Currently, due to the influence of COVID-19, we are forced to refrain from going out, and lack of exercise is becoming a serious social problem. In addition, the survey revealed that lack of exercise is linked to the aggravation of the new coronavirus infection and the increased risk of death due to the infection. The purpose of this study is to increase the amount of daily exercise and eliminate the lack of exercise by grasping the amount of metabolism in activities of daily living. To estimate the amount of metabolism, the time constant of oxygen uptake measured by a breath gas analyzer using a mask is required. Therefore, we are studying a method for simply estimating the time constant of oxygen intake from parameters such as the time constant of heart rate and total hemoglobin, walking speed, and body fat percentage so that the amount of metabolism can be estimated without a specialized device. In the experiment, a walking experiment was performed on 19 subjects, and an estimation formula for the time constant of oxygen uptake was derived and evaluated. As a result, we were able to derive a highly accurate estimation formula for the oxygen uptake time constant. By using the time constant of oxygen uptake estimated by this estimation formula, it is considered that the amount of metabolism in activities of daily living can be estimated with high accuracy.

River structures such as headworks installed in channels are called low-head dams. They are known to cause water accidents frequently due to the circulating flow that occurs at the downstream neighboring the weirs. In this study, the risk of drowning due to the circulating flow at the low-head dam was investigated by using a simulation model that can simultaneously solve the flow and human movement. From a series of simulation with different hydraulic conditions, it was found that the circulating flow can occur at both the surface and the riverbed, that a victim can continue to float on the surface by wearing a life jacket even if he is trapped by the current while he can be trapped by the circular current for a long time.

A human body stricken by the run-up tsunami on land were simulated with a coupled human fluid numerical model. In addition to the efficacy of lifejacket to keep the victim floating, injury risk of collision both against tsunami front and obstacles were assessed with different wave height ranging from 0.5 m to 20 m. Regardless of the wave height and wearing lifejacket, a body of victim stricken by the tsunami was swept by the edge of propagating tsunami and not swallowed into the water, clear function of lifejacket to keep a body floating was not found. Injury risk was assessed with the criterion of automobile accident that are evaluated from acceleration working on a head and chest. In the case of simple striking of tsunami against the body, risk of serious damage and death significantly increases when the wave height exceeds 10m. The simulations considering the collision to a floating steel-drum or a fixed wall showed that the risk of serious injury or death can arise even if a tsunami height is less than 1 m.

The purpose of this study is to clarify the effect of changes in surface shape due to fabric stretch of low resistance wear on fluid behavior. Three-dimensional surface texture measurement was performed to clarify the geometrical changes of the fabric, and Particle Image Velocimetry measurement was performed to clarify the fluid behavior. As a result, the relationship between fluid behavior and fabric elongation differed depending on the fabric features. In the non-urethane fabric, surface roughness increased and critical velocity decreased as the fabric stretched. On the other hand, in the urethane / dimple (outer / inner) fabrics, critical velocity was lower than the others at a fabric ratio of 95 % (fabric ratio = fabric length / fabric length when stretched).

Located in heavy snow areas, Research Centre for Winter Sports Science of Kitami Institute of Technology has been promoting the development of the design of ski boots which can improve the Japanese skiers’ speed in alpine ski competition. Previous experimental studies have shown that the large inclination angle and a fast inclination angle speed have a great influence on the improvement of downhill speed in alpine skiing^{(1) ~ (7)}. In this study, we do an indoor skiing experiment using the "SkyTech" ski simulator, examined a quantitative measurement method of the inclination angle as an evaluation parameter, and constructed a measurement environment. Furthermore, we investigated a numerical evaluation method for alpine skiing turn movements from numerical data that measured pressure fluctuations in the sole of the foot using an insole-type sensor installed in the ski boots of the subject.

This paper points out that our body movements work for holistic sensing and actuation, if we note the important role of proprioception. As the Real World is changing frequently and extensive and what makes the problem difficult in an unpredictable manner, we need to pay attention to the importance of analog, although DX is getting wide attention these days. The currently wide-used approach is based on cardinal approach, i.e., Euclidean Space approach. But when the dimension becomes very large, we cannot solve the problem mathematically based on Euclidean Space approach. The feelings of muscles or blood are analog, but if we introduce ordinal or Non-Euclidean approach, we can prioritize our decisions and act adequately. In other words, we can perceive and understand the current situation correctly, if our performance is indicated to help our Instinct. Instinct can process a large amount of analog information and in addition it can carry this task in real time. This paper points out the importance of Instinct and proposed a performance indicator to help our Instinct relating our movements. .

Sport climbing is one of the most popular sports and was adopted as a new official sport at Tokyo Olympic 2020. Players climb walls with holds in this event. Movements and postures of climbers have a tendency to become complicated compared with other sports due to a wide variety of holds and walls. Therefore, it is difficult to measure and analyze the whole body motion of climbers precisely. This paper shows multiple force sensing systems that measures the force applied to holds by climbers. A typical movement called “Dyno” is focused on in this paper. Dyno is all out leap using whole body to reach the next hold. In this paper, the dyno movements are measured by four force measurement systems incorporating six-axis force sensors. The subjects of the experiment are nine advanced and eight intermediate climbers. As a result, some differences between the advanced and intermediate climbers are shown.

