Published papers

This paper describes a procedure for optimizing the design of the landing slope of the Zao jumping hill. The concept behind the design of the landing slope is that the landing slope should enable the spectators to witness an exciting spectacle, that the jumpers can land safely, and that it can be constructed with minimum cost. We regard these features as objective functions. The findings can be summarized as follows: it is possible to control the objective functions by changing the profile of the landing slope; there is not a unique optimal design solution, but the Pareto optimal solutions; a landing slope that gives safety on landing is almost equivalent to a landing slope that produces differences in the flight distance due to differences the jumpers' skill levels; there is a trade-off between the length of the flight distance and safety on landing; the construction cost is influenced by the horizontal distance between the edge of the take-off table and the K-point. The developed procedure would be applicable not only to Zao in Yamagata city, but also to all ski jumping hills in the world.

The purpose of this Study was to develop and validate an automatic procedure using accelerometers and angular rate sensors for detecting exact gait events: heel contact (HC), toe contact (TC), heel off (HO) and toe off (TO). For this purpose, two miniature-sized light sensors were attached to the right shoe which measured triaxial acceleration and biaxial angular velocity of various positions of the shoe while ground reaction force and marker data were recorded at the same time as reference measurements. Healthy men walked on a walkpath at self-selected normal speed with the instrumented shoes on. An automated algorithm was developed to detect HC, TC, HO and TO from the acceleration and angular velocity signals, which were compared with reference data from force plates and markers. The results showed that our method demonstrated similar HC and TO to those with force plates and markers. Moreover, this method well detected stance phase duration. However, TC and HO differed among the three methods (force plates vs. markers vs. sensors). We concluded that the system using inertia sensors can identify TC and HO accurately and be used in gait analysis.

We developed a system for the automatic evaluation of ski jumps on the base of machine learning algorithms. In several capture sessions during summer jump season, motions of four junior ski jumpers were captured by inertial sensors over the complete jump, from the start of the in-run to the end of the outrun phase. Additionally, style points were collected from an experienced judge to serve as ground truth and control data for the machine learning algorithms. All jumps were randomly separated into a training and a test database. Next, we determined kinematic factors such as body segment orientation and body joint position and segmented every jump into its main motion phases on the base of the raw sensor data. Specific motion characteristics that influence the performance and length of a jump were then used to create machine style knowledge from the training database in compliance to the official scoring guidelines. In a last step, we computed the similarity of every jump within the test database to the trained knowledge on a ski jump's style parameters and evaluated the presence or absence of jump errors. Results showed that the computed error annotations conform largely to the human-based judging scores. Adding automatic score measures to the algorithm in future, this method might be an important step towards better measurability and objectivity of performance-oriented sports in form of a mobile competition evaluation system. (C) 2016 The Authors. Published by Elsevier Ltd.

The aim of this study is to clarify the effect of e-health community health promotion program, which consists of both online diet record system and off-line health activities. 49 participants are surveyed concerning self-rated sense of understanding and sense of control about calorie intake, nutrition balance, and physical activity along with basic information, internet usage and lifestyle habit are surveyed during 2009-2001. Self-rated sense of achievement regarding dietary understanding and dietary sense of control significantly increased in a group that utilized the online diet record system. Further analysis shows that the usage of the diet record system affects the self-rated sense of achievement while neither age, sex, answers of the preliminary questionnaire nor session participation had any effect.

'In this study, we investigated the acceleration in punch motion of some martial arts, such as Karate, Boxing, Syorinji Kenpo and non athlete. We predicted the peak impact force of straight punch motion and discriminated the patterns of these martial arts using the time series of their wrist acceleration.In sports trainig, players need feedback of their performance or form in their movement as quickly as possible. Up to now, they usually depended it on motion analysis method by the cine or video films. But it is not practical at the training situation, because it takes a lot of time to get the results of the analysis. On the other hand, the acceleration signal from the playersユ movement is suitable for real time analysis. In martial arts, the impact force of the punch motion is one of the index of playersユ performance. We predicted the impact force by the acceleration time series with high accuracy (r = 0.923 to 0.966 in case of N = 20 about athletes). This method enables us to predict players's performance by only acceleration time series. And each martial arts school, they have a traditional form of their punch motion. We also discriminated these patterns from the acceleration time series.'

