Closed Change and Whisk which have common and different features each other are analysed in mechanical point of view. The movement of Whisk in Waltz representing the transition from the closed position to the promenade position in ballroom dancing is described by a method proposed in the present paper. The position and movement of dancers are composed of the movement of couple centre, the rotation of the couple as a solid and the rotation of each dancer around each dancer’s centre. Three types of Whisk are examined and compared. The kinetic and potential energies in each case are analysed and discussed. Choosing an adequate type in Whisk in actual dancing occasions is suggested.

Viennese Waltz Dance in international style is analysed in the mechanical point of view. The movement of dancers is compared with that of English Waltz. Difference between Natural Turn and Reverse Turn is cleared. The exchange in the kinetic energy between translational movement and the rotational movement is dominant in the Viennese Waltz whereas the exchange between the potential energy and the kinetic energy is more essential in the English Waltz. Rise and Fall and the sway are analysed. Natural Turn, Reverse Turn and Change Steps are studied showing the trajectories of each dancer together with kinetic energies and mutual force between partners to match mechanically smooth movement.

In Japan, it is estimated that there are about 12.8 million people who have osteoporosis, and it is expected that the number of osteoporosis patients may continue to increase. DXA is used to measure bone strength, however bone strength using DXA may not be measured accurately, and it is difficult to measure it in terms of safety and ease. In this study, we have performed machine learnings to predict bone strength obtained by the hammering test of bones. To predict bone strength, age, body composition, and physical fitness test data were used as explanatory variables. The accuracy of models using linear regression, decision tree and neural network were compared. It was found that the model using a decision tree showed the highest accuracy. It was confirmed that the same prediction values were obtained in the case of the decision tree model, though the measurement values were different. Further modeling is still necessary to optimize the accuracy of the predictions.

Beginners in table tennis often rely on their wrists rather than their elbows when executing backhand strokes. Since both wrist and elbow movements contribute to hand control, it is anticipated that restricting wrist movement will encourage greater use of the elbow. In this study, we developed a wearable device designed to restrict wrist movement as a training tool to promote elbow-utilized swings. To ensure that the device does not interfere with other movements, it was designed to be lightweight and to engage its restraining effect only during rapid wrist movements, utilizing an air damper mechanism. We conducted a comparative experiment involving trials with and without the device to assess its effectiveness in enhancing elbow use following training. The findings indicated that training with the device led to a significant restriction of wrist movement and a corresponding increase in elbow use, suggesting that the device effectively encouraged the desired motor adaptation.

Fatigue-induced performance reductions in jump, landing balance, and the agility of directional changes after landing can lead to decreased sports performance and an increased risk of injury. While pelvic belts are employed to enhance jumping and landing performance, their efficacy in reducing post-fatigue performance declines remains unclear. The purpose of this study was to investigate whether a compression garment with a pelvic belt (CG-PB) can suppress the deterioration of jumping and landing performance after fatigue. We hypothesized that wearing the CG-PB would contribute to reducing performance declines following fatigue. The experiment involved ten male participants and was conducted under two conditions: with and without the CG-PB (BELT and CON). Before and after the fatigue-inducing tasks, participants performed counter movement jumps (CMJ), single leg landings, and landing cuttings (LC), during which their movements and ground reaction forces were measured. While significant decreases in jump height during CMJ and lateral propulsion force during LC were observed post-fatigue in the CON (CMJ: p = 0.01, LC: p = 0.04), no significant differences were observed in the BELT before and after fatigue (CMJ: p = 0.99, LC: p = 0.13). Thus, the CGPB potentially relieves the reduction in vertical jump height and lateral propulsion force during LC after fatigue.

The Center for Winter Sports Science and Research at the Kitami Institute of Technology provides technical assistance to Alpine skiers and adjusts ski boots from an engineering perspective. Experimental verifications have revealed that the downhill speed in Alpine skiing is related to the angle of inward lean (angle at the turn), and that the angle of inward lean is affected by the angle of inward lean (angle formed by the footbed of the boot). In this study, we conducted skiing experiments using the ski simulator “SkyTech” to evaluate the effects of the angle of inward lean and the cross-sectional shape of the attached parts on the angle of inward lean and the turn speed, and examined the appropriate parts for ski boots.

