Optimizing pedaling torque waveform is one of effective approaches to high pedaling efficiency. Usually, the pedaling torque waveform is optimized inefficiently by trial and error based on the pedaling torque measured by a power meter. An appropriate theoretical model for estimation of the pedaling torque is expected to drastically improve the inefficient optimization process. In this study, we derived a theoretical equation for the pedaling torque based on the link-segment model of the lower body and the crank. The pedaling torque can be estimated by the derived equation with the trajectories of motion of the legs and the crank during pedaling measured by accelerometers. The estimated pedaling torque was compared with that obtained by the power meter. As a result, both the pedaling torques were consistent to some extent with each other. However, a large error remained at the peak value even if the external force associated with the pedaling force was considered. Thus, it is necessary to improve the estimation accuracy by optimizing the measurement method of the trajectories of motion with the accelerometers.

Recently, the IMU motion capture system has been developed as a system that can be used in sports practice. In this study, we examined the accuracy of the kinematic variables measured/calculated with a commercially available IMU motion capture system for three whole body movements (squat, walking, and jump) by using an optical motion capture system for determining the corresponding kinematic variables as reference. The result demonstrated high correlations (> 0.94) between the two systems for the positions of the center of mass on the main motion axis. In the walking task, the IMU system overestimated the total distance traveled but the amount of the overestimation was limited to about 3%. In the center of mass velocity data of IMU system, a large ‘spike’ of measurement error was observed at the instant of landing and/or the instant of take-off. This might be due to the algorithm of the IMU system used for detecting whether the foot was placed on the ground. The rate of change in the vertical velocity of the center of mass was found to match well the theoretical value (gravitational acceleration) during free fall. The vertical angle of the long axis vector of each segment showed an average difference of 11.5 degrees compared to the value calculated from the optical system. The results indicate that the selected kinematic variables can be measured by the IMU motion capture system with an acceptable accuracy, so that it can be applied as a new measuring device in measurement in an environment where it was difficult to measure with an optical system, especially in sports motion analysis including the aerial period.

In this paper, we propose the estimation method of face geometry during a curve using a belt-shaped inertial sensor system in which multiple inertial sensors are mounted in a belt shape. In order to reduce the effects of dynamic acceleration and drift error during operation, the roll angle and pitch angle, which are the attitude information of the inertial sensor, are estimated using sensor fusion that focuses on velocity information including centrifugal acceleration during a curve motion. The shape of the entire belt-shaped inertial sensor system can be estimated by conducting forward kinematics analysis using the rotation matrix calculated from the attitude information and the distance between the sensors and applying the adaptive Kalman filter. The effectiveness of this method is evaluated by comparing the estimation result with the measurement result of the motion capture system. It is shown that high-precision shape estimation is possible by using this method even in an environment where dynamic acceleration acts significantly during curved motion.

In this study, we conducted the 3-axis acceleration analysis of figure skating jump using inertial sensors. In the motion measurement of figure skating jump, the measurement area is wide, and the figure skater conducts high speed rotational motion. Therefore, we used the inertial sensor system as simply motion measurement device. We conducted the measurement experiment of the figure skating jump by a high-level figure skater, we obtained the 3-axis measurement information of inertial sensors in the triple flip jumps and the quadruple salchow jumps. The results of combining angular velocity and acceleration indicated the high repeatability. Furthermore, we conducted the 3-axis acceleration analysis in quadruple salchow jumps using the sensor outputs and the self-assessment. The result of high point in self-assessment indicated the high acceleration, and the effect by composite axis component in centrifugal acceleration was indicated. These results indicated the importance of body inclination during the jump motion.

In gymnastics parallel bars, friction between hands and parallel bars is very important for the gymnasts. The authors inspired by the grips for the horizontal bar and the rings and develop a new grip for the parallel bars which can support athletes improve their friction between hands and parallel bars. The forces acting on a parallel bars was estimated from the filming of actual performances. The results showed that the force acting on the parallel bars was about four times that of the body weight. It was also suggested that the hand slips vertically where the maximum joint force is reached and where the frictional force is zero. A grip was developed based on the experimental results.

The performances on a pommel horse were analyzed for the data acquired with a motion capture system to develop a performance evaluation method. In previous papers, we presented the Lissajous diagram for a double-leg circle on a pommel horse, taking the circling motion of tiptoe on a nearly horizontal plane and the rolling motion of a body around a longitudinal axis. The Lissajous analysis showed how the circling and rolling motions were in phase with each other and evaluated how good the performance is by comparing the performance with a simple mathematical model. In the present investigation, we aimed at the extension of the Lissajous analysis to other different techniques of the pommel horse performance, including travelling and body-turning double leg-circles, and a scissors performance. Simple mathematical models for these techniques have been derived as reference motions. It is shown that the Lissajous analysis can be extended to evaluate most of the techniques on a pommel horse by comparing with the model reference motions.

