 moved as one unit, but L5 fixed on the sacrum and L3 bent laterally because of the wedge shape of intervertebral discs.