The McKibben-type rubber actuator, which contracts when pneumatic pressure is applied, features the ability to deliver a wide dynamic range of force through pneumatic control while maintaining flexibility. This characteristic suggests a high compatibility with fitness equipment, prompting us to conduct prototype evaluations to verify this potential. As examples, we prototyped and tested an arm curl upper limb training device, a bench press upper body training device, and a lower limb stretching device, confirming their utility. These results indicate that rubber actuators have a high suitability for assisting human motion.

Anterior cruciate ligament (ACL) injuries are among the most common ligament injuries, with one contributing factor being excessive knee valgus angles during the landing motion after jumps. In this research, the authors have worked on an approach to constrain knee valgus motion by applying mechanical stimuli to the lower limb. As an approach of applying stimuli, we focused on the tension transmission pathway through myofascial and the mechanoreceptors in the toes, which contribute to the body motion coordination. Based on this pathway, we placed a wire along the surface of the lower limb and developed two mechanisms to constrain knee valgus motion using wire tension. The first one is a tensioning mechanism that allows for adjustable wire tension, enabling investigation of movement conditions that influence valgus motion during landings. Second one is braking mechanism that incorporates a mechanism to brake the wire only during landing in knee valgus motion, for use in practical situations. The knee valgus angle measured in the jumping experiments indicated that each device could affect constraining valgus motion.

In an outside pass in soccer, we observe four strategies: the backswing, the stopping of the leg, the guiding of the foot outward as the knee joint extends, and the stopping of the follow-through. The aim of this research is to validate if we observe these four strategies by training the agent with a reward focused on kicking a faster ball. Additionally, we aim to investigate the contribution of the collateral ligaments in the outside pass. We built two leg models: (a) a two-degree-of-freedom leg model that can apply roll torque around the hip joint, and (b) a three-degree-of-freedom leg model that can apply pitch-roll-yaw torque around the hip joint and pitch torque around the knee joint. We trained a Deep Deterministic Policy Gradient (DDPG) agent using these two leg models and analyzed the torque around the hip and knee joints, as well as the ball velocity after the leg loses contact with the ball. In the (a) two-degree-of-freedom leg model, the agent shows the stopping the follow-through strategy at the episode 1826, and it shows both the backswing strategy and stopping the follow-through strategies at episode 3000. In the (b) three-degree-of-freedom leg model, the agent shows the guiding of the foot outward as the knee joint extends and the stopping follow-through at episode 2127, and the same strategies were observed at episode 3000. Leg model (a), which utilizes the collateral ligaments’ stiffness resulted in a faster ball compared to leg model (b), which is capable of moving in directions that do not engage the collateral ligaments’ stiffness. This suggests that utilizing collateral ligaments’ stiffness has advantage for kicking faster balls in an outside pass. This findings will lead to finding new collateral ligaments’ functions.

Golf is not only a sport to compete for scores, but also to enjoy the comfort of a good shot. In order to hit a good shot, it is important to use a golf club that is appropriate for the golf swing. Therefore, various previous studies on the golf swing have been conducted. It is also necessary to find commonalities among golfers in order to improve the golf swing. The authors extracted common features of angular velocity and acceleration waveforms during golf swing motion in participants who showed common features of shaft deformation behavior in a previous study. The purpose of this study is to extract common points of golf swing motion using torque data exerted during the golf swing motion. First, the golf swing motion was measured, and the torque data exerted during the golf swing motion was calculated. Next, singular value decomposition was performed on the observation matrix consisting of the torque data of all participants to determine the number of modes to represent the torque data. A cluster analysis was performed using the right singular vector for the determined modes, and the participants were classified into a small number of groups. Finally, by comparing the swinging motion between the groups, we found that the swing planes were different.