This work clarifies a possible approach toward the motion generation and control of the standing backward tuck somersault, one of the fundamental maneuvers in gymnastics. We show how to generate various types of backward tuck somersaults by focusing on the angular momentum distribution within the body segments. For this purpose, we use the Relative Angular Acceleration (RAA) controller that was developed for humanoid robot control. The desired trajectories for the center of mass and the system angular momentum are derived from the human performances of the somersault task. Furthermore, the generated motions are analyzed to enhance the performance of the maneuver via computer simulation. Our analysis revealed that the duration of the tuck phase in mid-air and the landing position of the foot play an important role for a stable performance of the task. We achieved similar results as in the field of sports biomechanics.

We developed a new suit for Tokyo 2020Olympic and Paralympic cycling road races. Several clothes were tested by using a truncated cone wrapped with cloth in the wind tunnel. On the basis of the drag measurements, several pilot suits were made. They were tested by using a full-scale mannequin which can pedal the bike in the wind tunnel. Finally, we succeeded in developing the new suit for Tokyo 2020Olympic and Paralympic cycling road races, which is superior to Beijing model.

In recent years, research and development of competitive wheelchairs has been actively carried out in preparation for the Paralympics in our countries. The purpose of this study is to reveal the driving performance of a wheelchair for tennis depending on the height of the rear wheel caster and to improve the performance of the athlete. A tennis wheelchair generally consists of two driving wheels, two front wheel casters and one rear wheel caster, and the weight of the wheelchair is distributed on each tire and transmitted to the ground. When the height of the rear wheel caster is changed, the pressure distribution on the ground when the athlete rides on the wheel changes. The stability and propulsive force during driving were revealed by using 9-axis acceleration sensors, surface electromyography and running time data. As a result, when the rear wheel caster was in the "High" position, which relies heavily on the drive wheel weight, one drive had more thrust when going straight, and the number of drives was reduce, so the running time was faster. However, during turning, the running time was slower due to the decrease in speed immediately after turning.

In this study, the paddle for a swimmer with unilateral transradial deficiency to wear on the deficient side during training was designed. An experiment to acquire the swimming motions of a swimmer with unilateral transradial deficiency was conducted and the swimming motions without a paddle were analyzed using the swimming human simulation model SWUM. As a result, it was found that the contribution of the deficient limb to the thrust generation was only 16 % for the crawl and 12 % for the backstroke, respectively. Based on these results, the definition of appropriate load was newly proposed focusing on the increased rate in torque at the right and left shoulder joints. A parameter study to obtain the appropriate load was conducted with respect to the length and angle of the forearm part of the paddle, assuming the paddle size. The designed paddle will be produced and an experiment to evaluate it will be conducted in the near future.

The number of elderly dementia patients is increasing year by year and has become a social problem. As the symptoms of dementia progress, the physical functions of the patient deteriorate, leading to a vicious cycle of reduced physical activity. However, in the case of mild cognitive impairment (MCI), half of the patients with dementia can recover to normal with treatment. Therefore, early detection of dementia is essential. Therefore, we focused on gait disorder, which is one of the symptoms of dementia. As an experimental method, we conducted a walking experiment using insoles with pressure sensors placed in them. Three cognitive estimation parameters were extracted from the obtained foot pressure data. In addition, the Hasegawa dementia scale-revised (HDS-R) was used to measure the cognitive function of the subjects. Multiple regression analysis and binomial logistic regression analysis were performed to examine the relationship between cognitive function and cognitive estimation parameters. The results showed that a highly accurate cognitive function estimation equation was obtained in the group of MCI. In addition, discriminant equations were obtained with high accuracy for normal and MCI, and for dementia person and normal with MCI. This study enables us to confirm the decline of cognitive function from walking behavior during activities of daily living and may be useful for early detection and treatment of dementia.

We investigated the inertial coordination in stair descending with different inertial forces, supposing the situation that a person wears a wearable machine. We observed five healthy adult males walking with varying mass load and cadence, and analyzed their gait and closeness to inertial movement based on a kinetic energy metric. The results illustrated that the inertia harmonization appeared in common before the heel contact of swing leg and the time duration was at most 20 % time of a step in the all subjects and the all mass-load & cadence conditions. Moreover, the trunk anteflexion of 5 deg contributed to the improvement of the inertia harmonization in mid-swing phase and terminal- double-stance phase.

For evaluating the motor function of the elderly and performance of athletes, we have proposed a system that simultaneously measures the leg position and ground reaction force by fusing a laser range sensor (LRS) and instrumented insoles. However, the system had a problem that the leg position was lost when a few sampling times having occlusions. Therefore, this study proposes a method to compensate for the occlusion using machine learning. First, the system tracks legs during straight / turning walking using two LRS without a blind spot in advance. The relationship between the leg trajectory and the direction of the velocity vector in walking steps, which is identified by the insoles, is then learned using Gaussian mixture models for each type of walking. Finally, the system tracks legs using a single LRS and the insoles. When the occlusion occurs, the direction of the velocity vector is estimated through Gaussian mixture regression using the leg trajectory until the previous sampling to compensate for the current hidden leg position.

