Current curling AI often learns from results obtained by simulation, while there are no examples using match data obtained from real matches. In this paper, we describe an idea for building a curling AI that selects shots using real match data.

In curling, strategy is as important as the technique of throwing stones to the desired spot. To evaluate this strategy, a platform called Digital Curling exists that simulates curling on a computer. It is expected that the strategy tested in the simulator will be applied to real curling, and research into curling AI is actively being conducted. In this research, we created a curling AI using this digital curling platform. The proposed model uses a neural network as a position evaluation function to predict the winning rate. In previous models, neural networks were trained with the aim of maximizing the score at each end, and thus cannot make the optimal prediction to win in some game situations. In the proposed model, the score difference and the number of remaining ends are input, and the learning data is also created taking these two factors into consideration. This is expected to make it possible to predict optimal winning rates throughout the game. As a result, in the last shot of the end, proposed model can predict winning rate in situation where the best move would be a blank end, which is a situation that previous models cannot predict. In future research, I would like to predict the winning rate over the entire game by having the model learn all shots from the end.

Research aimed at supporting the daily lives of the hearing-impaired is actively being conducted. However, support targeted at entertainment is inadequate. Therefore, we proposed a system to recognize sounds in the stadium and visualize them with smart glass as a method to support watching sports. However, these conventional studies were not able to obtain a sufficient accuracy in recognizing sounds of the stadium. Therefore, in this study, we propose and evaluate a new method for recognizing the sound of a stadium using a deep neural network. As a result, the proposed method showed improvement in the accuracy of sound recognition in the stadium compared to the conventional method.

For inexperienced baseball players, it is difficult to predict the landing spot of an outfield fly ball and to quickly enter the catching area. We therefore considered that catching an outfield fly ball is divided into moving to the catching area and catching with a glove, and thought that catching technique could be improved by training the moving to the catching area (catching motion). We thought that the most effective way to improve the catching motion was to use audio presentation, which does not depend on what the person is looking at and does not break the concentration on the ball. The purpose of this study was to evaluate the training system and to develop a training system for catching fly balls using acoustic instructions. The purpose of this study was to evaluate the training system and compare the audio and pitch instructions. The results showed that the catching motion to move to the catching point was improved before and after the training. In particular, the catching motion was improved for the inexperienced players. The group that received the voice instruction and then the pitch instruction in that order showed a greater improvement in scoring. There was no difference in catching behavior between voice and pitch instructions. We proposed a method of wearing VR with less burden on the neck and a safe method of using VR to understand the surrounding environment while using VR.

In recent years, wearable sensors that enable gait analysis in a living environment without using force plates or motion capture systems have been developed. We conducted gait analysis using a shoe sole sensor system with four high-capacity compact triaxial force sensors and an inertial sensor mounted on the shoe sole. The system measured and compared the magnitude and variation (CV: coefficient of variation) of foot clearance and ground reaction force for young and older adult participants while walking in a straight line under test and non-test environment. Participants walked in a "test environment" in which they were told that gait parameters would be measured, and in a "non-test environment" in which they walked as usual without being told that they would be measured. We found that the minimum and maximum foot clearances were larger in the test environment but more varied in the non-test environment for both young and older adult participants. The results indicate that the over exertion during the gait under test environment may have improved their performance. The variation of ground reaction forces was reduced under non-test environment compared to under test environment.

In Japan today, the number of patients with dementia is increasing year by year due to the aging society with low birthrate, and it has become a social problem. In the case of mild cognitive impairment (MCI), half of the patients recover normally after treatment. The physical characteristics of patients with MCI include a gait that is characterized by a gait that is unsteady and with a gait that is unsteady. In this study, we derived a model to discriminate cognitive function from waist acceleration/angular velocity information during walking. The need for nursing care is increasing significantly with the aging of the population and the increase in the number of patients with dementia, so prevention of dementia as well as early detection is important. Since it has been reported that a low percentage of REM sleep is associated with decreased brain function and increased risk of dementia, getting adequate REM sleep is an effective means of preventing dementia. Another objective of this study is to derive a model to estimate the quality of REM sleep from daily exercise intensity.

In an MCI discrimination experiment, acceleration/angular velocity sensors were attached to the waist of elderly people, and they were made to walk naturally outdoors. Parameters for estimating cognitive function were extracted from the measured data, and a discriminant model was derived using binomial logistic regression analysis. For REM sleep estimation, wearable terminals were attached to elderly people, and their sleep status and exercise intensity were measured for one month. Using these data, a multinomial logistic regression analysis was conducted to derive an estimation model. As a result, a significant model that could estimate the probability of MCI was obtained. The accuracy of the model was high at 84.7%.

In the REM sleep level estimation, a significant model was obtained to estimate whether the REM sleep level was "adequate" or "deficient" according to the average walking speed. On the other hand, it is not possible to significantly estimate whether the REM sleep level is above or below "adequate," so it is necessary to increase the number of exercise intensity parameters and the number of subjects and reanalyze the results. It is also necessary to consider a new approach to the analysis method, such as multinomial logistic regression analysis with REM sleep level as a nominal variable.