In our previous study, we aimed at achieving human-adaptive vibration design in a vehicle cabin on the basis of the passengers’ sensory characteristics. To this end, the passengers’ psychological stress caused by seat and floor vibration in a commercial vehicle was analyzed. However, we measured the vibrational acceleration of each occupant by employing a vibrational acceleration sensor directly attached to the occupant’s body. Hence, there is a possibility that attaching the sensor to the occupants’ bodies induced psychological stress. Based on this rationale, in this study, we measured the vibrational acceleration of an occupant’s body without attaching a sensor by incorporating a non-contact measurement method. We employed a laser displacement sensor for measuring the vibrational acceleration of the occupant’s body because such a sensor has higher temporal and spatial resolutions. We simultaneously measured the displacement of the occupant’s body and the corresponding vibrational acceleration of the laser displacement sensor. Subsequently, we estimated the vibrational acceleration of the occupant’s body by incorporating the difference between the second derivative of the measured displacement with respect to time and vibrational acceleration of the sensor. The obtained results indicate that within a low-frequency range, the estimated vibrational acceleration of the occupant’s body is nearby identical in value to that of the previous vibrational acceleration sensor, which was directly attached to the occupant’s body.

The purpose of this study was to clarify the effect of the foot strike patterns when the running speed changes and the swing leg movement, and to examine the relationship between the foot strike patterns and the swing leg movement. Participants were 11 male general university students. Seven levels of subjective effort were set, and each set subjective effort was sprinted once. Leg movements and foot strike patterns were investigated using a digital camera and an F-scan sensor sheet inserted into the shoe. As a result, the magnitude of the relative running speed was considered to vary from subject to subject. Foot strike patterns were many Rear Foot Strike regardless of the speed of running, but when the running speed increased, some people were Fore Foot Strike. The subjects in this study had a small relative movement of the knees and toes from the time of swinging to the time of landing even if the running speed changed, and the relative position of the toes in the vertical direction at the time of swinging was upward that it was thought that this led to the Rear Foot Strike. On the other hand, some subjects increase the relative movement of the knees and toes from the time of swinging to the time of landing when the running speed increases, and the relative position of the toes in the vertical direction at the time of swinging was down that it was thought that this led to the Fore Foot Strike.

This paper aimed to examine error factors from the perspective of the conservation law of the angular momentum when a rigid body model is used in sprint running. Firstly, sprint runs were measured using a motion capture system and force platforms. This experimental result showed that the angular momentum vector was not conserved during the flight phase in sprint running. Also, each segment's length was not constant. This result contradicted the prerequisite of the rigid body model. On the other hand, a high stiffness pipe colliding with the force platform was captured using a motion capture system and a force platform. The pipe's angular momentum vector was accurately conserved during the flight phase. Therefore, the modeling error of the rigid body model by deformation of each segment could mainly cause the angular momentum vector not to be conserved in sprint running.

One of the factors causing running injury is landing impact. Suppression of the maximum value of impact force in the vertical direction (IP: Impact peak), and the loading rate (LR), is considered to reduce the risk of running injury. We focused on the phenomenon that the landing impact is reduced by the forward leaning posture and investigated the method to support the adjustment of the anterior pelvic tilt and the trunk inclination by using the device. Therefore, we devised an idea of providing tensile force around the pelvis angle to make it easier to perceive the difference in muscle and skin changes and by providing sound according to the trunk angle. Based on this idea, two types of devices were constructed experimentally: a pelvis angle adjustment support unit that provides tensile force by a tension spring attached to the sternum and sacrum according to the forward tilt of the pelvis, and a trunk angle adjustment support unit that generates an adjusting sound that changes according to the trunk angle with using an inertial sensor. As a result of running experiments to investigate the effects of these two devices on pelvic and trunks angles and landing impact, we found that the devices will support forward tilt on pelvic and trunk angles.

Because foam materials are often used as the midsole part of various sports shoes because it affects the movement of runners, mechanical design method of the midsole is important for modification of their performance. Then, this study aims to develop the designing method of running shoes by analyzing mechanical behavior of their midsole. Particularly, dynamic deformation behavior of the midsole is analyzed by modeling microscopic structure of its foam materials. In this modeling, 14-sided Kelvin cell is used in finite element method for construction of membrane geometry. And then the behavior of cyclic deformation in this model of foam structure is analyzed for the investigation of foam dynamics.