Motion analysis is important in the field of sports and rehabilitation. The optical motion capture systems that are mainly used in motion analysis are expensive and have a limited range of measurement range. In previous studies, we have proposed a method for estimating joint torque in flexion and extension using a wearable motion sensor and a force plate. However, the result by proposed method was included the error more than the result by the optical motion capture method. In the measurement of a person walks, the vibration of the body and clothing caused by the impact of the foot on the ground is the error factors. Therefore, we proposed a method to reduce noise by using a vibration model considering the vibration caused by the shock in this study. The wearable sensor system was used to measure a 5-meter straight-line gait, and the effect of the roll angle pitch angle vibration was reduced by using the proposed model consisting of the spring and damper elements. It is possible to improve the performance of the posture estimation method by using this method.

This paper proposes the estimation method of rotational axis in figure skating jump using inertial sensors. The estimation method of rotational axis consists of components centrifugal, tangential and gravity accelerations and relationship between angular velocity and combining angular velocity, and this method estimates the pitch and yaw angles to the sensor coordinate system from the axis coordinate system and the roll and pitch angles to global coordinate system from the sensor coordinate system. We conducted the measurement experiment the triple flip jumps and the quadruple salchow jumps by the high-level figure skater using inertial sensors, and we estimated the rotational axis in the triple flip and quadruple salchow jumps. These results indicated the change of rotational axis during jump, and we indicated the difference of characteristics by the difference in success of jump.

The purpose of this research was to examine how a sprinter's body orientation adapts during the approach phase to bend section of different curvature radius. When they approach bend section of different curvature radius, it is assumed that the impulse of the ground reaction force of lateral component is changed at either of right or left contact phase. Similarly, their body orientation should be appropriate at a touchdown. The authors conducted an experiment to obtain five collegiate sprinters’ kinetic and kinematic parameters using 50 force platforms and the motion capture system during the approach phase to bend section of different curvature radius (radius:38.3m and 46.74m). As a result, the impulse of the ground reaction force of lateral component was changed at right contact phase during the approach phase to bend section of different curvature radius. Furthermore, their body orientation was changed at right foot touchdown. In conclusion, when they approach bend section of different curvature radius, they are likely to accommodate the impulse of the ground reaction force of lateral component at right contact phase in order to adjust degrees of the direction change at each step by changing their body orientation at right foot touchdown.

One of the causes of running injury is the impact force at the time of landing. In particular, it has been reported that the risk of injury increases as the values of impact peak, which indicates the maximum impact force, and loading rate, increase. Therefore, it is important to reduce both of these values to prevent running injury. In response to this, we have developed a device to support the runner’s acquisition of skills to improve his or her ability to reduce landing impact by focusing on existing methods of preventing running injury as a clue for the development of the device. So we have developed two devices. The first is a forward leaning posture device, focusing on the fact that people naturally lean forward when they push an object or otherwise convey forward force to the body. The second is a foot traction device that delays the timing of landing by bringing the heel closer to the seat bone, thus preventing the foot from landing in front of the body. The results of a running experiment to investigate the effect of these two devices on the ground reaction force suggested that only the forward leaning posture device tended to reduce the impact force.

Recently, an approach for sports that attempts to support improving skills by measuring and analyzing human motions using motion capture and sensors and then feeding back the data to athletes has been generally applied. It is difficult to construct ideal motions in sprinting for track-and-field because the motions are instantaneous and complex. So, in the method using data, skill acquisition depends on the athlete’s ability. And the researches on supporting the acquisition of skills directly is still developing. Therefore, the authors focused on the effective use of the elastic function of muscle-tendon complexes and the rotation of the pelvis to promote the external rotation of the hip joint in sprinting and developed a device that provides clues to construct these motions. This experimental device promotes the effective use of the elastic function of the muscle-tendon complexes by giving elastic force in the vertical direction of the body to adjust the ground reaction force. In addition, this device manipulates the rotation of the pelvis by giving a torque in the direction of pelvic rotation to present the timing of pelvic rotation. The authors investigated acceleration when running and the relationship between the central axis of the body and the position of the feet with the device. The results suggested the tendency to increase average acceleration and run with contacting the ground on each of right and left axis.

It is known that a phenomenon in which a cardiac rhythm and a locomotor rhythm synchronization occurs during running. At these synchronizations, the cardiac rhythm rate increases in proportion to the locomotor rhythm intensity, and when it approaches the limit locomotor rhythm intensity, an unstable phenomenon of the cardiac rhythm increases becomes sometimes observed. This instability of the cardiac rhythm causes lower running efficiency, so it is necessary to keep the stable cardiac rhythm up to the faster locomotor rhythm as far as possible. It is known that the locomotor rhythm is synchronized with the musical rhythm. Therefore, we obtain a model with the musical-locomotor rhythm added to the van der Pol equation that expresses the cardiac rhythm, and we propose the musical-locomotor rhythm synchronization to suppress the instability of the cardiac rhythm for this model. By simulation, we show the musical-locomotor rhythm synchronization to suppress this instability.