Oxygen uptake during wheelchair running has been estimated, but due to various problems, it is difficult to conduct the experiment in a real field. Therefore, we conducted a wheelchair running experiment using a bike roller. However, the bike roller stand used in the experiment did not correspond to the camber angle of the wheelchair, causing camber thrust problems. Therefore, this study investigates the effect of the angle corresponding to the camber angle of the bike roller stand on wheelchair running, and verifies the significance of the angle corresponding to the camber angle of the bike roller stand.

Although it might be thought that the control of the ball in baseball pitching is mainly controlled by the end-effector, considering the dynamics of the ball and the body, we assume that the shoulder joint primarily controls the start of ball rotation and the timing of release, as well as the speed and direction. In the experiment the ball and body movements were measured using a motion capture system and the point of application of force was calculated to clarify this hypothesis.

The control of slippage between a hand and an object is a fundamental factor to improving athletic performance in sports that require a strong grip, such as baseball. The friction between the ball and the fingertips during baseball pitching is thought to relate to pitching performance such as a ball spin rate and ball control. Previous studies showed that the pitching performance such as ball spin rate and ball control was decreased when the finger and ball was wet with water. This would be due to the reduction of friction between the finger and ball. However, it is unclear whether a slippage occurs between the finger and ball during the ball releasing process of baseball pitching. In this study, we conducted the fastball pitching experiment under different conditions of friction between the fingertips and the ball by applying water, rosin powder, and pine resin to the fingertips and investigated a slippage between the finger and ball during the ball releasing process from the ball and finger behavior based on high-speed camera images. The results indicated that a slippage occurred between a finger and ball during ball releasing process regardless of finger lubrication conditions. However, we found that a larger slippage occurred when the finger was wet with water compared to the other lubrication conditions.

The aim of this study was to investigate the mechanism of the acute effect of using a ball with a reduced moment of inertia to 75% of that of a normal hardball (MOI-75). Release and spin generation parameters were analyzed and evaluated from the data of the sensor-embedded baseball (MA-Q), which was thrown before and after the MOI-75 ball. The results showed that for pitchers whose spin rate increased after throwing MOI-75, showed not only increased moment arm length at the ball release, but also increased velocity while unchanged spin rate at the onset of ball rolling in hand. These results suggest that not only the posture at the ball release but also the motion before the ball release, especially before the onset of ball rolling, needs to be improved.

Non-trap shooting, one of the soccer shooting skill, is an important technique for shooting in the penalty area and requires a high skill level. This study investigated the kinematic characteristics of the inside kick in non-trap shooting by comparing successful and failed attempts. We found significant differences between the successful and failed attemps in the joint angle of the supporting leg and in the whole body tilt angle in the failure group before and after the ball impact, indicating that their posture was unstable. Specifically, players in the failure group had a greater anterior-posterior body tilt before ball impact, suggesting that the flexed position of the supporting ankle and knee joints influenced this. These results highlight the proper control of the whole body posture and lower extremity joints necessary for successful non-trap shooting, giving soccer player new training metheds to develop their shooting skill. We identified the skill factors that contribute to effectively kicking the ball toward the goal in soccer.

The aim of this study was to investigate which joint motions are involved in achieving the quick turning movement with kick feint motions that are frequently used in soccer games. Ten healthy male experienced soccer players performed a turning movement with a kick feint. Their movements in a three-dimensional plane were recorded using four high-speed cameras, and then we calculated the kinematics of the whole body and lower extremities. We found that subjects with higher velocity in the turning movement flexed their trunk laterally and forward more than subjects with lower velocity and rotated their upper and lower trunks simultaneously. In addition, the right hip flexion displacement during the ball manipulation was smaller with these turning movements. These results suggest that, in feinting motions involving the manipulation of a soccer ball, it is important to keep the position of the ball-handling foot in a lower position and the flexion and rotation of the entire torso to achieve a quick change of direction.

It is generally accepted that ligaments play a role to stabilize the joints by holding the position of bones. We think it has a role not only for that but also for improving the performance of sports activities by thier elasticity: outside pass in soccer, bump in volleyball, and forehand in tennis. In these sports activities, the force from balls applies to the bones in the direction which dislocates the bones. The elastic ligaments are considered to deform or oscillate, and these seem to increase the velocity of the balls when they leave. The effect of elasticity of ligaments remains to be unclear. This study aims to show that the elasticity of ligaments effects on performance of sports. In one example of sport activities, the elasticity of them has effects on the outside pass in soccer. We formed the equation of motion of outside pass and obtained the velocity when the ball leaves from the legs. As a result, spring constant of the medial collateral ligament has affects on the velocity of balls more than that of lateral collateral ligament. This result suggests that the spring constant of them is one of the elements which determines the velocity of balls in outside pass in soccer.