In playing the golf, using suitable golf club is important to put out high scores and hit the correct shot. Several studies have been conducted on good club choice and improved golf club performance. A good choice of golf club not only improves the shot, but also improves the feel. However, few studies have investigated the effect of changes in the physical properties of the club on the feel. Therefore, this study aims to clarify the factors that influence the feel when golfers swing shafts with different kick points. First, a golf club was modeled by a simulation model consisting of Euler-Bernoulli beams in order to calculate the deformation behavior of the shaft. Next, we performed a motion capture test to measure the grip movement of shafts with different kick points. We calculated the inertial force generated at each node from the measured grip movement and calculated the bending behavior by inputting it to the simulation model. Then, using the calculated bending behavior as an observation matrix, singular value decomposition was applied, and the main deformation behavior was calculated and compared. Finally, we were able to find common ground among testers who prefer high-kick points and identify behaviors that affect the feel.

The surface of a golf ball is provided with innumerable dents called dimples to improve the flight distance. I think that these dimples can show the state by the dimple surface occupancy and the dimple volume ratio. Therefore, we will manufacture a model ball in which the dimple surface occupancy is changed by the dimple diameter and the number of dimples, and the dimple depth is changed to change the dimple volume ratio. Using them, we will carry out a lift and drag measurement experiment by a wind tunnel experiment. Then, a flight trajectory simulation was performed based on the obtained experimental results, and it was clarified how the dimple surface occupancy and the dimple volume ratio affect the flight distance.

Playing positions play an important role in football. Players are positioned closely during defense and widely during attack. Previous investigation has demonstrated that the surface area of the field players (SA) depends on the playing situation (PS), such as attack or defense. We hypothesize that SA is also related with the playing area (PA). The present investigation examined the influence of PS and PA on SA in a professional football match. We used 10 Hz GNSS units to monitor the ten field players in the first half of the ten official matches of second-division Japanese Professional Football League. PS was evaluated as attack or defense, while PA was divided into three areas based on the centroid position. The 2-way ANOVA test showed significant interaction of PS and PA with SA (p<0.001). The significant difference in SA between PS’s depended on PA and was limited to the first and second tertile from the players’ own goal area. Thus, the investigation suggests that SA depends not only on PS but also on PA.

The University Sports Association will be established in 2019, and the competitive power of university sports is expected to be further improved. In particular, volleyball is expected to win a medal in the Olympic Games, and research to improve its technical performance is being actively conducted. In volleyball, it is necessary to quickly position oneself at the point where the ball falls and to block the opponent's spikes. However, it is difficult to predict the play in advance. In this study, We use deep learning to analyze game footage to predict the course of spikes and the optimal blocker and receiver positions according to the game situation and team, and verify plays that directly lead to scoring.

In recent years, with the increase in the number of people playing sports, the number of accidents during competitions has been on the rise. Baseball is one of the sports in which players are exposed to shocks, and dead balls to the head can lead to concussions and fatalities. Thus, a human safety evaluation using numerical simulations toward the injury prevention is highly demanding. In this study, a Hybrid III human dummy model and baseball impact analysis were performed to investigate how the ball impact location and angle affect head injuries. Our simulations show that the peak value of the brain injury criteria BrIC and its time profile are strongly affected by the baseball impact angle. In particular, the trend is significant in case of the frontal head-to-baseball impact.

The purpose of this study was to verify the effect of applying nail protectors on the throwing motion and to improve the throwing performance. Three male handball players(19.67±1.46y, 174.67±5.51cm and 72.67±5.03kg) who played at Division 1 Tokai Student Handball organization participated in this study. At the first, throwing motions were recorded by the three-dimensional motion capture system(200Hz) in order to reveal the difference of throwing motions while applying the nail protectors and not applying them. At the second, subjects wore surface myoelectric potential sensor at two locations of muscle activity in two conditions. As the results, in the analysis of the throwing motion it was revealed that the external rotation of shoulder while applying the nail protectors showed significantly greater ROM than while not applying them at the moment of the Stride Foot Contact as the result of analyzing the series of the throwing motion on each phase. Besides, the analysis of surface myoelectric potential sensor revealed nail protector change the muscle activity of Brachioradialis extremely. For these reasons, applying nail protector can improves the throwing performance and the pronation of forearm at the release of the ball.

The purpose of this study was to investigate the effect of nail protector to the sequential jump performance. It was obvious that putting the nail protector on to the nail prevents the nail bend in our previous studies. Although the protector prevents bending the nail, it was not clear that how it affects to the performance or why? It was not sufficient evidence so far. Therefore, the effects of putting the protector to the nail should be consider for improving the performance in sports activities. Five male subjects were performed sequential vertical jump under maximum effort. Vertical ground reaction force, biaxial strain of foot thumb nail and foot middle fingernail on both sides and 3-dimensional position of hip, knee, ankle, heel, toe were measured by force plate, biaxial strain gage and 3-D motion capture system simultaneously. From these data, floor contact time, jump height, knee angle during contact phase, strain of nails were calculated by each jump in order to consider the relationship between the nail protector and there elements. Finally, one subject who performed with different manner of jumping from the others shows the significant relationship between the nail protector and the performance, the contact time. It means that the contact period shows the significant shorter when the nail protector was put on the nail despite the jump heights did not show the significant difference. In other words, the subject could perform the same task with shorter time.

