A spring surface is deformed by the magnitude of the added force, therefore a spring surface is unstable compared to a rigid surface such as solid ground. In order to stabilize a body after landing on a spring surface, it is necessary to move in correspondence with the deformation of the surface. In this study, we examined the role of the lower limb joints in a drop-landing motion on a spring surface.

The following facts were revealed from the study : (1) In the Absorb period, the hip and knee joints are buffered by moving more than the ankle joints according to the change in height of the spring surface. (2) In the Stabilize period, the ankle joints moved according to the change in height of the spring surface ; moreover, the ankle joints moved in response to the vibration of the spring surface.

The roles of the hip and knee joints were different from those of the ankle joints for cushioning and stability. In landing on a spring surface, it was suggested that a specific landing motion strategy was used─unlike that on a solid surface.

The purpose of this study was to investigate the postural control of healthy subjects with a cane on an unstable board. Participants included 10 healthy adults. All participants stood for 30 seconds on the unstable board using a cane in their right arm. A T-handle cane quadripod cane, and Lofstrand crutch were used. Measurements of the center of gravity and the center of foot pressure were undertaken by a 3D motion analysis device (VICON Nexus) and force plates (OR6-6-2000), respectively. Individual activities of the tibialis anterior and soleus muscles and synergistic muscular activity were also calculated. The postural sway of the center of gravity and muscle coactivation of the two muscles were significantly smaller when a quadripod cane was used compared to the other canes. This result supports he superior effects of a quadripod cane for postural control of healthy adults on an unstable surface.

Detailed understanding of the foot deformation during walking is important for ergonomic design of shoe and orthopaedic diagnosis. However, quantitative description of the foot deformation and skin strain during walking have not been fully investigated due to difficulty of measurement. In this study, we aimed to clarify the three-dimensional (3D) human foot deformation and the foot skin strain during bipedal walking by means of digital image correlation (DIC) method. The 3D-DIC method is an optical method to measure 3D deformation of an object by using the stereo-triangulation and the image correlation of speckle pattern on the object surface. Five adult male participants were asked to walk along a walkway at a self selected speed. The dorso-lateral and medial surfaces of the right foot during the stance phase of bipedal walking were filmed using four synchronized high speed cameras. The right foot surface was sprayed with aqueous black ink to draw the speckle pattern. We calculated time change in the 3D foot shape and the skin strain distribution during walking. The accuracy of the shape and deformation measurement was confirmed to be about 0.1 mm, sufficiently accurate for quantitative description of the foot deformation. Our results demonstrated that in the early and late stance phase, the foot surface around the cuboid were stretched in the mediolateral direction. In the late stance phase, the lateral surface of the rear foot was stretched in the dorsopalmar direction vice versa in the medial surface. Proposed methodology may serve as an effective tool to clarify how external surface of the human foot dynamically behaves during walking.

In sports motions, scapular kinematics are important because they are directly involved with humeral motions. However, a method to measure scapular movements in sports motions has not yet been established because of the skin motion artifact. This study aimed to develop a method for noninvasively measuring scapular orientation using a motion capture system. Scapular orientation was estimated with a surface map created from a grid of 100 reflective markers placed on the scapula skin. This measurement was performed for several static humeral positions. Then, the scapular orientation determined by this method was compared with that determined by palpation of scapular landmarks. The results indicated that the developed method accurately estimates scapular orientation. Next, the dynamic scapular orientation in the shooting motion of archery was measured as an example of sports motions. It was concluded that the developed method can accurately estimate the scapular movements during the shooting motion.

Although expert soccer players are skilled at soccer ball juggling on a stable surface, in some players, their performances decrease when juggling on an unstable surface. This means that the subtle difference in skills of expert players can be distinguished using the unstable surface. Expert soccer coach is able to evaluate the level of juggling skills even they observe their juggling on the stable surface. In contrast, if we use the unstable surface, the coaches who have no soccer experience might be able to evaluate the level of juggling skills. In this study we have proven this hypothesis and demonstrated the proper way to evaluate the level of juggling skills even though we don’t have an expert soccer coach. Our results revealed that some players showed greater sway of their kicking feet in the left/rightward direction when juggling on an unstable surface, which makes it easier to distinguish the level of skills. Furthermore, an increase of head sway in a left/right direction may influence the decrease of the juggling performance.