In curling, the evaluation of the ice sheet condition determines the accuracy of shots and affects victory or defeat. However, its evaluation depends on individual sensory perception and there is no clear index. It is also difficult to measure the ice sheet condition because it varies depending on multiple factors such as temperature, humidity, and air flow in the curling hall. In this study, we develop the numerical approach to evaluate the ice sheet condition with the aim of unifying the senses within a team and leading to a decision for reliable strategy to enhance team performance. In this paper, we conducted CFD using temperature, wind speed, and other data measured at an actual curling hall to grasp the overall condition of the curling hall. The results were compared with the actual measured values, and it showed a similar trend. We also evaluated the ice sheet condition using the condensation rate giving from CFD results.

In baseball and softball, sting occurs in the batter’s hand when the batter hits off-center of the bat. In this study, we hypothesized that multiple vibrations have a composite effect on the sting experienced when hitting off-center of the bat, and that the influence of each mode varies depending on the grip position. We conducted a quantitative investigation of the relationship between sting and vibration when a ball was actually collided with a bat. The investigation was divided into two experiments. First, we measured the vibration in the grip when a ball was collided with a bat hung by a string. Second, we conducted a sensory evaluation of the strength of the sting when a subject simulated hitting a ball with a bat, and the ball was collided with the bat. From the results of the vibration measurements and the sensory evaluation, we considered that multiple vibration modes are related to the sting caused when hitting off-center of the bat. Based on this, we designed a lattice-style dynamic vibration absorber for bats that simultaneously reduces multiple vibration modes that cause sting.

One of the most prominent features distinguishing skill levels of expert and amateur golfers is efficiency of swing movements. During the downswing, the release of wrist cock occurs as a result of bottom-up increase in segmental velocities, which is supposed to contribute to the efficient club head acceleration before the impact. Such dynamic properties are, however, hard to visually understand. In this paper, we evaluated the relationship between dynamic release characteristics and performance outcomes in a group of professional and amateur golfers, using an IMU-based swing analysis system (M-Tracer) and a radar-based ball tracking system (Trackman). Specifically, we measured (1) the elapsed time from the onset of release to the impact, (2) the angle between the direction of grip velocity and club shaft at the release onset, and (3) the carry distance of the ball. In all of the three measures, the professionals generally showed larger values with smaller variances than the amateurs. Based on these considerations, we developed a smartphone application to facilitate self-learning of efficient swing skills. Our application wirelessly collects data from the M-Tracer and a pair of pressure-sensing insoles (OpenGo) and provides an integrated feedback immediately after each shot. The appearance includes information regarding the release-related dynamic properties and the spatio-temporal foot contact patterns, enabling users to intuitively grasp how their swing can be more efficient.

There are many sports in which throwing motion is used, such as baseball and shot put, but the throwing form differs depending on the individual and the competition. Factors that cause throwing forms to vary among individuals and competitions include differences due to parameters such as the weight of the thrown objects, body inertia, and body size. Although there has been research on throwing motion in specific competitions, no general theory has been established regarding the strategies under which various throwing forms are based. In this research, we examine, consider, and discuss the strategies of throwing form for the baseball and the shot put. Using reinforcement learning, we derived throwing forms for high-speed throwing according to parameters. The relationship between parameters and throwing forms was then compared and analyzed. As a result of comparing the optimally differentiated throwing forms for each parameter, the throwing form strategy due to differences in the weight of thrown objects may differ in terms of the angle of the upper arm at release and the angular acceleration of the shoulder and elbow, and the strategy due to the degree of push of the arm and the influence of the forearm and upper arm. Throwing form strategy due to differences in body size may also include differences in strategy due to the influence of the amount of torque applied to rotate the arm depending on the length of the moment arm and the speed at which the forearm and upper arm are rotated, in terms of the timing of elbow advancement and the angular acceleration of the shoulder and elbow.

In this study, we aim to classify golf balls of different surface specifications using machine learning. We analyze trajectory data obtained from ITR (Indoor Test Range), in which three types of golf balls (C, D, and G) with the different specifications are used. Two balls (C and D) exhibit similar aerodynamic properties, while the third (G) shows rather different characteristics. When the original trajectory data are used as features, the classification accuracy is approximately 60%. Then, we employ the coefficients of the third-order interpolation of the trajectories as features. This results in the accuracy of over 80% for distinguishing between balls C/G and D/G. However, for the balls C and D with similar characteristics, the accuracy remains low, likely due to multicollinearity caused by correlations among the features.