For golfers, using a shaft that suits them gives good results to the shot content such as flight distance and hitting direction. On the other hand, if they use a shaft doesn’t suite them, it is necessary to adjust the movement during the swing due to the difference in sensibility. Therefore, we have developed a system that proposes the suitable shaft for golfers. The goal of the system is to propose a shaft that not only improves the trajectory but also the feeling. For that goal, in this research, we investigated how changes in shaft characteristics affect sensibility. First, we measured the swing using shafts with different kick points and calculated the deformation behavior of the shaft. Second, we classified golf swings and clarified the difference in deformation behavior for each pattern. Finally, we investigated the relationship between shaft deformation behavior and swing pattern, and considered the effect on sensitivity, so we report the details.

The purpose of this study was to quantify the swing rhythm in golf and examine how the rhythm changes in trials in two conditions; tee shots in a driving range and a course setting. The performances of 7 collegiate golfers were video-recorded by a single camera and the motions of 4 body landmarks (wrist, shoulder, hip and knee of the leading side) were represented as angles in a circular coordinate system defined for each body landmark. The times at which the angle reached 0, 25, 50, 75, 100% of the maximum angle were recorded and the time interval between them were measured for each trial to represent the swing rhythm. The results showed that each subject exhibited a unique swing rhythm with certain fluctuations and that half of the subjects used different rhythms between the driving range and course setting shots.

In this study, we tried to analyze the relationship between cooperative action of golf swing and difference of skill levels. For extracting cooperative action from different swings, we conducted experiment of acquiring swing data. Subjects was a beginner and an intermediate, an expert golfer. We measured each golfer’s swings by motion capture system (VICON). We built observance matrix from acquired positional data and we conducted singular value decomposition (SVD) on this observance matrix. By conducting SVD, we extracted cooperative action as some independent modes. Then, we compared cooperative action of different skill levels subject on main mode. As a result, we reached the following conclusion that we could indicate some independent modes shown skill levels of golf swing.

During the golf swing motion, the upper limbs and a club make a closed multi-segment loop, where it is impossible to calculate the forces and moments exerted by each hand via inverse dynamic calculation due to the kinetic redundancy of the closed loop system. An instrumented grip handle equipped with twelve sets of strain gauges was proposed and designed by the author to measure the forces and moments exerted by each hand. The purpose of this study was to clarify the validation of the multi-axial calibration method, using a force platform, for the instrumented grip handle developed for kinetic analysis of each hand during golf swing motion. A coefficient matrix, which relate the sensor output voltages of the bending strain gauges to the bending moment exerted on the location of an attached strain gauge, was identified using the information of exerting moments measured with the force platform. Crosstalk components were also considered in the calculation of the coefficient matrix. The validity of the proposed calibration method was clarified by comparing the acting forces on the top of the handle to the forces measured with the force platform. The results obtained in this study showed the errors of forces between that calculated from the instrumented grip handle and that measured with the force plate showed smaller than those obtained from the single-axial calibration method.

Walking is a daily activity, recognizing path way, space and obstacle from gaze. Looking down lead us head flexion and center of mass moves forward. The purpose of this study is to evaluate the effect of gaze position on lower limb joint angle and foot clearance during walking. 8 healthy young male participated walked at three different gaze position (front，floor, toe). 3d motion data and ground reaction force were collected, and calculated head flexion, lower limb joint angle，toe and heel clearance. In addition segment postural angle, joint angle range of motion (RoM), gait speed, stride were calculated. Analysis of variance were performed for each variable with gaze position. Head angle, head angle RoM showed significant difference between gaze position. In the stride length, when looking at the toes, it was significantly shorter than the front and floor. This result suggests gaze position does not affect kinematics of lower limb during walking, and only stride length is affected by gaze position.

Drive motion, dribbling past the facing defender is one of the most basic offensive motion in basketball. Some previous works have mentioned the important body parts for coaching drive motion as shoulder or, hand. However, they have never mentioned time series relationship between them, for example, the timing each body part start to move. Therefore, the purpose of this study is to reveal the time series relationship between body parts for drive motion. We first measured the drive motion of 6 subject divided into two groups; advanced and intermediate using motion capture (Vicon, Oxford, UK) to get the velocity data of both feet, shoulders, hands, and center of mass. Then, using the measurement data, we conducted Discrete Fourier Transformation and Principal Component Analysis in the frequency domain for each subject. From the result of the time series analysis, we could find the common pattern between the use of left foot, left shoulder, and right foot for all subjects. Also, we could find a difference in the use of the right foot and right foot between the two groups.

Although Newton-Euler method is representative one of inverse dynamics because of its convenience, inconvenient features which is called overdetermined problem have been reported. It is remarkable in the comparison of trunk torque by bottom-up approach and top-down approach. In order to resolve this problem, several methods have been proposed, and most of these methods were used by optimization of motion trajectory satisfying equations of motion. Recently biomechanical studies have been varied so that studies with a lot of force sensor have been increased. In such a situation, it is necessary to understand each force’s contribution on noted joint torque or muscle force. In this paper we propose a simple analytical formula on inverse dynamics. The methodology has two features. First feature is satisfying the overdetermined problem with low calculation cost. Second feature is perspective formula which indicates the direct relationships between each joint and each reaction force.