Heading in soccer is mentioned about its chronic injury risk over the world. HIC (Head Injury Criterion) is used to assess the risk of head impact in many fields. In this study, linear acceleration of head was measured by optical motion capture system (VICON) and Impact Monitor Mouthguard. Furthermore, to compare the measurement the linear head acceleration with two methods, and discuss the motion decrease the head impact were aim of this study. HIC and angular velocity of neck swing and head rotation were calculated. HIC was small enough to judge that the risk of a single impact was small. Results of impact monitor mouthguard was better match with correlation coefficient in ball velocity after the impact than results of motion capture. Neck angular velocity of front swing influences HIC than ball velocity according to their correlation coefficient. Therefore, neck front swing is not reasonable to increase the ball velocity.

Artistic swimming, which is also known as ‘synchronised swimming’, uses an underwater upper limb motion called sculling. We focused on the force generated by a hand motion called a flat scull. The flat scull movements produced the vortical flow and it is presumed that the synchronised swimmers utilize the unsteady fluid forces obtained by this vortex for raising the body to above the surface of the water. In the flat scull, the hand changes its velocity and angle to the flow during the motion. Furthermore, it is necessary to consider a three-dimensional unsteady flow to elucidate the phenomenon because the shape of the hand is three-dimensional. This research finally aims to investigate the three-dimensional vortex structure generated by sculling motion and clarify the relationship between effective propulsion behavior and vortex generation. In the present study, we visualized the vortical flow generated by hand during sculling.

The sport of ski jumping is judged on the basis of flight form and flight distance, and it is important to increase the flight distance to win a ski jumping competition. The fabric used in ski jumping suits plays a crucial role in achieving favorable aerodynamic characteristics. In general, ski jumping suits with lower air permeability are considered to advantage the aerodynamic performance due to high lift generation. However, the aerodynamic characteristics were improved by the fabric with large air permeability in our previous study. The purpose of this study is to investigate the effect of air permeability on the aerodynamic characteristics of ski jumping suits by using the flow visualization technique. Wind tunnel experiments were carried out on the NACA airfoil clothed with ski jumping suit fabrics of different air permeability. It was confirmed that the aerodynamic characteristics of ski jumping suits are significantly influenced by air permeability because stall delay occurs and drag decreases with an increase in air permeability.

In volleyball, the flight trajectory changes on the basis of the aerodynamic forces acting on the ball. Comparing various balls, the trajectory bends, shakes, and falls differently. This is because the surface finish of the ball, the depth of the grooves in the panels, and the shape of the panels change not only the surface flow but also the wake pattern, resulting in different aerodynamic characteristics for each ball. Therefore, ball performance research leads to the development of competitions, as new tactics are created by knowing the ball's characteristics. The serve is said to be the most aggressive play because the player can raise the toss at his or her own timing. In this study, we focus on the jump serve, which has the highest scoring rate among the serves, and obtain data from injection experiments to investigate the flight trajectory from time to time, differences in aerodynamic characteristics, and the force applied to the ball, as well as to propose a ball that best reflects the skills of the players. As a result, it was found that as the angular velocity increased, the ball landed in front of the player and the amplitude of the coefficient of lateral force decreased. The surface shape was found to be highly dependent on the flight trajectory of the ball, as the point at which the ball lands and the force applied to the ball differ depending on the surface shape.

Ballroom Dancing is performed as the concept without priorly arranged choreography prepared in advance. This requires appropriate Lead and Follow during the dance progression. The “lead and follow” has been explained literally in various manners in many books, however, not sufficient in scientific meaning. In this study a simple mechanical model is proposed as a first step of building models that can explain actual various lead and follow mechanism. One dimensional model is presented in which Leader and Follower are connected at one contact position. The constitutive relation at the contact position is expressed as Visco-elastic Voigt model. As an example of dance movement, typical swing movement by the leader is applied. The sensitivity of the follower’s response and the rigidity at the contact position are taken as the parameters. The results are presented for the parameters. Further development of the model is discussed.

This study aims to develop a portable two-dimensional impact tester for sports surfaces. In our previous studies, a two-dimensional impact tester was developed for laboratory use whose frame was fixed to the floor to counteract the horizontal reaction force. To investigate the relationship between surface properties and injuries, two-dimensional impact tests on the various installed fields are required. Additionally, to perform the two-dimensional impact tests on the installed fields without fixing the fields, the portable two-dimensional impact tester, which does not need to fix the fields, is required. This study added the dummy sensor unit to the previous two-dimensional impact tester to counteract the horizontal force. 60 kg impact weight was dropped from 55 mm on the center of the two sensor units with three initial impact angles. As a result, the vertical impact force became that of half of the previous impact tester with the same condition because the vertical impact was divided into two sensor units. Furthermore, the horizontal impact force is almost the same as the previous impact tester because the horizontal impact force of the sensor unit counteracts the impact force produced by the dummy sensor unit. The variance of horizontal maximum force increases with increasing the initial impact angle, although the variances of vertical maximum force decrease with increasing the initial impact angle. Obviously, the experiments' results from the portable two-dimensional impact tester show almost the same tendencies as the previous two-impact tester.