To enhance the classification of balls with similar properties, we apply L1 regularization for dimensionality reduction. Our results show that a model using only three features—spin rate at launching, horizontal and vertical accelerations— can accurately classify the balls C/G and D/G. On the other hand, further improvements are needed to enhance classification accuracy for balls with similar characteristics.

In this research, we aim to develop a system that specializes in "supporting players' condition, mental training," and so on. Specifically, we will develop an "AI coaching system" that uses AI to analyze sports conditions and provide coaching. In order to understand what the trends are on average; we asked several people to respond to the Kyushu Information University Track and Field Club in a ``medical questionnaire'' and analyzed the data to understand the trends among university students. In the end, we will think about what kind of "AI coaching" design we will create. In the future, we will design an "AI coaching" system that understands trends, and use it to plan future tournaments. It is used for conditioning.

Chronic traumatic encephalopathy (CTE) has become a concern in soccer. A possible mechanism of CTE is related to pressure waves which propagate on the brain and shear deformation caused by rotational head motion. To evaluate the brain deformation behavior during head impact, a novel headform which can measure the brain acceleration and angular velocity has been developed. In this study, we compared the results of the ball heading tests using the headform and their reconstruction simulation using a finite element model of a human to investigate whether the linear acceleration waveforms at the brain sensors of the headform capture the characteristics of the pressure waveforms. The characteristics of linear acceleration waveforms measured by the headform were generally consistent with the linear acceleration waveforms obtained by simulations. Also, comparison of the linear acceleration and pressure waveforms showed that the linear acceleration waveforms capture the characteristics of the pressure waveforms for each impact condition.

High school baseball players across the country are practicing hard every day with the goal of playing at Koshien. In recent years, data analysis has become the key to determining the outcome of games. So we developed this system to contribute to Koshien participation and to increasing the number of baseball players. This time, we conducted a simple regression analysis to examine the correlation between batting average and strikeout rate. A simple regression analysis revealed that the contribution rate was 8%, indicating no correlation between the two.

In this study, pitching experiments were conducted with two pitchers (pitcher A and pitcher B) under different friction conditions between the fingertips and the ball to investigate the effects of friction conditions between the fingertips and the ball on pitching performance, upper limb motion, and forearm muscle activity during pitching. The results showed that, for pitcher A, the ball speed and ball spin rate decreased and the pitch control of the ball decreased under the water-applied condition compared to the rosin powder-applied condition. In the water-applied condition, pitcher A performed upper limb movements to reduce his hand velocity and increase the pitching radius, which resulted in the reduced centrifugal force in the acceleration period. Furthermore, the muscle synergy patterns changed between the water- and rosin powder-applied conditions in pitcher A. In pitcher B, the ball spin rate decreased in the water-applied condition compared to the rosin powder-applied condition, but there was no change in pitch velocity and pitch control. The centrifugal force exerted on the hand during the acceleration phase did not change under the water-applied condition compared to the rosin powder-applied condition, and there was no effect on the muscle synergy patterns in pitcher B. However, the muscle activity of the shallow finger flexors and ulnar carpal extensors increased in the water-applied condition, suggesting that the pitcher B were trying to suppress slippage by increasing their grip on the ball.

In recent years, pitchers have faced increased risks of being hit by pitches due to advancements in bat performance and the physical capabilities of baseball players. This has led to serious accidents, including concussions and skull fractures, from being struck in the head. To enhance pitcher safety, head guards are essential. Unlike helmets, head guards are lightweight and specifically designed to protect the sides of the head. In this study, two types of prototypes were developed to protect the sides of the head: a pitcher’s head guard cut from a batter’s helmet and a pitcher’s head guard created by removing the right side of a pitcher’s existing headgear. Their effectiveness was evaluated through collision experiments using a baseball and a human head model. The evaluation focused on two key factors: impacts that could cause skull fractures and those that could lead to concussions. Acceleration and impact load measurements were used to estimate potential brain and skull damage, respectively. The results demonstrated that the pitcher’s headgear provided the best protection against both concussions and skull fractures.