The purpose of this study was to quantify the functions of the support leg joints during braking phase of cutting motion int the generation of the ground reaction force. The ability of performing a quick cutting motion is an essential factor in ball sports, such as basketball, handball, and tennis. The cutting motion can be divided into two phases. One is braking phase and the other is accelerating phase. Quick cutting motion requires generating large ground reaction force in the approaching direction during the braking phase, where the force is generated by the lower limb joint torques. Participants performed a cutting motion with 180-degree turning movement and sidestep movement with different number of approaching steps. Three-dimensional coordinate data of 47 reflective markers attached to the whole-body were measured with a motion capture system with two force platforms. Dynamic contributions of the support leg joint torques to the generation of the individual components of the ground reaction force were obtained from the equation of the 3-segment multi-linked system of the support leg, where the equation of the motion was derived from the combination of the three equations of motion for the individual segments, such as the equations for constraint conditions arising from the connection of adjacent segments at joints, and the equations for anatomical constraint axes at certain joints. The result obtained in this study shows that the ankle plantar-dorsal and ankle eversion-inversion torque are main contributors to the generation of the individual components of the ground reaction force during the braking phase.

Since a secure stable measurement of ground reaction force exerted by support leg during running motion is difficult to achieve in sprint running, investigating the motion generating mechanism of running motion with use of a treadmill installed with a force platform could have a great advantage in the study of running motion from a view point of the stable measurement of 3-dimensional coordinate data as well as of ground reaction force exerted by support leg on the belt during the support phase of running. The purpose of this study were to obtain not only kinematic data of running motion but also kinetic data (i.e. belt reaction force) exerted by support leg in running, and then to quantify dynamic contributions of support leg joint torques to the generation of horizontal and vertical components of the belt reaction force. The belt tensile force was set under two conditions (i.e. low:20N, high:50N of tensile belt force) The support leg was modeled as a 3-segment rigid link model consisting of foot, shank and thigh segments. The equation of motion for the support leg model was derived from a combination of three equations, such as the equation of motion for the individual segments, the equations for constraint conditions arising from the connection of adjacent segments at joints, and the equations for anatomical constraint axes at certain joints. The result obtained in this study shows that the ankle plantar-dorsal and ankle eversion-inversion torque are main contributors to the generation of the individual components of the ground reaction force under both the belt force loading conditions.

The seated balance assessment is one of the methods to assess the degree of back pain and balance ability. Although the assessment requires measurement of the center of mass (COM) of the upper body, a method using a 3D motion analysis system is not desirable for the practical use. The purpose of this study was to estimate COM of the upper body in the seated position from data measured by force platforms mounted on seat and underfoot. To achieve the estimation, we assumed that the body consists of five segments and only the upper body has single degree of freedom. Considering the force transfer from the two force platforms, the COM of the upper body was estimated based on the equations of motion. To validate the estimation accuracy of the present method, we implemented three experiments: rest sitting, spontaneous back and force motion, and swaying by an electric cart. Comparing with the COM determined by 3D motion analysis system, fine estimation accuracy was obtained in the rest sitting and the spontaneous moiton. In the swaying by an electric cart, however, we found that the estimation error of the COM became large.

The aims of this study were to conduct finite element analysis to analyze fifth metatarsal strain distribution during soccer movements and to examine the influence of plantar pressure distribution pattern on fifth metatarsal strain concentration at the fracture site. Five subjects performed side-step cutting or cross-step cutting maneuvers. Three-dimensional foot kinematics, ground reaction force, and plantar pressure distribution were measured by using a motion capture system, force plates, and a plantar pressure sensor system, respectively. In addition, a finite element model of a foot, consisting of bony structures, ligaments, and skin, was constructed from Computed Tomography images. As the results of the simulations, in side-step cutting maneuver, maximum principal strain in the fifth metatarsal bone was concentrated from the lateral side at the fracture site. In the case of cross-step cutting maneuverer, maximum principal strain was concentrated from the plantar side at the fracture site. The strain decreased when the plantar pressure at the proximal end of the fifth metatarsal was reduced. In order to prevent fifth metatarsal fracture, a shoe design that can achieve a plantar pressure distribution that reduces strain concentration in the fifth metatarsal is required.

Pressure ulcers are caused by tissue damage, which occurs when the blood supply to an area of skin is diminished because of sustained or concentrated pressure on a patient from the mattresses of a bed. Recently, alternative pressure mattress has been proposed to prevent the pressure ulcers. This mattress uses air cells which has a slow response. This causes controlling the air cells to lag behind the change in pressure during the bed head elevation operation. Therefore, this system cannot adequately prevent the concentration of pressure on a patient. To address this issue, we need to predict the change in pressure during the bed head elevation operation and control the pressure based on this prediction. In the current work, we focus on predicting the pressure distribution. We regarded the pressure distribution as an image and predicted the change in pressure by applying a deep neural network. We evaluated the usefulness of the proposed model by experiment with 10 subjects.