Curling is so strategic that it is called ”chess on ice,” and has an element of uncertainty due to the changing conditions on the ice. In this study, we implemented a client development environment in Python for digital curling, which is used to study the strategy of curling. The conventional client development environment was implemented in C++, but Python leads in terms of readability and the richness of the library for machine learning. In addition, with the version change, changes were made to the means of communication and the content of communication in digital curling. Whereas in previous versions, both server and client had to be prepared within a single PC, the new version allows communication between server and client in remote locations. Based on these changes, we implemented a development environment for the client and distributed this development environment on GitHub and PyPI. This is expected to contribute to improving the level of the thinking engine.

In sports and technology, the fusion of artificial intelligence and image processing has introduced innovative avenues to elevate performance and precision in conventional sports. Curling, distinguished for its strategic complexities, revolves around the trajectory and positioning of its uniquely contoured stones. The accurate determination of stone positions assumes a pivotal role in devising strategies and attaining favorable throwing outcomes. This study presents a foundational methodology that aims to position estimation of curling stones around house by mobile robot. The approach seamlessly integrates two key components: image recognition and interpolation, leveraging the Support Vector Machine (SVM) algorithm for stone identification, complemented by sophisticated image interpolation techniques to achieve unparalleled accuracy. We conducted trials of our method using real image data collected from curling field. Leveraging SVM enabled effective stone recognition, followed by the application of image interpolation techniques to precisely estimate stone positions, based on their shapes and relative placements. Experimental results on real data have shown the impressive performance of the proposed method. The combination of SVM and interpolated image processing has greatly improved the ability to estimate the position of the stones in the sport of curling. This method not only yields accurate results, but also opens the door for future optimization and development.

Various types of sports conditioning include manual physical therapy such as joint mobilization and massage. In this study, we focused on Touch-pressure technique, an exercise therapy that improves motor function by affecting cutaneous sensory receptors through subtle skin stimulation while moving a joint. We have developed an experimental device for the elbow joint that stimulates the skin with a wide range of intensities and flexes and extends the joint. The skin stimulator has two linear motion mechanisms: one adjusts the direction and stroke of skin stimulation by a timing belt parallel to the skin, and the other adjusts the pressing force against the skin by a ball screw. Load cell is attached to the skin contactor to measure the pressing force against the skin. The joint motion device uses servo motor to control the aluminum frame that supports the arm while holding the wrist. The effects of using this experimental device on motor function indicated that this device will contribute to research the potentials of various manual physical therapies.

Tensegrity structures have unique characteristics of lightweight, flexibility, expandability and high stiffness due to strain hardening. The idea of wearing tensegrity structures was previously devised, suggesting the possibility of assisting physical movement. In this study, we aimed to design of tensegrity structures for wearing on lower limbs to assist walking. The structures are mainly placed on the side of lower limbs, and the below-knee structure on the front connects to the side structure with tension transmission and lower limb movements enabled by designing the connector with degrees of freedom to rotate. The results of loading tests show the linearity up to specific load and no hysteresis. Additionally, experiencing wearing the structures indicate that the wearable tensegrity structures will contribute to assisting lower limb movements for walking.

In a super-aging society, including sports injuries, the number of patients with knee osteoarthritis (OA) has been being expected to increase as a symptom of locomotive syndrome. Recently, transplantation of autologous cultured cartilage has been clinically applied as a treatment for OA. However, the technique of cartilage extraction is highly dependent on the surgeon experience, it is necessary to evaluate quantitative properties of tissue function, e.g. biomechanics. OCDS has been developed to visualize tissue deformation and interstitial fluid flow in cartilage tissue under compression loading can be visualized as tomography of strain rate, making effective use of tomographic tissue velocity obtained by Doppler OCT. However, Doppler OCT with high sensitivity has difficulties in the surgical application because of the severe environment of surgical operation, especially the body motion noise. In this study, the authors propose RMA-OCDS (Robot Manipulation Assisted OCDS), composed mainly of Doppler OCT and a robot manipulator, where the arthroscopic OCT probe is nose-mounted on. This system can stably provide biomechanical function of cartilage tissue, due to 3-axis attitude control of probe to the normal direction of cartilage surface measured by a depth camera. The confirmation experiment was carried out by applying RMA-OCDS to cartilage tissue on a porcine knee joint. The incident angle of probe was converged to the target angle, successfully applying the compression load to cartilage, the spatial and temporal behavior of strain rate could be visualized tomographically. In conclusion, RMA-OCDS was suggested to be effective as an intraoperative diagnosing system for evaluating biomechanical function.