We present one estimation method of the aerodynamic coefficients and the axis of rotation of a ball in flight from the trajectory data of the ball. In this method, local geometrical quantities of a spatial curve obtained from the trajectory are related to fluid forces included in the motion equation of the ball. The purpose of the present study is to clarify the unsteady aerodynamic forces acting on the ball via the analysis of the flight trajectory-based estimation method. In order to confirm the accuracy of the estimation, sample trajectory is used, which is simulated by giving the aerodynamic coefficients and the rotation axis. The estimated results are in sufficient agreement with the given conditions. Also, the present method reproduces the aerodynamic coefficients and the axis of rotation from three-dimensional trajectory measured with golf ball. In this estimation, the accuracy is improved by using the interpolation of velocity data, and the results show smooth variation in the aerodynamic quantities. In particular, it is found that the acceleration and/or deceleration in the ball motion affects drag more significantly than the Magnus force. Moreover, we estimate the aerodynamic coefficients from two-dimensional trajectory data of three types of golf ball with different specification. The results clarify the effect of the specification to the aerodynamic coefficients, and this fact support the validity of the present estimation method.

In the recent study, it was revealed that the throw trajectory is changed by speed, number of revolutions, rotation axis degree, the seam shape of the ball surface. We carried out the pitching experiment to the clarify the influence of tilt of ball , speed and number of revolutions to the trajectory of the ball. The pitching test was carried out by 12 pitchers of the baseball club in the university. The IoT ball is used to measure speed, number of revolutions and tilt of ball. Pitchi a ball photographed it using a high-speed camera. In addition, we measured the lift coefficient and drag coefficient at the time of pitching by fluid force experiment. In the fluid force experiment, 1-Seam, 2-Seam, and 4-Seam measurements were performed to see the difference in seams. As a result, it was found that the pitching trajectory changed laterally depending on the degree of the rotation axis. Furthermore, the change of lift and drag coefficients with the change of rotation speed for ball of 1-Seam, 2-Seam and 4-Seam was clarified.

In the recent study, it was revealed that both feather ball and nylon ball have a higher drag coefficient when rotating with and without rotation, and that the nylon ball has a higher drag coefficient than the feather ball. In addition, in the flight trajectory verification experiment, the deceleration rates of the feather ball and nylon ball during rotation are compared at the initial and final speeds. It was clarified that the deceleration rate of the nylon ball was higher than the feather ball in 2 out of 3 subjects. The drag coefficient at 200 km/h or higher are not clearly proved yet. Therefore, in this study, the deceleration rates of the initial and final speeds of the feather ball and nylon ball are calculated in the flight trajectory experiment, and the aerodynamic characteristics of the shuttlecock in the high-speed region are further elucidated. As a result, the results showed that the feather ball had a higher deceleration rate than the nylon ball in both subjects, but there was no significant change in the deceleration rate values. The drag coefficient tends to decrease significantly with the decrease in speed in the range of 200 km/h or more for both the feather ball and the nylon ball.

We used a Magnetic Suspension and Balance System (MSBS) in order to make accurate measurements of the Magnus force acting on a rotating sphere. The MSBS levitates the model by controlling the magnetic forces using electromagnets. Since the model is levitated by the MSBS, there is no support interference. We succeeded in measuring the Magnus force on the rotating sphere without the use of a physical support. It was measured that the Magnus force coefficient increases with increasing the spin parameter.

The conditions for the generation of negative Magnus force about a rotating sphere has not been clarified yet. Therefore, we developed a wind tunnel test method to investigate the negative Magnus force region using the 1-m magnetic suspension and balance system of the Institute of Fluid Science, Tohoku University, which can support a model in the wind tunnel test section by magnetic force without a mechanical support. By constructing a sensing and control method and a model structure suitable for a rotating sphere, we obtained a technique to rotate a sphere of about 142 mm in diameter to about 1100 min-1 with magnetic support. By applying this technique to a wind tunnel test, it is now possible to acquire the aerodynamic forces that change from time to time with decay of rotation speed from 560 min-1 in an airflow of 7 m/s. This corresponds to a Reynolds number of about 6.5×105 based on the diameter of the sphere model, and a ratio of the circumferential velocity of the rotating sphere to the mainstream velocity, SP, varying from 0.6 to 0. In the present wind tunnel test, the normal Magnus effect was observed, and in the range of 0.5 < SP < 0.6, a decrease in the positive Magnus force and a behavior like approaching the critical region were observed, but the negative Magnus force was not observed. The aerodynamic force evaluation was limited to qualitative evaluation due to the large fluctuation of aerodynamic force that may be caused by the change of the model outline with rotation and the center-of-gravity misalignment.