Studies are being conducted to model jumping motion mechanically. Conventional studies have been conducted using only Muscle – Tendon Complex (MTC), which consists of muscle and tendon. In this study, in addition to MTC, modeling was carried out considering lower limbs including the foot, ankle joint and bone as one system. In the modeling of the system, the idea of bond graph using not only force but power was considered. So far, studies have generally been done on the idea of using the ankle as a pivot. In this paper, we analyzed the dynamic characteristics of the muscles and tendons of the lower limbs and the dynamic characteristics of the entire lower limbs during the jumping motion by the bond graph. As a result of comparing the analyzed values and the experimental values, it was clarified that the fulcrum of the foot is not the conventional ankle joint but the ball of the toe, which is a part of the toe. In addition, it has become possible to obtain the time change in tendon tension and displacement during jumping motion, as well as the discretely obtained movement velocity and power.

The purposes of this research are: Construct a musculoskeletal simulation model and calculate lower limb muscle activity and muscle force by using different types of jumping motions such as the change in initial posture and the presence/absence of arm swing. After that, the reliability and usefulness of the model are verified. This experiment is composed of a reliability verification experiment and a validity verification experiment, and each experiment is divided into two parts: a measurement experiment and a simulation. In the reliability verification experiment, SJ was performed from trials of two types of hip joint initial angles (1) Any initial knee flexion angle (Nom posture) and (2) Deep crouching posture (Deep posture), two types of arm swing motions (1) With arm swing (AS) and (2) Without arm swing (NAS) total of 4 conditions. In the validation experiment, (1) standing up from the Nom posture, (2) standing up from the Deep posture, and (3) performing a drop jump from a 38 cm. The simulation was analyzed using two models. The SJ was analyzed in two phases, the impulsion phase and the landing phase. The results of the reliability verification experiment confirmed that by using arm swing and deeper initial knee flexion angle, higher muscle activity, muscle output and jump performance was observed during SJ. Since these results are consistent with previous studies, it can be said that the model is reliable to some extent. In addition, the results of validation experiments showed that the simulation model overestimated muscle activity, but similar change curves were seen. We think that the simulation models are valid.

The existing tools to enhance jumping are mainly aimed at increasing the amount of jumping, however, in order to consider ways to develop jumping skills other than quantity, such as the direction of jumping and the way of landing, the authors focused on the human skeletal muscle arrangement itself including bi-articular muscle. We devised a method to investigate the effect of manipulating the elastic function on jumping by reconstructing the artificial muscle systems outside the body based on three pairs of six muscle systems in the thigh. Then, by arranging tension coil springs corresponding to each muscle systems, we developed a wearable mechanism that allows each tension to be adjusted freely. Finally, we investigated whether the mechanism had effects on the jumping movements by measuring the floor reaction force and joint angle.

In various sports, exerting explosive power in a short time is an important ability that affects performance. The contact mat and smartphone app measure the height of the vertical jump based on flight time. However, it has been reported that the flight time method has errors depending on the landing posture compared to the impulse method, which calculates the impulse of the ground reaction force. This study aimed to examine the effect of jump training with different feedback (jump height from impulse and flight time) on jump height and the amplitude of jump height overestimation (the difference between the jump height from impulse and the jump height from flight time). Nine participants were divided into two groups that received jump height of flight time method feedback group (FFG, n = 5) and jump height of the impulse method feedback group (IFG, n = 4). The participants started their respective immediate feedback training twice a week for four weeks. The training programs included 5 sets of 4 repetitions countermovement jump. The results indicated that comparing pre to post-measurement IFG jump height increased by 14.5% (effect size (ES) ± 95% confidence interval = 2.85 ± 2.13). FFG jump height increased by 17.9% (ES = 1.51 ± 1.44). IFG jump height measurement methods difference increased by 71.2% (ES = 0.77 ± 1.45). FFG jump height measurement methods difference increased by 215.1% (ES = 2.20 ± 1.64). these results indicate that providing flight time method was equally effective in the impulse method, but training by flight time method may have learned to movements in a way that flight time is increased.

The purpose of this study is to evaluate dynamic characteristics for sports surfaces with two-dimensional nonlinear viscoelastic model. Shock attenuation property of sports surfaces is especially important not only for the athlete’s performance but also for injury prevention. To evaluate the properties of the sports surfaces, friction tests and shock attenuation tests were often adopted to determine the horizontal and vertical characteristics, respectively. Although the diagonal impacts are often observed in athletic sports, shock attenuation test treats only the vertical impact test. Therefore, we developed a two-dimensional impact test device for examining the two-dimensional cushioning characteristics of sports surfaces in previous studies. In previous studies, we proposed the two-dimensional viscoelastic model of sport surfaces for evaluating the two-dimensional cushioning properties and indicated that the proposed model can be used for estimating the impact forces from the experimental data. In this study, shock attenuation properties were evaluated from the results of impact simulation by using the proposed model and identified parameters. Finally, the results indicated the importance of two-dimensional shock attenuation and the model-simulation method for evaluating the shock attenuation.