The purpose of this study is to clarify the relationship between the surface shape and aerodynamic characteristics of knitted fabrics used in sports garment fabrics. In particular, the study examined how the combination of macro roughness (e.g. grooves and dimples) and micro roughness (coarseness due to the weave) affects fluid phenomena. Using wind tunnel experiments and particle image velocimetry (PIV), the drag characteristics and flow in the wake region of five different types of knitted fabric were analyzed. As a result, drag crises were observed in three types of fabric: Dimple, Simple + Rib, and Groove. In particular, the drag area SD was minimized at U = 10 m/s for Dimple, U = 12 m/s for Simple + Rib, and U = 14 m/s for Groove. On the other hand, no significant changes were observed in the fabrics of Simple and Rib. In the PIV measurements, the wind speed U at which the minimum SD and the minimum width of the low-speed range were observed were the same for Dimple, but they were different for Simple + Rib and Groove. The results of this study are expected to contribute to the selection and design of fabrics that consider the interaction between macro and micro roughness in the development of sports garment fabrics.

In this study, a walking motion analysis method was developed by a shoe equipped with an embedded ultrasmall multi-axis tactile sensor. The shoe made it possible to measure the three-dimensional forces acting on the foot anywhere while walking. This study aimed to explore the application of a shoe with embedded sensors for micro-level 3-dimensional forces motion evaluation. We conducted two experiments. First, we focused on small areas of the sole where the sensors were embedded and measured the loads applied to the foot using tactile sensors. As a result, we confirmed that embedding sensors with an elastomer facing the sole enables the measurement of 3-dimensional forces acting on the foot. Additionally, we investigated the potential for motion analysis by attaching sensor-embedded shoes to a simulated foot and verified the capability to measure the forces acting on the foot.

Numerical simulation was performed for the flows past an archery bare-shaft arrow at small attack angles. The Reynolds number Re based on the shaft diameter was varied between 1.0 x 10⁴ and 2.0 x 10⁴, and the attack angle was varied from 0 degrees to 1.4 degrees. Computations were carried out for bare-shaft arrows with two different kinds of arrow point, i.e. streamlined point and bulge point. The behavior of the boundary layer along the arrow shaft was extensively studied by means of post process visualization. According to the excerpt extracted from the results of parametric study, it was confirmed that the boundary layer flow maintains steady state for a part of the parameter plane studied. Furthermore, it was remarked that, for the arrow with bulge point at high Re, unsteady motion was triggered by separation bubble in the vicinity of arrow point, while at low Re, unsteady motion was initiated by the emergence of low-speed wave-like structure near the arrow tail on the back side of the shaft.

We use Bayesian linear regression to estimate aerodynamic coefficients from trajectory data containing measurement noise and error. The third polynomial is employed to interpolate two-dimensional trajectory data of a non-rotating table tennis ball. Each term in the polynomial is obtained as a posterior distribution. From the third polynomial, we investigate the time variations of the drag and lift coefficients. In Bayesian linear regression, the distributions of the coefficients of the polynomial including the optimal solution are obtained. It is found that two hyperparameters have significant impact on the estimation of the posterior distribution: the variance of the prior distribution in Bayes' theorem and that of observation which indicates the extent of error in linear regression. We set the prior variance for each term of the polynomial and estimate the coefficients. By normalizing the data, we can produce a more accurate polynomial. Compared to the polynomial without the normalization, there are distinct differences in the distributions for the third and constant terms. This shows that these two coefficients have large impact on the formation of the polynomial. Furthermore, based on the relationships between the estimated terms, it is found that the constant and first terms have the strongest negative correlation. In addition, by expressing the aerodynamic coefficients as probability distributions, it become possible to interpret stochastically the measurement errors.