Volleyball is a sport that starts with a serve, so effective service is essential to win the game. he trajectory of the ball is complicatedly affected by the fluid force, which depends on the speed, spin speed, and panel shape. The ball of volleyball is changed every Olympics, and Mikasa's V200W and V300W are used in volleyball competitions. The difference is the way of processing, and we believe the winkle patterns which made physically has an effect on the aerodynamic properties of the ball. The surface roughness of each ball panel has significant effects on the flight trajectory, which influences the content and tactics of the game. In this research, we measured the change of the force applied to the ball when it is not rotating, and quantified the variable velocity range. By understanding the hydrodynamic characteristics of the ball, we aimed to obtain datas for the product development of balls, and the improvement of coaching ability.

In recent ball game sports, the shape of the ball changes with each tournament, and the content and tactics of the game also change due to the great influence on the trajectory of the ball. Ball fluid analysis has become indispensable. Even in volleyball, various ballistic changes can be seen because the ball flies while rotating. And volleyball play begins with a serve. Serve is said to be the most aggressive play because you can raise the toss and hit at your own timing without being disturbed by anyone. Therefore, in this study, we focused on the jump serve of volleyball and compared it with existing balls. Therefore, the flight trajectory of the ball and the force applied to the ball were measured from the actual hitting experiment, the injection experiment, and the wind tunnel experiment. From there, the flight distance and speed change were predicted. From the results, it was confirmed that the flight distance became shorter as the number of revolutions increased in all the spheres. In addition, the panel shape, the difference in surface shape is, it was confirmed that a significant impact on the trajectory. Based on these results, we propose a jump serve that can be dropped in front of the apparent flight trajectory.

The design of soccer balls continues to change at every World Cup. In addition, the panels of soccer balls in recent years are significantly different from the conventional panels composed of pentagons and hexagons, and the shape and design of the surface of the balls have changed. Therefore, various aerodynamic studies on soccer balls have been reported. The difference in panel shape has a great effect on the aerodynamic characteristics that affect the trajectory of the ball. There are many research results on aerodynamic characteristics of soccer balls, but the relationship between fluid force and grooves has not yet been clarified. In addition, all visualization experiments are supercritical Reynolds numbers, and the visualization of surface shapes such as the flow around the ball and dimples at the Reynolds number where drag crisis occurs is not yet known. Therefore, in this study, we investigated the difference in aerodynamic characteristics for each soccer ball panel and confirmed the relationship between the groove shape and the drag crisis. In addition, in order to clarify the cause of the Reynolds number at which drug crisis occurs depending on the panel shape, we performed oil film experiments and visualized the peeling point by 2D-PIV measurement.

This research is related to the tools used in the paratriathlon. The paratriathlon is a sport where strategy and experience are greatly influenced by the characteristics of the activities performed throughout the three competition events. Moreover, since many tools are used in the game, they are considered part of the competition. This time, we focused on the development of equipment related to the Bike event (hand bike), which accounts for about 50% of the competition time and has a major impact on winning and losing. Foot placement is very important for athletes with lower limb motor disfunction. Therefore, a foot support that can be operated as much as possible using the entire sole is desired. However, if the design change makes it possible to operate using the entire sole, the shape of the foot support (Prototype) may increase the air resistance, because the front projection area increases. Therefore, we have developed a foot support that minimizes the forward projection area while obtaining stable operability. In this study, we measured the air resistance of the Conventional-type and the Prototype equipment to better enable them to be operated with the entire sole.

Recently, in the field of sports, there has been a lot of research on the use of wearable sensors to analyze the movements of athletes and utilize them for training and coaching. However, there are a few studies on wheelchair sports. The purpose of this study is to propose a model for estimating the vehicle speed when driving a wheelchair-using wearable sensors, and to easily realize the measurement of a player's movement using wearable sensors. The proposed model uses LSTM to estimate vehicle speed based on the angular velocity information of the arms. One sensor was attached to each of the subject's upper arm and forearm the accuracy of the proposed model was evaluated through six different motion experiments, and it was confirmed that the model could be estimated with a root mean square error of 0.421 m/s ± 0.078 m/s in the best case.

Wheelchair basketball (hereinafter called WB) is one of the major disciplines of parasport. WB is a game won by the team that has scored at least one more point than its opponent at the end of the game, and the shooting that goes into scoring is one of the most important elements of the game. This study aim is to clarify the characteristics of shooting motions in WB by focusing on trunk movements, which have not received much attention in previous studies. The subjects were four students who were able to move their trunks voluntarily in WB class 2.0 or higher. Seat pressure distribution (hereinafter called SPD) was measured using SRSoftVision (SumitomoRiko Co. Ltd., Aichi Japan) and surface electromyography was measured using PolymatePro (MiyukiGiken Co. Ltd., Tokyo Japan, MP6000). In the experiment, the subject made 50 two-handed shots from the front of the goal with the tip of the wheelchair aligned on the free-throw line. The points where the shot flew were recorded in ten sections, including the ring, based on the inner rectangle of the backboard. The results of SPD and surface electromyography were evaluated using the seat center movement and integral electromyography. The results showed that when the shoot reached the height of the window, the instantaneous movement of the seat center in the X-coordinate was larger and the movement in the Y-coordinate was smaller than when the shoot did not reach the height of the window, and the muscle activity of the latissimus dorsi and rectus abdominis tended to be higher.