In this study, mechanical characteristics of carbon fiber reinforced plastic(CFRP) with thermoplastic styrenic elastomers(TPS) were investigated. The finite element method(FEM) was applied to introduced into laminated beams and numerical analysis results of the 3-point bending test were conducted to evaluate their vibration damping properties. TPS are physical mixtures of polymers, having outstanding flexibility and elasticity. They are expected to apply to the vibration damping materials for sports equipment due to good processability. The analysis result showed that, the bending stiffness was decreased by the TPS in the CFRP specimens and bending stiffness of CFRP with TPE depended on the laminated structures.

In this paper, an anisotropic hyperelastic model for artificial leather considering fiber dispersion was investigated. Fiber-reinforced elastomer such as artificial leather, show non-linear elastic characteristics, and it depends on the principle direction and dispersion of the reinforcing fibers. In this research, the fiber-reinforced structural model⁽¹⁾ was modified for the artificial leather for sports equipment. Uniaxial loading tests were conducted to observe the effect of the direction of tensile loading tests on the stress-strain relationships. The validity of the proposed model was evaluated in comparison with the experimental results. The results of the numerical analysis and the uniaxial tensile tests showed good applicability of the anisotropic hyperelastic model considering fiber dispersion in the artificial leather.

The badminton shuttlecock (shuttle) is an unique airborne projectile which has a turnover stability. The angle of attack of the shuttle changes immediately after impact. The flipping shuttle shifts to stable flight in a very short time. The purpose of this study is to investigate the turnover stability of the shuttlecock during flip movements. In this study, the flipping motion was simulated by wind tunnel experiments, and the flow field around the shuttle was visualized by a smoke-wire method and a PIV technique. The experimental results show that the turnover stability is strongly affected by the vortex behavior in the wake of the shuttlecock.

Volleyball is a sport that starts with a serve, so effective service is essential to win the game. The trajectory of the ball is complicatedly affected by the fluid force, which depends on the speed, spin speed, and panel shape. To understand the aerodynamic characteristics of the ball and to propose an ideal serve method, we measured the fluid force and flight trajectory. The fluid force applied to the ball was measured at a wind speed of 4–30 m/s in the wind tunnel. The fluid force on the ball was strongly dependent on the ball type and orientation of the panel. In the flight trajectory measurement, the trajectory of the ball was measured using a high-speed camera under controlled speed using ejection machine. The effect of the panel orientation shown by the fluid force measurement was consistent with the results of the trajectory analysis, clarifying the importance of the panel orientation in serving.

In recent ball games, fluid analysis of balls has become indispensable in terms of improving the quality of competition. Since the effect of rotation differs depending on the ball, the magnitude of the change changes even with the same drive rotation and the same rotation speed. Therefore, in volleyball, the tactics differ depending on the characteristics of the ball. The flight trajectory was measured in order to understand the aerodynamic characteristics of the ball during rotation and to propose the ideal serve method and ideal toss. In the actual striking experiment, ball ejection test was performed at a speed of 84 km / h, the rotation speed was measured with a high-speed camera, and the trajectory was analyzed with a dartfish. I was able to grasp the characteristics of the ball during rotation. In order to propose an ideal toss, we verified the trajectory during backspin and no rotation using an injection machine. From the actual hitting experiment, we were able to grasp the characteristics of the ball during rotation and expand the range of tactics in volleyball competition.

In ball games, the breaking ball is one of the elements that makes a game exciting. Among them, in soccer, a shoot that follows an irregular trajectory called a “knuckle ball” can greatly impact the outcome of the game, and such a trajectory is influenced by the number of rotations, the speed, and the surface structure of the ball. However, the mechanism of irregular orbiting has not been completely clarified. Therefore, the purpose of this study is to clarify their aerodynamic characteristics in a low rotational state by using a soccer ball. As a result, irregular orbits were observed in the range of 0.25 rps to 1.01 rps from the flight orbit simulation. But, at 1.01rps almost orbits flew in the direction of rotation due to the Magnus effect. One of the irregular trajectory is that the ball rotates weakly.

We apply the approximate Bayesian computation (ABC) method to estimate aerodynamic coefficients of table tennis ball from its flight trajectory. The ABC method replaces the calculation of likelihood function to the comparison between measured and simulated data. The drag and lift coefficients are employed as parameters, and ball trajectories are predicted with the parameters by integrating the equation of motion for a projectile. When the Euclidian distance between the measured and simulated trajectories is smaller than a tolerance, then the parameters are accepted. The obtained results are compared with those with another estimating method (interpolation method) which is formulated by the polynomial interpolation of measured trajectory data. The results of ten trajectory data are compared, and it leads to the conclusion that obtained drag coefficient shows good agreement in both the methods while the values in the lift coefficient with the ABC method are smaller than those with the interpolation method. The ABC method can successfully estimate the aerodynamic coefficients of a projectile in flight from its trajectory data. The determination of adequate tolerance in the distance function, however, remains as one of important problems.