The purpose of this study is to verify the discrimination ability of the portable two-dimensional impact tester in identifying the shock attenuation properties of various sports surfaces. In our previous studies, we developed a portable two-dimensional impact tester to investigate the properties of installed fields, especially for horizontal shock attenuation to prevent injuries in sports activities involving artificial turf.In this study, three different hardness levels of artificial turf were installed on acrylic cases. The soft sample consists of rubber and sand in a 6:4 mix, the normal sample has a 5:5 ratio, and the hard sample has a 4:6 ratio. A 60 kg impact weight was dropped from a height of 55 mm onto the center of the impact sensor unit, using eight initial impact angles ranging from 0 degrees to 35 degrees in 5-degree increments. Horizontal and vertical impact forces, as well as horizontal and vertical displacements and angles of the parallelogram linkage, were recorded.Although the vertical maximum forces of the three specimens at various initial impact angles were almost the same, the horizontal maximum forces of the soft specimen were noticeably greater than those of the normal and hard specimens across the various angles. As a result, the impact sensor unit can be transferred after impac t very easily in the soft specimen because the rubber infill does not effectively suppress the movement of the sensor unit. Finally, data from the portable two-dimensional impact tester can be used to identify the properties of the specimens.

Differences in foot kinetics related to foot alignment have been suggested to be a contributing factor for running-related injuries. However, the influence of foot alignment on multi-segmental foot kinetics during running remains incompletely understood. The present study aimed to investigate the relationship between foot alignment and inter-segmental foot kinetics during running. Twelve males performed barefoot running with rearfoot strike at 3.3 m/s ± 10% along a 10 m runway. We simultaneously recorded multi-segmental foot kinematics, plantar pressure, and ground reaction force using a three-dimensional motion analysis system and a plantar pressure sensor. The ground reaction force was distributed to the rear- and forefoot based on the pressure ratio of each segment. Sagittal moment, power and work at the ankle and midfoot were calculated using an inverse dynamics approach. Foot alignment was assessed by Foot Posture Index (FPI). Spearman's rank correlation coefficient was used to examine the relationship between FPI and kinetic parameters at the ankle and midfoot (α = 0.05). FPI was significantly correlated with peak plantarflexion moment at the ankle and midfoot (ρ = 0.72, p < 0.01; ρ = 0.63, p = 0.03, respectively). FPI also showed a significant correlation with peak positive power (ρ = −0.70, p = 0.01) and positive/negative work at the ankle (ρ = −0.71, p < 0.01; p = 0.63, p = 0.03, respectively). These findings suggest that the assessment of foot alignment is useful for estimating the foot and ankle kinetics during running.

This study aimed to examine the effects of using a sticky substance on baseball pitching performance, specifically when applied as part of a training regimen. Seven male pitchers participated, and the Rapsodo Pitching 2.0 system was used to measure performance metrics. The experiment involved two groups: a Control group and a Training group, with trials conducted across three phases: Pre, Training, and Post. In the Pre and Post phases, participants pitched 5 times, while in the Training phase, they pitched 10 times toward a target 18.44 m away. Valid pitches were recorded by Rapsodo Pitching 2.0. Each participant completed the trials over two consecutive days. Ball velocity, spin rate, gyro degree, and vertical break were measured, and a t-test was conducted. Results showed no significant differences between the Control and Training groups in the Post phase. However, during the Training phase, the Training group exhibited significantly higher ball spin and vertical break (p < 0.05), likely due to increased friction between the fingers and the ball. Interestingly, some participants did not achieve a significant increase in ball spin, despite the sticky substance's known effect. This variability suggests a need to investigate the factors influencing ball spin to develop more effective training methods.

This study created a simulated body system consisting of a simple 3D-printed knee joint model equipped with high-sensitivity three-component force sensors. Several types of sportswear made from different materials were worn on the simulated body, and the forces exerted on the system during movement were measured. The aim of this study was to clarify the relationship between the material properties and the forces acting on the simulated body from the sportswear. The results showed that (1) the friction coefficient of the material affects the longitudinal component of the force exerted on the simulated body, (2) Young's modulus along the longitudinal direction of the simulated body affects the longitudinal and radial components of the force, and (3) Young's modulus along the tangential direction of the simulated body affects the longitudinal and radial components of the force only in areas with longitudinal curvature.

The enlargement of racket faces and the reduction in racket weight have made topspin techniques more common, drawing increased attention to racket types and their performance. However, this trend has also revealed the limitations of further weight reduction. To address these challenges, new rackets featuring innovative designs aimed at overcoming the constraints of lightness were introduced to the market. While many of these rackets emphasized high performance, they have since disappeared from shelves. This study examined racket performance by analyzing the experimentally identified physical properties of various racket models and conducting collision simulations. The findings indicate that racket weight and weight distribution are the most critical design factors.