The Heel turn is a figure which represents the characteristic feature of international style ballroom dancing. The heel turn is mechanically analysed in the present study. The natural turn and the reverse turn in Foxtrot are taken as the representative example of the heel turn. The natural movement of dancers’ motion is represented in the analysis by assuming the continuity of the curvature of moving path and the velocity of dancers. The movement of each dancer as well as that of the couple centre, and the rotation of the couple, rise and fall, the sway are obtained by the analysis of these figures. The difference between the natural turn and the reverse turn is discussed to explain the actual feeling difference of dancers.

The purpose of this study was to focus on the lower limb joint angles and lower limb joint moments of ballet dancers during right and left grand jeté landings, and to compare the right and left differences from a kinetic perspective. Fifteen female professional ballet dancers agreed to experiment condition participated as subjects.

There were no statistically significant differences in the angles and moments of the lower limb three joints at the max FZ and the max moment of each joint during landing. It is conceivable that professional ballet dancers had equal grand jeté landings on both sides, although there were differences in physical characteristic and other factors between the left and right legs. In addition, during landing, the max moment of each joint peaks before the max FZ. It is thought that ballet dancers descend from jumps with their bodies as stretched as possible.

This study aims to investigate the mechanism of Bhavsar performance of parallel bars in artistic gymnastics. The authors focused on the Bhavsar's specific motion after its release which has a forward rotational motion during the flight phase. The authors conducted an experiment to obtain kinematics of Bhavsar performance using an optical motion capture system with a high-speed camera. The results show that the subject's center of gravity deviated after its lowest height timing and had a maximum forward velocity peak. The negative moment around the center of gravity can be seen slightly before the lowest height point. It was caused that the moment arm of the force vector pointed out backward from the force vector acting at the contact point of the hand. This vector angle configuration makes the negative angular impulse which must be necessary prerequisite for the forward rotational motion after his release.

“Compete” or “Challenge” is the key word for the current sports. But in the old days, we enjoyed sports by our own way as we like. We watched someone playing and when it looked so exciting, we joined him or her. We made friends this way. We enjoyed life together. On the other hand, the current sports emphasize competition. The current sports are important from the standpoint that they satisfy our basic human needs. But if we remember that sports are physical activity and such analog elements as blood, muscle, etc. (motor movements) play an important role for holistic sensing and actuation, we should look at sports from another angle. This is nothing other than the nonverbal world and that is why sports in the old days fascinated us and led us to making friends. It is pointed out that now we should look at sports from the perspective of old days and restore them in the new way to enjoy our life.

To improve the competitive performances of tennis players, we investigated the relationships between the ball hit sounds during serving and serve directions. From measurements of the hit sounds produced at a tennis court by multiple subjects, it was observed that there were differences in the sound frequencies around 1 kHz depending on the serve directions. Further, based on investigation of the position from which a subject hits the ball with a racket, the hit position was observed to differ according to the serve direction. When directing the serve towards the center of the court, the hit point was concentrated on the center of the racket; however, when directing the serves over a wide range of angles, the hit points were concentrated at diagonal positions 45°above the center of the racket. In addition, it was clarified that differences of the racket frame, thereby causing the differences in the hit sounds noted previously.

The purpose of this study is to propose a two-dimensional dynamic force reduction (DFR) value for evaluating the shock attenuation properties of synthetic turf with spike stud. In general, shock attenuation properties are evaluated with force reduction (FR) value calculated from the maximum force onto the concrete and turf only in vertical direction. Meanwhile, actual sports activities have a wide range of impact angles and intensities. For this reason, a two-dimensional impact test device with angle sensor was developed to measure not only for the vertical impact force but also for that of horizontal direction. Additionally, spike studs were attached to the bottom of the sensor unit avoiding the uncertainty of data caused by unevenness of the surface. In conclusion, two-dimensional DFR (dynamic force reduction) values are calculated from time series force and angle data. Although the uncertainty in measurement still remain especially in low angle, the appropriate evaluation of shock attenuation was obtained by this method.

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, some sport governing bodies often adopt friction tests and shock attenuation tests 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. To produce a simultaneous two-dimensional force against a test specimen, we incorporated a parallelogram linkage in the measuring system. In this study, impact tests were conducted using spike pins for long-distance running race, assuming the actual use of sports surfaces. The test specimens were three types of urethane materials with different hardness. Five different initial impact angles and seven drop height impact tests were performed to each specimen. Two-dimensional impact force and acceleration were obtained from two load cells and an accelerometer, and deformation was calculated from acceleration by time integration. According to the impact force and deformation waveforms, it was confirmed that the shock attenuation in the horizontal direction does not depend on that of vertical direction. In addition, focusing on the maximum deformation of each surface, the difference between specimens were observed in two-dimensional shock attenuation as well. From these results, it is inappropriate to consider only the vertical direction when evaluating the shock attenuation performance, and the evaluation of the shock attenuation in the horizontal direction should also be considered.