We have been studying “Hayake”, one of the Kyudo yips, by investigating motion analysis using inertial sensors and EMG analysis, and found that the Hayake is a phenomenon specific to the left hand during competition. However, the sample size is small because Hayake athletes tend to choose to retire early, and the causes of Hayake have not been fully elucidated. Further, the other reason for the small sample size is that it is complicated to attach measurement devices and reflective markers to the Kyudo player’s body. Therefore, this study aimed to develop a markerless motion capture system using OpenPose, which can estimate shooting motions and provide feedback to an athlete by using a smartphone to easily capture images of the athlete's shooting movements. As a result of this system, it was possible to extract the shooting movement, joint angles, and movement time of six sections of the "Yugamae," "Uchiokoshi," "Daisan," "Kai," "Hanare," and "Zanshin" based on the eight sections of the shooting method, which are a series of shooting movements in Kyudo. This not only provides feedback of helpful information for athletes but also improves the small sample size for research, and the obtained data can be used to develop other studies.

Sports training and rehabilitation using virtual reality (VR) are attracting attention. However, there is a problem that VR training is subject to input and visual delays due to the high processing load. It is important to improve athletic performance through training even when there is a delay. Therefore, the purpose of this study was to investigate the effects of artificially added delays on athletic performance in an environment with visual delays. Specifically, we used VR to add delayed vision, and then played VR target game under this environment to investigate the effect of delay on target game performance as a two-dimensional ball landing position with the center of the target as the origin. The experimental results showed that the delay significantly affected the performance in the x direction. In order to clarify the effect of delay on the human motor system, we conducted a simulation using a model of the human brain during target game. The simulation results showed that the experimental results were reproduced for the x direction, and that the forward model was changed by the visual delay.

In the current study, we investigated the influence of foot-floor friction to fall probability using computer simulation. Neuro-musculoskeletal models simulating gaits in a young adult, an elderly non-faller, and an elderly faller were developed by tuning neural parameters. An elderly non-faller gait model showed smaller stride length, cadence, and foot clearance, while an elderly non-faller gait model showed further smaller stride length, cadence, and foot clearance, as well as larger gait variability. To alter the foot–floor friction, we changed the maximum value of traction coefficient of the foot-floor contact which corresponds to the static friction coefficient. The young adult and the elderly non-faller gait models showed slip-induced falls only when the static friction coefficient was small. However, while the elderly faller gait model showed slip-induced falls when the static friction coefficient was small same as other models, the elderly faller gait model also showed trip-induced falls when the static friction coefficient was large. Thus, we found that, especially when gait has smaller stride length/cadence/foot clearance as well as larger gait variability which is shown in elderly fallers, the influence of foot-floor friction is significant and the higher friction is not necessarily good for a stable and safe walking.

Gymnasts use honey as an anti-slip agent in the parallel bars. The friction between the gymnast’s palm and the parallel bars is crucial for their performance. This research aimed to develop an adulterated honey with higher anti-slip performance by adding an alternative substance to the pollen grains contained in honey as the homogenate solution. The frictional force was measured by applying a surface pressure to a rubber ball in point contact with beech wood used for parallel bars and measuring the triaxial component of the force. The results showed that the frictional force varied depending on the substance mixed. The players reorganized for the different sensitivities when they examined several different substances.

Cross-country skiing skating techniques combines several types of sub-techniques such as V1, V2, V2a, Turn. If we can clarify what sub-techniques are used throughout the course to enhance the performance of the athletes, we can indicate the direction of training for each individual athlete. Using a kinematic GNSS (sampling frequency 100 Hz), we aimed to improve the discrimination accuracy of the sub-techniques of and to derive an algorithm for automatic discrimination. One adult male athlete and one middle school male athlete were analyzed during a skate-style 4.2 km time trial recorded with a GNSS attached to the skier's head. A video camera was mounted on a snowmobile and followed the athlete to detect the type and number of cycles of each technique used throughout the time trial. Based on the GNSS trajectories, different patterns of head displacement (vertical head movement and direction of movement) for each skating technique were defined. The accuracy for each technique, discriminated from the waveform of the vertical motion and the pattern of the appearance of peaks and troughs obtained from the GNSS data of the head, was 96.6.% for V1, 98.2% for V2, 97.5% for V2a, and 95.7% for Turn, and 16.7% for the others. The total accuracy rate was 97.1%. In this study, the Turn was discriminated with a 95.7% accuracy rate based on data collected from a high-precision GNSS instrument. It was found that the timing of the appearance of peaks and troughs of the waveform can be patterned by each sub-technique.

The purpose of this study was to clarify the aerodynamic effects of the posture of the following skater extending his right arm to push the leading skater in the speed skating team pursuit event. Wind tunnel experiments were conducted using two full-scale human models. The leading skater was set in the posture with Arms behind back. The following skater was set in two different postures (Arms behind back and Push with right arm). The skaters were placed in tandem at two different distances (0.8 and 1.0 m). For the leading skater, the angle of attack α was always set to 0°. For the following skater, α was set to three different values (0, 20, 40°). The results showed that at U > 14 m/s, the aerodynamic drag of the lead skater decreased as the following skater extended its right arm. At U ≦ 14 m/s, the effect of the following skater's extended right arm on the aerodynamic drag of the lead skater may be related to the distance between the skaters. The effect of the extended right arm on the following skater's drag at U ≦ 14 m/s was suggested to be related to the angle of attack of the following skater. Under conditions where the following skater's aerodynamic drag is less than that of the single skater, it was suggested that the pushing posture of the following skater reduces the aerodynamic drag of the leading skater.