The aerodynamic behavior of tennis balls is very complex by the surface structures (felt length, material). We carried out the flight experiment to analyze the performance of tennis balls by a pneumatic launcher machine. Two video cameras were used to measure the aerodynamics of flight tennis balls at two positions separated horizontally by about 7.5m. We proposed a new estimation method uniquely obtained from the position coordinates of the ball using the least squares method. It was found that the tennis ball was rapidly decelerated due to air resistance and that the spin rate also declined. The aerodynamic characteristics could change during the flight. The average CD of entire balls was estimated about 0.6 in both cases launched at 110km/h and 150 km/h. The average CL was also estimated about 0.25 in both cases. Compared with the wind tunnel experiment, it was found that both CD and CL of the wind tunnel experiment tended to be higher than that of flight experiment results.

The soccer ball panel pattern, which changes every World Cup, greatly affects the ball’s aerodynamics and flight characteristics. In this study, the fluid force of 11 soccer balls with different panel patterns was measured by wind tunnel tests. The drag crises with different Reynolds numbers were confirmed depending on the panel shape. To understand this, the shapes of panel grooves were measured and the relationship between them was investigated. The flow separation point was also visualized by the oil film method and the particle image velocimetry (PIV) analysis. The separation points were confirmed to be different depending on the panel groove by the oil film method in a supercritical Reynolds region. The flow separation points were found to be almost the same position in the subcritical and supercritical state and to be partly different around the Reynolds number of drag crisis.

In recent years, soccer ball panels are significantly different from conventional pentagonal hexagonal panels, and the shape and design of the ball surface have changed. The difference in panel shape has a great effect on the aerodynamic characteristics that affect the trajectory of the ball. In this study, the fluid force of 4 soccer balls with different panel patterns was measured by wind tunnel tests. No rotation and vertical rotation were measured, and the drag coefficient and lift coefficient were measured. Since the drag coefficients of the two are slightly different, it is considered that the rotation of the ball has an effect. In addition, the position of landing was measured using a soccer ball ejector. A simulation was performed using the measured values obtained by the fluid force measurement, and a comparison was made with the landing measurement by the catapult.

There are particularly interesting flights in soft tennis. There are cases where the ball flying while spinning top spins draws a parabola (normal flight) and a trajectory that extends to the back (unique flight). In the experiments conducted by the authors in the past, it was found that the rotational speed can cause negative Magnus force in addition to Magnus force. Various generation mechanisms have been considered for the negative Magnus force, but there are still many ambiguous parts. Therefore, in this study, we aim to clarify the relationship between peculiar flight and negative Magnus force by performing PIV measurement and fluid force measurement, and to supplement the negative Magnus force generation mechanism.

In recent years, fluid analysis of flight characteristics of flying discs is indispensable in competition. As a method of fluid analysis of flight characteristics of flying discs, wind tunnel experiment using wind tunnel, rotation mechanism, force detection device is mainstream. However, in that case, the influence by the rotation axis is included, making accurate measurement difficult. Therefore, in this experiment, we actually skipped the tennis ball using the injection machine and we measure the aerodynamic characteristics of the ball from the trajectory taken.

Ski jumping is a sport in which the competitor is judged based on the flight form and flight distance; therefore, ski jumpers attempt to fly as far as possible upon take-off. In general, the ski jumping suit fabric with lower air permeability is considered to be advantageous in lift generation. According to the rules and regulations for ski jumping competitions, the outstretched fabric should have a minimum air permeability of 40 L/m2/s at a water pressure of 98 Pa (10 mmAq). The purpose of this study is to investigate the effect of fabric air permeability on aerodynamic characteristics of ski jumping suits. In this study, wind tunnel experiments were carried out on an elliptic cylinder clothed with ski jumping suit fabrics of different air permeability and with two types of modified fabric made by combining different air permeability (patchwork fabric). The aerodynamic forces acting on the fabric-clothed elliptic cylinder were measured using a three component force balance. The significant lift enhancement occurs and the maximum lift coefficient shows a remarkable increase for the patchwork fabric with high air permeability placed at the front side on the upper surface of the elliptic cylinder.

For amateur tennis players, tennis balls are not consumable but durable items. Therefore, it is important to grasp the changes in flight characteristics between new and worn balls. Aerodynamic characteristics were measured in wind tunnel experiments with new balls and worn balls on two official balls that are mainly used in Japanese amateur tennis. Aerodynamic measurements were performed by the performance of the averaged amateur players targeted in this study. The coefficient of drag, C_D, was obtained from 0.7 to 0.9, but some did not change due to wear. The coefficient of lift, C_L varied from 0.05 to 0.3 and increased in proportion to the spin parameter, S_p. The flow around the spinning ball was also visualized by PIV measurements to understand the effect on aerodynamic performance. A correlation was found between the drag coefficient and the range of wake by PIV analysis. Regarding C_L, there was no difference in the value of C_L and the streamline direction between the new and worn balls. Still, the vortex generated behind the ball was different, and streamlines confirmed the difference in C_D. Also, simulation of flight trajectory prediction was performed using the fluid force measurement results by the wind tunnel experiments. Although there was almost no difference in the flight trajectory of the new balls, the flight trajectory of the worn shots was different due to the change in aerodynamic characteristics caused by the difference in felt deterioration. The flight performance due to the deterioration of the ball was confirmed, and it was found that the difference varies depending on the ball manufacturer.