Decision-making process is one of the most critical aspect that determines athletic performance. However in real-world measurement, it is not easy to analyze decision-making independently because many other aspects potentially include athletic behavior. We have established a virtual reality (VR) environment which can allow us to manipulate visual conditions with sufficiently realistic sports senario. In this study, we used a VR system for baseball hitting to examine how the batter’s prediction of the pitched ball type based on pitching form information affects their decision-making and corresponding batting action.

We formulate the acceleration at any point in a rigid body in translational and rotational motion in order to analyze the sensor output of a baseball-type accelerometer which consists of one sensor for low acceleration and three for high acceleration. On the basis of this formulation, we develop a simulator for the sensor outputs, and in particular this simulator includes the effect of temporal change in the angular speed and the axis of rotation. Comparison of simulated outputs with sensor outputs measured in flight experiments shows that the axis of rotation is moving slowly during its flight. Also, in order to estimate the aerodynamic force on the ball-type sensor, the translational acceleration along flight trajectory is investigated numerically by integrating the motion equations of the ball-type sensor. In the parameter study with the drag and lift coefficients, it is found that the amplitude and phase in the sensor outputs are affected in according to the aerodynamic coefficients. Furthermore, we attempt to estimate the aerodynamic forces acting on the ball-type accelerometer with the translational acceleration components of the sensor output. Then, it is shown that the components of the forces in the inertia coordinate system are obtained from the outputs of the low acceleration sensor.

This study aims to examine the mechanism how ball spin rate during baseball pitching is controlled by central nervous system. The participants were seven baseball players. The kinematics and kinetics of the finger, wrist, elbow, and shoulder were calculated using an inverse dynamics method. Kinetic synergies were calculated for joint angles and torques using singular value decomposition. The similarity of spatial pattern of kinetic synergy in each subject was evaluated by cosine similarity. It was indicated that there were three types of synergies: 1) Two pitchers had a synergy that was primarily based on shoulder internal rotation torque, 2) two pitchers had a synergy that was primarily based on elbow extension torque, 3) three pitchers had a synergy that was primarily based on shoulder horizontal adduction torque. In particular, pitchers with a high spin rate relative to ball velocity (SPV) were of the shoulder internal rotation type. On the other hand, pitchers with a low SPV were of the shoulder horizontal adduction type. It is considered that pitchers with a high SPV executed synergy of the shoulder internal rotation torque, which is the same as the direction of ball spin, based on hierarchical control in order to increase ball spin rate. These results suggest that between pitchers with high SPV and low SPV have different spinal nerve activity and motor patterns, respectively.

The purpose of this study was to clarify the relationship between kinematics of the pitching motion and the direction of the spin axis of a pitched baseball. Eight male pitchers were recruited to pitch fastballs. The pitching motion was captured with a three-dimensional motion analysis system. The orientations of whole body segments in a global coordinate system were calculated from the captured data. The directions of spin axis were also calculated on the basis of positional changes of reflective markers that attached to the ball. The spin axis directions were significantly correlated with the upper arm (r=-0.831, p<0.05) and the forearm (r=-0.767, p<0.05) orientations. When a subject whose wrist pronated at the moment of ball release was excluded, the spin axis directions were correlated with the orientations of the hands (r=0.774, p<0.05 / r=0.925, p<0.01) and trunk (r=0.936, p<0.01) as well as the forearms (r= -0.805, p<0.05) and the upper arms (r=0.822, p<0.05 / r=0.763, p<0.05 / r=-0.852, p<0.05). These results suggested that most subjects controlled the spin axis directions with their angular displacement of the upper limb and trunk, but the subject whose wrist pronated at the moment of ball release controlled the spin axis directions with his fingers the only segment that contacts to the ball.

The purpose of this study is to introduce a method for expressing pitching motion as sound (rhythms and melodies). Rhythms and melodies were created from time-series kinematic data for five adult baseball pitchers. We focused on three factors: (1) the attained times and the magnitudes of maximum segmental angular velocities, (2) the movement pattern of pelvic rotation, (3) the movement pattern of the forearm on the pitching side after the foot is raised and used one of the following protocol for sound madding. The protocol 1 presented the times of multiple events as series of notes. A note was assigned to indicate the time and magnitude of each peak so that a rhythm is created to express pitching motion. The protocol 2 presented the movement pattern of a given body segment as pitch (frequency of sound wave). An incorrect technique called “opening up too early” was successfully expressed by transforming pelvic rotation velocity into sound wave frequency..