In recent years, advances in measurement equipment and analysis techniques have led to research and development of form support systems for sports. However, few studies have measured curling delivery form, and it is difficult for novice players to know what changes as they become more proficient in its learning. Therefore, in this paper, as a preliminary step in the construction of a learning support system for beginners in delivery form, we investigate the differences in delivery form between beginners and advanced players using a device to measure the form and body position of curling players, and how beginners change their form in the learning process.

Disruption of coordination patterns, one of the characteristics of overuse injuries, is considered to be influenced by joint stiffness. However, it is unclear how foot stiffness affects the foot coordination pattern during running. The purpose of this study was to compare the coordination pattern of the inter-foot segment during running between groups with low and high foot torsional stiffness. Sixteen men who ran with midfoot and forefoot strike participated in this study. We simultaneously measured midfoot passive resistance torque and midfoot frontal plane motion from maximal pronation to maximal supination to calculate foot torsional stiffness. Participants ran barefoot at 3.3 ± 10% m/s on the 10 m runway and we collected three-dimensional kinematics of shank, rearfoot, midfoot, and forefoot. The coupling angle was calculated using the modified vector coding technique and categorized into four coordination patterns. Participants were divided into two groups according to foot torsional stiffness. The proportion of coordination patterns in early, mid, and late stance was compared between low and high foot torsional stiffness groups using the Mann–Whitney U test (p< 0.05). There was no difference in demographic data except foot torsional stiffness between the two groups. Sagittal midfoot vs sagittal forefoot, frontal midfoot vs sagittal forefoot, and frontal rearfoot vs frontal midfoot coordination were significantly different between the two groups. These results suggest that foot torsional stiffness influences the coordination pattern of the inter-foot segment during running. In particular, low torsional stiffness foot seems to be associated with less propulsive efficiency in mid-to late stance.

The running speed is determined by the product of the step frequency and step length. There exists inter-individual differences in step length and step frequency at a given running speed and one of the contributing factors is the differences of lower extremity joint mechanics. The purpose of this study was to investigate the relationship between the inter-individual differences in step length and step frequency, and the lower extremity joint kinetics which produce the body motion. The results showed that the runner who changed step length remarkable changed the ankle joint positive work, although the runner who changed step frequency remarkable changed the hip joint negative work. The findings provide insight into the contribution of the lower extremity joint kinetics to the individual differences in the strategy of step length and step frequency.

The purpose of this study was to examine the muscle synergy during handstand perturbed by external disturbances. Five members of a male university gymnastics club were asked to handstand on a landing mat. A series of disturbances were applied to each subject by colliding a 1.0 kg object suspended from a 2.8 m high horizontal bar like a pendulum with the lower legs of the subject. The electromyographic (EMG) signals were measured from 8 muscles during the trial and muscle synergy was extracted using non-negative matrix factorization (NMF). Two patterns of synergy were extracted: One showed the synchronized activations of the wrist flexors, posterior deltoid, and rectus abdominis, which prevented the gymnast from bending toward dorsal direction at wrist and intervertebral joints during a handstand. The other showed the synchronized activations of the anterior deltoid, posterior deltoid, wrist extensors, and multifidus, which prevented the gymnast from bending toward the ventral direction at shoulder, wrist, and intervertebral joints during a handstand. The results suggest that two antagonistic patterns of muscle synergy control the balance and posture of handstand when perturbed in the ventral-dorsal directions. Further studies are indicated to confirm these findings.

Standing balance analysis to constant frequency sway of the support surface is expected to be effective for assessing the ability to balance in a particular situation. There are two control strategies for swaying below 0.7 Hz, one suppressing the head acceleration (mode 1) and the other suppressing the relative displacement of the center of mass (mode 2). However, the details of these control strategies remain unclear. The purpose of this study was to investigate control strategies when standing on a constant-frequency support surface, and to detect which of the two control strategies occurred. Thirty healthy subjects cooperated to measure the response to constant-frequency sways of 0.25 Hz and 0.50 Hz. Considering the control target, energy consumption, and energy equilibrium, we assumed a set of evaluation functions representing the control strategies describing the two modes, and derived unknown parameters to fit the experimental results. Consequently, the theoretical values of the two control strategies are obtained, and the mode can be detected by comparison with the theoretical values. Our findings may contribute to rehabilitation and evaluation using constant frequency sway.