The windlass mechanism is one of the foot functions that generate propulsion at the toe-off in gait. However, the role of the windlass mechanism during running remains unclear. The purpose of this study was to investigate the differences in the windlass mechanism during running and walking. Nine healthy young men participated in this study. The subjects were instructed to run (at 2.5 ms⁻¹) or walk (at 1.3 ms⁻¹) on the treadmill. The medical longitudinal arch angle and hallux dorsi flexion angle (dorsi flexion angle of the first metatarso-phalangeal joint) were calculated in the stance phase as indexes of the windlass mechanism. While the peak value medial longitudinal arch angles during the two tasks showed no significant difference (157.4±6.0° and 156.9±4.9°, respectively), the peak hallux dorsi-flexion angles during running were significantly lower than those during walking (32.9±7.3° and 39.9±9.0°, respectively ; p<0.05). The present study, therefore suggested that the windlass mechanism has a minimal role in propulsion during running.

Kinesthesia is the sense that enables awareness of bodily position, weight, or movement. The perceptual integration of afferent inputs from sensory receptors i.e., muscle spindle or cutaneous, and the efferent inputs from the central nervous system that trigger intentional movement contribute to the generation of kinesthesia. We investigated the mechanism of kinesthesia using the psychophysical index. This paper describes two psychophysical studies : 1) the effect of afferent inputs from muscle spindle on kinesthetic perception during motor imagery, and 2) kinesthetic illusion induced by perceptual integration of proprioception and vision. The results of these studies demonstrate that perceptual integration contributes to kinesthetic perception when the latter is induced by afferent inputs from two antagonistic muscle spindles during motor imagery, or by differing sensory inputs, such as proprioception and vision.

Visuomotor adaptation associated with gain and timing control plays a crucial role in precise control of eye movements. It has been shown that smooth pursuit gain adaptation is induced by repeated trials of a step-ramp tracking with two different velocities (double-step paradigm). In this study, we attempted to determine whether a double-step paradigm with different timing produces pursuit gain adaptation at a specific time. We use a double-step paradigm where target speed changes 400 ms or 800 ms after the target onset during a steady-state pursuit phase. After repeated presentation of this paradigm, pursuit gain showed a significant adaptive change, which was associated with the time when the target speed changed. Furthermore, adaptive capabilities for specific timing were different between humans and monkeys. These results suggest that human pursuit adaptation occurred at a specific time could be due to timing control mechanisms associated with motor preparation.

Kinesthetic illusion is a psychological state in which a person feels as if his or her own body is moving, despite of it being stationary. We investigated cerebral network activation during kinesthetic illusion induced by visual stimuli. In this review paper, we report cerebral network activity that was demonstrated by functional magnetic resonance imaging, during kinesthetic illusion induced by visual stimuli. Except for the primary motor cortex, motor association areas showed higher activity during illusions than during periods of movie observation without illusion. We also report acute clinical effects of illusion on motor function in two patients with stroke. Surface electromyography during movement tasks demonstrated that reciprocal muscular activity gradually appeared after kinesthetic illusion. Further research is needed to fully elucidate the effects of illusions in patients with stroke. Our findings have potential clinical applications.

This study aimed to classify hemiparetic gait according to knee joint motion of the paretic limb during the stance phase. Knee joint angle and shank vertical angle in the sagittal plane were used to classify 35 hemiparetic patients into one of three groups : normal knee pattern (NKP, 15 patients), extension thrust pattern in loading response (ETP-LR, 15 patients), and extension thrust pattern in single stance (ETP-SS, 5 patients). Gait and electromyography were measured and groups were compared. Results showed that the NKP group had sufficient activity in the tibia anterior and sufficient dorsiflexor moment in loading response, and thus had heel rocker function. The ETP-SS group had excessive gastrocnemius muscle activity, which reduced dorsiflexion moment in the loading response. Lastly, the ETP-LR group did not show tibia anterior muscle activity in the loading response and thus had no heel rocker function.

The aim of this study was to investigate the relationship between the alignment of rearfoot and the knee in patients with medial knee osteoarthritis. The patients were classified into pronated or supinated groups based on calcaneus bisector angle. Subsequently, the relationship between the rear foot alignment and femorotibial angle, Kellgren-Lawrence classification, medial joint space as well as pain were investigated. No correlation was found between the rearfoot alignment and the femorotibial angle. Thus it was suggested that the rearfoot would not be affected by it. However, the rearfoot alignment demonstrated correlations with Kellgren-Lawrence classification, medial joint space and pain while walking or climbing stairs. More pronation of the rear foot was found with smaller medial joint space. It was therefore speculated that there would be a mechanism to reduce loading on the medial side of the knee by pronating the rearfoot. If pronation of the rearfoot itself could already reduce pain, an insole with lateral wedge that would further pronate the rearfoot might not be very effective. Moreover, excessive pronation could lead to reverse screw home movement. In conclusion, an insole for patients with medial osteoarthritis should be designed based on the condition of rearfoot.