A 54-tooth CFRP chain sprocket for bicycles was molded using short 3K carbon fiber bundles impregnated with epoxy resin under a pressure of several kPa in a silicone rubber mold, with the carbon fibers oriented in a mountain shape toward the tooth tips. The weight is 50% lighter than the 7075 super duralumin chain sprocket. The developed CFRP chain sprocket was used to travel 3,500 km over a four-year period. Compared to the 7075 super duralumin chain sprocket, the CFRP chain sprocket required approximately 10% less watts when traveling at 20 km/h on flat ground, and approximately 25% less watts when climbing a 10% gradient. Experimental analysis showed that the CFRP tooth tips deform in the tooth width direction due to the chain tension, which makes it easier to climb hills by releasing the stress accumulated at the bottom dead center of the crank. All 54 teeth of the CFRP chain sprocket were worn, with 26% of the tooth tips chipped and 27% of the tooth tips having holes with a diameter of 0.3 to 0.5 mm. In addition, 22% of the tooth bases were chipped and 15% of the tooth bases had chips. There were holes. The tooth wear was greatest at ±45° to the crank axis. The CFRP chain sprocket also had low lateral rigidity, about 1/5 that of a 7075 super duralumin chain sprocket, and when shifting gears at the front, the chain sprocket deformed and the chain could not move, requiring three and a half turns to change gears. For comparison, a front single chain sprocket with 56 teeth machined from a CFRP plate was 280% heavier than a silicone rubber molded CFRP chain sprocket. A 1000km running test was conducted over a four-year period. All teeth were worn, but no chips or holes were observed. A repair technique was developed to reinforce the tooth base of a worn CFRP chain sprocket using a commercially available chain as a mold, with 3K carbon fiber bundles and epoxy adhesive.

In this study, a whole-body motion control simulator, originally developed for humanoid robots, was applied to the analysis of human motion. A simulation of whole-body motion of a human model was implemented, focusing on rotational jumping motions around the horizontal and sagittal axes. The validity of the simulation was confirmed by comparing the motion data with human motion measurement data from prior studies in the fields of ergonomics and sports science. The comparison involved isometric joint torque measured using the make test method from previous studies and vertical ground reaction forces in the z-axis direction obtained from force plates. As the simulation results were of the same order of magnitude as these data, the results were deemed accurate. This simulation serves as a valuable tool for the quantitative evaluation of human motion during rotational jumping motions.

Dynamic balance from straight arm press to handstand with legs together in gymnastics is investigated by constructing a motor control model and measuring the movement. Simulation results showed that the handstand movement where the center of mass is lifted strictly along the vertical axis can be achieved by slightly shifting the center of pressure back and forth while maintaining the floor reaction force in the vertical direction. Based on the simulation and measurement results, the static and dynamic components of the torque around the wrist joint and the torque around the center of mass were confirmed.

In hurdle races, in order to reduce the running time, it is necessary to maintain a high running speed and to have good hurdling technique that allows for small deceleration. In addition to this, in the long sprint hurdles, athletes are also required to run between the hurdles in as few steps as possible, and to do so in an even number of steps. The technique to fulfill this is to jump over by stepping off with your non-dominant leg. Most research on this technology has focused on lace patterns, and there are few studies that have focused on movement. The subjects of research focusing on movement are top athletes, and it is difficult to apply it to beginners, who are thought to place more importance on techniques for taking off with their non-dominant foot. In this study, we compared the hurdle-jumping movements of 21 beginners, focusing on the leg that jumps over the hurdle when the dominant and non-dominant legs are used. The hurdle height was set at either low or middle. As a result, there was no difference between the dominant and non-dominant legs in the low hurdle condition. On the other hand, in the middle hurdle condition, the maximum hip abduction angle of the non-dominant leg was smaller than that of the dominant leg. In learning to jump over hurdles with the non-dominant leg for beginners, it was suggested that focusing on the abduction of the trail leg and the rotation of the corresponding body part in the middle hurdles would be effective.