The word “rise” is used to describe the texture of pitching in baseball. In order to clarify the factors by which the batter perceives “rise” for pitching, we analyzed the parameters such as the physical features of the ball and the tempo of the pitching form in relation to the batter's subjective evaluation. We conducted a Two-alternative forced choice(TAFC) experiment using stimuli that changed the ball speed and the pitching motion time. There were two questions, “Which ball has risen more?” And “Which has the faster ball speed?” In order to achieve both conditional control and a sense of reality, we used a virtual reality baseball system that was originally developed. As a result, it was found that when the tempo of the pitching form is fast, the experiment participants feel that the ball speed is high and the ball is rising. A positive correlation was found between the ball speed and “rise”, but it was confirmed that not only the ball speed but also the pitching form affects the recognition of “rise”.

We have developed a system for easily and comprehensively measuring and evaluating running form characteristics, which uses a single, compact, and lightweight 9-axis inertial sensor attached to the waist. First, in order to establish a group of variables for the purpose, each variable obtained from the sensor was compared with the equivalent one from a high-precision 3D motion capture system (MoCap) and force plate measurement system (FP) for the verification of its validity and reliability. 15 items of spatiotemporal, kinematic and kinetic variables during running were collected synchronously. All the variables except one variable were correlated with the MoCap or FP at a moderate level or higher and also confirmed to be highly reliable. Second, we also conducted a field test with 107 runners of different running levels. It was found that the developed system was able to evaluate running form characteristics appropriately to show difference between athletes’ and recreational runners’ groups in their motion as shown in laboratory tests of previous research. In addition, useful information like time-series changes in the motion of runner in a competitive race was obtained with high sensitivity that had not been achieved before, demonstrating that the system takes advantage of wearable sensor to be available widely without the constraint of measurement condition.

Stroke detection of flatwater canoe sprint single of both kayak and Canadian styles was performed. A portable Real-Time Kinematic (RTK) Global Navigation Satellite System (GNSS) with positioning accuracy of 1 cm, velocity accuracy of 5 cm/sec and sampling rate of 10 Hz was used to measure the movement of canoe and player. Three RTK GNSS receivers were attached per a pair of a canoe and a player. One is on the top of player’s head. The other two were on the stem and the stern of the canoe. Three top-level university canoe players, two of them are kayak style and one is Canadian style, performed a 500 m time trial race on the Onzuiko lake in Japan. A base station for the RTK GNSS was set stationary by the lake. The weather condition was fine with 0-2 m/s headwind. Head movement from start to finish of the race was measured by the RTK GNSS receiver. At the same time, the movement of the stem and the stern of the canoe were also measured, from which the movement of the center of the canoe could be calculated. By calculating the distance vector from the center of the canoe to the player's head, remove the movement of the canoe itself, and only the relative movement of the head with respect to the center of the canoe can be extracted. As the player paddles repeatedly during the race, the movement of the head becomes periodic. From this periodicity of the head movement, the paddling stroke by the player can be detected. Comparison with video analysis showed that 100% stroke detection was possible for canoe sprint single of both kayak and Canadian styles.

The purpose of this study was to investigate the measurement method of drop jump movement by calculating quaternions using a sensor fusion technique based on the Madgwick AHRS algorithm, which is one of the complementary filters. Two healthy adult males were asked to perform a drop jump from a 0.3 m high box with a waist pouch containing an inertial sensor attached to the back of the waist. The test was performed on a force plate and shot using two high-speed cameras that were perfectly synchronized. The Madgwick AHRS algorithm was applied to the acceleration and angular velocity obtained from the inertial sensor, and calculated the acceleration transformed from the sensor coordinate system to the global coordinate system. Linear acceleration was calculated by removing the effect of gravity from the global acceleration, and linear velocity was calculated by time integration and ZVC correction. By using the vertical components of linear acceleration and linear velocity, we were able to obtain data with the same accuracy as the data obtained from digitization and force plates, and we were able to estimate the ground contact time, jump height, and DJ-index to evaluate the drop jump.

Slip-related falls accounts for approximately 25% of falling accidents in work places. Therefore, it is required to know the places in workplace where floor friction is low. Because slip-related falls are likely to occur on icy road surfaces in winter, we aimed to investigate the friction coefficient between a shoe and icy surface using a sensor shoe system in which miniature tri-axial force sensors and inertial measurement units (IMUs) are installed in the outsole. Four tri-axial force sensors were place on the heel, ball, hypothenar, and toe positions, and two IMU were installed on the rear and fore foot parts. An adult male participant was asked to take a step forward with his right foot wearing the sensor shoe system on the icy surface of ice-skating link. The environmental temperature and relative humidity were 2.5℃ and 55%RH, respectively, and temperature of the ice surface was -4.2℃. The step length was 0.6 m or 0. 8 m. The sliding velocity and distance were estimated by integral of acceleration data obtained from IMUs. The friction coefficient at each force sensor position was calculated from the normal and horizontal forces obtained by each force sensor. The results indicated that the peak sliding velocity and sliding distance were not affected by the step length condition. The friction coefficient at the heel and hypothenar was lower than that at the ball and exhibited low values less than 0.1 or 0.05, which was related to large normal force at these locations.