Knee osteoarthritis (knee OA) is caused by abnormal knee joint mechanics. In order to prevent knee OA progression and achieve this recovery, the mechanical factors affected by knee OA during weight bearing activities, such as gait, need to be clarified. The purpose of this study was to analyze knee joint kinematics and kinetics during gait in patients with knee OA of various severities. A total of 69 knees (62 adults) were divided into three groups (26 normal knees, 16 mild OA knees and 27 severe OA knees). Each subject’s gait was measured by a motion capture system, and the relative femorotibial motion was estimated by a bi-planar roentgenography using the three-dimensional reconstruction technique. Knee kinetics was evaluated based on joint reaction force and joint moment. The point of intersection of the loading axis of the knee (LAK) on the tibial proximal surface was also calculated, and this point was defined as the ‘LAK point’. During stance phase of gait, the knee flexion range, knee anteroposterior shift and anteroposterior range of LAK-point trajectory were significantly decreased in severe OA knees, whereas the medial-lateral direction range of the knee-joint reaction force was significantly increased. The anteroposterior range of LAK-point trajectory was also small in mild OA knees. Moreover, in severe OA knees, the LAK point tended to shift rapidly medially during the loading response. As knee OA progressed, the upper body weight was more locally loaded on the tibial surface, with an increased medial-lateral force in the knee joint. These findings suggest that mechanical transitions may be affected knee OA progression.

A standard baseball pitch is a process that involves a set of complex, whole-body movements that enable kinetic energy to be effectively transmitted from the body-center to the upper limbs, in what we refer to as "the kinetic chain". In this respect, the trunk functions as a relay point. One of the terms used in coaching is “the stretching of the chest”, which is also considered to be related to the kinetic chain. In order to analyze this motion quantitatively, we developed a novel parameter denoted as S, in earlier work. Here, we applied parameter S to the analysis of pitching motion and studied the kinetic chain from the lower trunk to the upper limb, from the perspectives of kinematics and energy transmittance. Experiments using 18 healthy volunteer pitchers revealed that the kinetic chain was clearly evident, between the stretching of the chest and the internal rotation of the shoulder, and was more or less the same, for all subjects.

The purpose of this study was to clarify the quickness of the Taekwondo roundhouse kick in the preparatory phase. Quickness includes objective points (shorter kicking time and higher kicking speed) and a subjective point (impression). We focused on the rhythmic hop in the stepping-motion phase prior to the start of kicking in order to investigate “quickness” including the three points above. The rhythmic hop frequencies of forty-eight Taekwondo practitioners were measured and eighteen male Taekwondo practitioners participated in a further motion-analysis experiment. The experiment trial consisted of roundhouse kicks delivered to a target using the preferred leg. The target height was the same as the subject’s torso. The 3D coordinates of reflective markers on the body segments and the target were captured by a motion capture system. The following results were obtained. i) There was no significant difference between physical characteristics and rhythmic hop frequencies, ii) The subjective point was able to be evaluated by the index of similarity obtained in the rhythmic hop in preparatory phase, iii) A tendency was exhibited that subjects who kicked with a higher kicking speed had a lower subjective point index. In conclusion, it was found that there was the possibility of a trade-off relation between the subjective point and the objective points. Coaches should pay more attention to considering which “quickness” is suitable for each situation or practitioner.

The purpose of the research is to investigate power clean (PC) motion, a quick lift training aimed at improving explosive force generation, to clarify its mechanism from a biomechanical point of view. In the first experiments, the subjects were divided into two groups, 6 in a “skilled” group and 6 in an “unskilled” group, according to their lifting weight limits. The trajectory of lower limb joints during PC was recorded by a motion capture system and joint kinetics data were calculated from the obtained data. The results of the first experiments indicated that all skilled subjects showed greater peak joint torque, and greater torque power than those of the unskilled subjects. They also displayed a counter movement called the short stretching cycle (SSC) typically shown in skilled PC motion. The investigations of joint torque power and joint force power in phase transition during PC suggested some energy flow between adjacent segments must occur to effectively utilize the target areas. The second experiment was performed with different subjects ; 10 skilled and 10 unskilled, in which the joint torque and its rate of torque development (RTD) were calculated from the obtained data. Joint stiffness was evaluated from a newly established joint stiffness index (JSI) calculated from EMG of agonist and antagonist muscle pairs. Experimental results indicated that skilled subjects showed large muscle activity in flexor muscles but extensor activity was almost equivalent to that of the unskilled. Skilled JSI and RTD were larger than those of unskilled subjects at the time of the counter movement phase. These results suggest that the skilled subjects conducted a dexterous control of joint stiffness during SSC to effectively transmit a large amount of energy to exert a large lifting force during PC.