System identification is an evaluation approach for the human standing balance. In a previous study, we proposed an identification method for individual balance parameters based on the frequency response of the horizontal sway of the support surface, and verified the reliability of the identified parameters. However, the balance characteristics and reliability of identification may change depending on the stimulus magnitude of the support surface. The purpose of this study was to investigate changes in the balance characteristics and reliability of the identification according to changes in the sway amplitude of the support surface. Three types of sway amplitudes of the support surface were applied in the identification test for 10 subjects. By comparing different sway amplitudes using intraclass correlation coefficients, we found that the reproducibility of parameter identification decreased when the sway amplitude was small. Furthermore, we confirmed that the balance characteristics, such as the delay time and phase margin, change according to the difference in sway amplitude of the support surface. Consequently, balance identification requires a support surface amplitude of a certain magnitude, and it should be considered that balance characteristics vary with stimulus magnitude.

In this study, we tried to analyze the feature of golf swings using by singular value decomposition (SVD). For extracting cooperative action from different swings, we conducted experiment of acquiring swing data. Subjects were 2 beginners and 5 intermediates, 4 expert golfers for analyzing the swing features. We measured each golfer’s swings by motion capture system (VICON). We built observance matrix from acquired positional data and we conducted SVD on this observance matrix. By conducting SVD, we extracted cooperative action as some independent modes. In this study, we attempted to classify cooperative movements using cluster analysis, with the aim of classifying the cooperative movements of individual golfers. We then categorized the cooperative movements into a small number of groups and analyzed the swing characteristics of each group of cooperative movements.

For golfers, using the suitable shaft provided good result in the shot improvement such as flight distance and hitting direction. Golf club makers have been developing golf clubs that can launch golf balls farther and more accurately. On the other hand, golf clubs with excessive distance and accuracy may reduce the fun of playing golf, so the rules set an upper limit on golf club design values. Therefore, club manufacturers have developed a service that measures a golfer's golf swing and suggests golf clubs that are suitable for the golfer's swing. As a result, many golfers improve their shot results by using the shaft recommended by the systems. The reason for the improvement is that it affects both or either the swing behavior or deformation of the shaft when using the recommended shaft. No previous studies have investigated the relationship between golf swing motion and shaft mass change. Therefore, we focus on the effect of club characteristic changes on swing behavior, and the purpose of this study is to extract differences in swing behavior of golfers when club characteristics are changed using statistical methods. First, we measured the swing behavior of several golfers when the shaft mass was changed, and calculated the swing trajectory of the club head with the wrist position as the origin. Next, principal component analysis was performed on the swing trajectories, and statistical analysis, MANOVA and Multiple Comparison Procedure were performed on the obtained swing plane data and its normal vectors to analyze the contribution of shaft mass change to swing behavior.

The appeal of golf is not only the competition of scores, but also the feeling of satisfaction that comes from hitting an accurate shot. For accurate shots, it is necessary to use a club that is suitable for each individual swing. Just as the swing is different for each golfer, the deformation behavior of the shaft during the swinging motion is also considered to be different for each golfer. In a previous study, assuming the same swing motion, the FEM model was used to determine the difference in deformation behavior of shafts with different kick points, and the results were compared among the participants in the experiment. The results showed that the kick point at which shaft deformation increased at impact differed among the participants. However, it was not possible to extract the difference in golf swing behavior that causes the difference in deformation. Therefore, the purpose of this study is to extract the golf swing motion that makes a difference in the deformation of the shaft at impact. First, a simulation model of shafts with different kick points was constructed using a finite element model. Next, golf swing motions were measured, and the deformation of shafts with different kick points was calculated. Participants who showed differences in deformation were grouped, and singular value decomposition was performed on the acceleration and angular velocity time series data, respectively. As a result, there was a clear difference in the time series data of the first mode among the groups.

In this study, we investigated the relationship between changes in running speed and the movement patterns of the foot and three lower extremity joints (ankle, knee, and hip) during one step cycle of running. A hierarchical clustering analysis was performed using three-dimensional angular time series data of these joints at three running speeds (3.5, 4.5, and 5.5 m/s). Our results revealed that three distinct clusters of subjects based on their joint movement patterns were identified. Although Cluster1 and Cluster3 exhibited similar contact times across all running speeds, Cluster3 exhibited a significantly longer flight time than Cluster1. This suggests that the phase differences in the time series data of ankle plantar dorsiflexion angle and knee flexion-extension angle were the primary factor contributing to the formation of both clusters. In contrast, Cluster2 was formed due to the phase difference in the time series data of the plantar dorsiflexion angle and the knee flexion-extension angle between the different running speeds. These findings may have important implications for understanding the complex interplay between running speed and lower limb joint movement patterns in athletes.

It is known that a phenomenon in which a respiratory rhythm coupling with a locomotor rhythm (LRC: locomotor-respiratory rhythm coupling) occurs during running. At this LRC, the respiratory rhythm rate increases in proportion to the locomotor rhythm intensity, and when it approaches the limit locomotor rhythm intensity, an unstable phenomenon of the respiratory rhythm becomes sometimes observed. This instability of the respiratory rhythm causes lower exercise efficiency, so it is necessary to keep the stable respiratory rhythm up to the faster locomotor rhythm as far as possible. Therefore, we obtain a LRC model with a locomotor rhythm added to the nonlinear differential equation that expresses the respiratory rhythm. We consider a method of a respiratory cycle command from a cerebral cortex to suppress the instability of the LRC for this model. By simulation, we show LRC, the instability of the LRC, and the respiratory cycle command from the cerebral cortex to suppress this instability.