In softball games, fielders need to not only handle the ball, but also concurrently judge the current situation. To do this, they need the visual information of the ball as well as the situation around them. As such, how do fielders obtain the visual information to concurrently handle the ball and judge the situation? The purpose of this study was to measure fielders’line of sight when they catch a ball and judge a runner at the same time. Ten fielders participated in the study. Experiments were conducted under three conditions: (1) catching the ball, (2) judging the situation, and (3) both catching the ball and judging the situation at the same time. Findings indicate that skilled fielders could catch the ball while quickly and accurately judging the situation. Furthermore, they turned their line of sight away from the ball in the early stage of catching and judged the situation, without following the runner with their eyes. In conclusion, the present study suggests that fielders who perform well at simultaneously catching and judging tend to utilize visual search effectively by acquiring the visual information of the ball and the runner at the same time through peripheral vision.

Persons with motor dysfunctions generally use control-interface switches to operate assistive devices. In cases where their condition is progressive, however, they are usually restricted to the use of an on/off switch, due to the need for frequent updates. We have been developing a versatile control-interface switch (VSN/1) that incorporates a photo-reflective sensor array, which is applicable to a wide range of body motions from slight finger movements to voluntary blinking. In its application to blinking detection, however, involuntary periodic blinking leads to much erroneous input. To prevent this, we developed a method of real-time signal discrimination processing, using temporal and amplitude features of signal waveforms originated from blinking. We evaluated overall performance of VSN/1 quantitatively, using 10 healthy volunteers and an amyotrophic lateral sclerosis (ALS) patient. Consequently, functioning-, malfunctioning- and no-response rates in both groups were less than 97.0%, 7.4% and 0.1% on average, respectively, suggesting that VSN/1 has reached a practical level.

People with physical disabilities such as amyotrophic lateral sclerosis (ALS) and cerebral palsy enjoy a significantly improved quality of life through the adoption of assistive devices that are tailored to their individual needs. But these devices employ a control-interface switch that, in its current state of development, can generate erroneous input data, when involuntary body movements like twitch and tremor activate the switch. Then we developed a tri-axial geomagnetic sensor-based switch, GSN/1, which even persons with severe physical disabilities can use. In order to minimize erroneous input, we employed a statistical pattern recognition technique known as Fisher’s linear discriminant. In addition, we developed models of 2 different types of involuntary movements, twitch and tremor, and applied them to the quantitative performance evaluation of GSN/1 used under the condition that involuntary movements also occur. Empirical results revealed conditions of twitch and tremor necessary for maintaining correct inputs on a permissible level.

The construction industry currently faces two major issues. One is the steady retirement of older workers, and the other is the inability to recruit a sufficient number of young workers. One of the reasons behind these problems is the physical demands of construction work. If we could lessen these physical demands, we should be able to resolve these issues to a degree. In this study, we focused our attention on the clothing worn by construction workers. We propose the sewing of elastic materials into workwear, such that it causes tension in the direction in which the worker’s muscles contract. This tension will aid the movement of the construction worker. We obtained electromyogram measurements during actual construction work to determine the degree of physical fatigue and evaluate the degree of assistance provided by the workwear. We used three different types of workwear in three experiments: an X-1 type to investigate the reinforcement layout, an X-2 type in a wall-painting experiment, and a T-type in a floor-painting experiment. Based on the results, we were able to confirm that the assistive function of the workwear assisted the motion of the deltoid muscles in the reinforcement-layout and wall-painting experiments.

A prosthetic foot-ankle unit is one of the key components in a stable and efficient amputee gait. The characteristics of an amputee’s gait depend on the mechanical properties of the units. Thus, several measurement methods have been proposed to evaluate the rollover characteristics of prosthetic foot-ankle units using static or quasi-static loading test devices. To clarify the effects of a dynamic amputee gait on prosthetic foot-ankle units, this study developed a dynamic gait simulated loading device based on concepts found in ISO22675 and ISO/TR22676. The advantage of this approach enables the measurement of the individual dynamic rollover characteristics of various prosthetic foot-ankle units unlike the conventional methods with a prosthesis applied to able-bodied persons or static/quasi-static loading test devices.