Increased ventilation within shoes is crucial for mitigating the rise in temperature and humidity during prolonged running such as marathon. In this study, the distribution of ventilation through the shoe-upper during the swing phase of running was simulated to identify optimal locations for ventilation holes that enhance shoe ventilation. The Arbitrary Lagrangian-Eulerian (ALE) method is employed to replicate the shoe's movement and posture during the swing phase of running. The results indicate that 1) in the region proximal to the metatarsophalangeal (MP) joint (FMP), there was a high volume of inflow from the dorsal side of the toes and a high volume of outflow from the lateral side, and 2) in the region distal to the MP joint (RMP), the inflow and outflow areas varied depending on the gait cycle during the swing phase of running, and the total ventilation volume is higher below the medial side of the first metatarsal and around the posterior part of the medial longitudinal arch. This study suggests that ventilation volume through the shoe-upper can be effectively increased by designing ventilation holes in areas with high inflow and outflow volumes in the FMP, and in areas with high absolute ventilation volumes in the RMP.

There is an issue that the accumulated errors in position by the integration of acceleration in the motion measurement using IMUs. In many cases, the accumulated errors are corrected by constraint of the initial and final states of the IMU position. However, the main physical cause of these errors is considered to be the accumulated drift due to sensor bias errors, which are usually given as bias errors in the absolute coordinate system. In this study, we developed and verified a data assimilation method to correct bias errors described in the sensor coordinate system that could not be corrected by calibration.

Measuring ground reaction forces during sports activity can reveal the technical factors involved in successful movement. Therefore, we focused on a ground reaction force estimation method using inertial measurement units to enable analysis even in environments where measurement is difficult. In this study, we measured jumping motions on land using inertial measurement units, and estimated ground reaction forces and body loads using a forward dynamics model and verified the validity of the method. In this simulation, the body motion is generated by forward dynamics and optimization calculations to match the motion data measured by inertial measurement units, and ground reaction forces, ground reaction moments, joint angles, and joint torques are estimated.

In this study, we used insoles with MEMS 6-axis force sensors to measure the forces during resisted sled sprint training. The MEMS 6-axis force sensors were placed at the thenar, the hypothenar, and the heel, and 40 m sprints were performed in various conditions: unloaded, with 10 kg sled, 20 kg sled, and 30 kg sled using the insole. The running speed decreased with increasing sled weight, and the ground contact time significantly increased with a sled weight of 30 kg. In vertical reaction force (F_z), the forces at the thenar and heel decreased at 20 and 30 kg, while the Fz at the hypothenar was almost the same regardless of the sled weight. As the sled weight increased, the braking force (F_y) immediately after ground contact decreased, and the propulsive force tended to increase. The ground contact was flat in sprinting with a high running speed, so the reaction forces came from the thenar, hypothenar, and heel. In contrast, when the sled weight was heavier and the running speed was slower, the ground contact was made only with the forefoot, especially with the hypothenar. These results showed that running form in the sled sprint training is similar to the acceleration phase in short distance running, which supports that the training has a good effect on improving acceleration skills.

The purpose of this study is to verify the validity of estimating lower limb muscle activity during sagittal plane movement using only vertical ground reaction forces (2DGRF) using a musculoskeletal simulation model, and we conducted two experiments: measurements and simulations. The data from the measurement experiment was used as input data for the simulation, and the lower limb muscle activity by the simulation was calculated. In addition, four types of sagittal plane movements (SJ, CMJ, WALK, and RUN) were performed, and EMG data of BF, RF, LG, and TA were measured and compared with the simulation results. Then, the muscle force estimated using 2DGRF and the muscle force estimated using 3DGRF were compared to verify the validity. The validation results showed that the simulation model underestimated muscle activity, but a change curve similar to the experiment was observed. And there was no significant difference between the muscle force predicted using 3DGRF and 2DGRF. The model is considered to have sufficient validity.

This paper aimed to develop an implementation for measuring the elasticity distribution on the foot sole. In advance to the human experiment, some material foams which were imitate human subcutaneous fat and muscle layers of the foot sole were examined using our implemented device and validated its elasticity. The validation result showed that the relationship between compression depth and reaction force could be expressed as two different piecewise linear approximation and its hysteresis of two-layered structure of the artificial materials. The results of human sole measurements also showed hysteresis characteristics among whole segmented small compartment areas. On the other hand, in some of compartment areas, such as edges of the foot sole or lateral longitudinal arch, reaction force could not be measured due to the slippage in the compression process. The distribution pattern of the reaction forces depended on the subject with the constant depth condition. The quantitative foot sole elasticity obtained using the proposed device may have the potential to design criteria for insoles by prosthetists and orthotist in the future.