 From this viewpoint, in this study, we evaluated the effects of dynamic rollover properties on prosthetic foot-ankle units and stable/unstable shoe combinations under a loading level of 70.0 kg and cyclic loading period of 2.0 s. Based on the dynamic rollover analysis of six kinds of prosthetic foot-ankle units and shoe combinations, we reached the following conclusions. (1) In the middle period of the stance phase, the rollover shape of a SACH foot (1S49) shows a large curvature than that of a SACH foot (1D10). This indicates that a SACH foot (1S49) is suitable for low-activity users to support a stable amputee gait because it has low mechanical deformation. (2) In the stance phase, the rollover shape of a combination with a prosthetic foot-ankle unit and an unstable shoe shows constant curvature in comparison to prosthetic foot-ankle units. This demonstrates that an unstable shoe is one of the key components in amputee gait training because it can improve user activity level without a change in a prosthetic foot-ankle unit. The effectiveness of the dynamic rollover analysis for prosthetic foot-ankle units based on the ISO22675 gait simulated loading device was ascertained through a series of experiments.

Various prosthetic foot-ankle units have been developed and widely used, but for the prosthetist, it becomes difficult to select an appropriate foot-ankle unit and adjust its alignment for each amputee. A. Hansen et.al.developed the quasi-static measuring method of rollover characteristics (locus of c.o.p.: center of pressure) of prosthetic foot in sagittal plane, but loading condition is restricted only vertical force on foot-sole. C. Curtze et.al. measured the rollover characteristics dynamically as the locus of c.o.p. in sagittal plane, but loading condition is constant. Based on the rigid body mechanics, f.c.p. (force contact point) is meaningful compared with c.o.p.. To resolve this problem, we have developed the measuring method of three dimensional locus of f.c.p. on foot-sole under the fixed stance phase loading from heel contact to toe-off generated by the testing device based on ISO/TR22676. Some typical prosthetic feet and orthotic ankle joints were measured and their 3D rollover characteristics were compared.

 Loading device was developed based on the ISO22675 standard. Foot-ankle unit is positioned under the pneumatic servo cylinder which generates the compressive force of double peaks simulating the typical gait cycle loading, and 6-axis load cell is installed just above the foot-ankle unit. The foot plate positioned just under the prosthetic foot rolls from −20 deg (heel contact) to 40 deg (toe off), and generate vertical and shear forces on the foot-sole. Forces and moments measured by the 6-axis load cell are positioned on the center of the load cell, and are equally transformed to a single force vector and a single moment vector on the screw line, based on the rigid body mechanics. The cross point of the screw line calculated from the output of 6-axis load cell and the surface of rolling foot plate is the f.c.p.. The locus of this point plotted on the coordinates system fixed at the center of 6-axis load cell shows the rollover characteristics in sagittal, frontal and transverse planes.

 Three dimensional rollover characteristics of typical prosthetic foot-ankle units and ankle-foot orthoses were measured. Locus of f.c.p. in sagittal plane, frontal plane and transverse plane were calculated and plotted on each graph. The relation between f.c.p. shift from heel to toe and time (sec) was plotted on each foot-ankle unit. The relation between f.c.p. shift from heel to toe and swing foot plate angle (deg) was plotted on each foot-ankle unit. These results showed distinctive feature on each foot-ankle unit, and useful indicators were obtained. Alignment change (plantar flexion-dorsi flexion, inversion-eversion, toe in-toe out) of the foot 1D10 was tried and some distinctive marks were obtained. The method to calculate the three dimensional rollover characteristics as the locus of f.c.p. on foot-sole of prosthetic ankle-foot unit and ankle-foot orthosis under the fixed gait simulated loading condition was settled.

Low-repulsion urethane mattresses can reduce the surface pressure of skin over bony protrusions. It is important to identify the mechanical characteristics of polyurethane foam that contribute to the redistribution of surface pressure over a protrusion and its surroundings. We studied two commercially available urethane mattresses: a low-repulsion urethane foam mattress and a standard polyurethane mattress. Compression and stress relaxation tests were carried out on column specimens on a flat surface, and compression tests were performed on beam specimens on a stepped structure with a high central step and lower tiers on the left and right sides. After relaxation, the stress at a constant compressive strain was used to obtain the stress-strain relationship of the urethane foams. We predicted the redistribution of pressure of a mattress under compression on a stepped surface using a hyperelastic model. The experimental results revealed the presence of a region in the stress-strain curve with large extensibility. Comparison of the theoretical and experimental results revealed that the extensible behavior at low stress levels enhanced the pressure redistribution in the low-repulsion urethane mattress. However, the superiority of the pressure redistribution behavior of the low-repulsion mattress became negligible as the pressure increased.