This paper describes the hysteresis in the aerodynamic properties of a discus near to its stalling angle. Wind tunnel tests were carried out with a full-size woman's discus. The experimental aerodynamic data D, L and M were obtained from wind tunnel tests as functions of the angle of attack and the spin rate. It was found that the drag, lift and pitching moment coefficients, C-D C-L and C-M, increase with increasing the angle of attack up to a stalling angle of 28-30 degrees. Beyond the stalling angle, C-L and C-M decrease suddenly and abruptly with increasing angle of attack. On the other hand, recovery from the stall does not occur at the same stalling angle of 28-30 degrees when the angle of attack decreases from the stall state; recovery actually occurs at 25 degrees. The C-L-alpha (angle of attack) curve is almost the same when the angle of attack is less than 24 degrees. Therefore, hysteresis occurs near the stalling angle. (C) 2013 The Authors. Published by Elsevier Ltd. Selection and peer-review under responsibility of the School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University

The purpose of this study was validation of a computer simulation on the flight of the flying disc. The flying disc, widely known as the Frisbee (TM), is thrown with rotation for its stable flight. The flight characteristics of the flying disc were identical in comparison with other flying sports materials. The flying disc can keep its lift and glide in the air by the wing effect. However, the traveling direction of the disc was steeply changed in particular conditions. In order to explain this phenomenon, the precise simulation of the disc movement is necessary. In this study, a computer simulation of the flying disc was accomplished. In advance of the simulation, both the three-axial forces and moments acting on the disc were measured in a wind tunnel test for the simulation. For the validation of the simulation results, the authors conducted an experiment using a motion capture system to obtain real flying disc kinematical parameters. (C) 2012 Published by Elsevier Ltd.

To determine the flight path of a discus when it is thrown, it is essential to know what aerodynamic forces are acting on it. However, little data on this is available. Employing a full-size model in a wind tunnel, we have measured the aerodynamic forces acting on a discus spinning on its transverse axis, as well as on a 'non-spinning' discus. The aerodynamic force data (drag, lift and pitching moment) were obtained to create an 'aerodynamic database'. These forces are given as functions over practical ranges of the angle of attack, the spin rate and the wind speed. It was found that the stalling angle was about 30 degrees, and that the lift coefficient increased linearly with increasing angle of attack up to the stalling angle. The estimated lift coefficient obtained by the vortex lattice method agrees with the experimental data within a standard deviation of 0.08. It was observed by oil flow and smoke observation methods that a pair of longitudinal vortexes occur from the 'pressure side' to the 'suction side', similar to wing-tip vortices. These longitudinal vortexes prevent flow-separation up to a high angle of attack, around 30 degrees. The drag coefficient increases with increasing angle of attack up to the stalling angle, and it decreases slightly around the stalling angle, corresponding to a significant and abrupt decrease in lift at the same angle. The coefficient of the pitching moment is almost positive, which is the case with 'nose-up' rotation. There is little difference between the aerodynamic coefficients whether the discus is spinning or not. (C) 2012 Published by Elsevier Ltd.

'Swimmer's propulsive force is maily produced by his arm strokes. Swimmers and coaches are very interested in underwater arm stroke motion. However, so far, in order to examine stroke motion, we had to prepare underwater cameras for the kinematical observation. Although we could prepare those facilities, it was very difficult for us to detect which stroke phase would be improved, or which underwater phase would be changed by their fatigue. The authors reported that the swimmer's wrist acceleration has several characteristics of their swimming styles. Some are common between subjects and the others are swimmer's own characteristics. In addition, swimmer's skill level is appeared their wrist acceleration. The authors developed microcomputer-based data logging device for swimming research. This newly developed device make us observe tri-axial swimmer's wrist acceleration in swimming over an hour with non-restricted. We applied it for the evaluation of swimming stroke motion. Especially, in this study, we focused on the change of the wrist acceleration by swimmer's fatigue during intensive interval training. We took three dimensional motion analysis for the kinematical quantitative evaluation and blood lactate test as a physical quantitative evaluation of the swimmer's fatigue. As a result, swimmers' stroke motion had changed under their exhaustion. And those change were also observed in acceleration patterns.'

'In the field of experiment or data analysis, we need both a good data storage tool and a computational tool. A combination of databases and Mathematica will be an ideal solution for such situation. In order to satisfy this need, we built a mathlink program, 'Mathgres' which connects PostgreSQL with Mathematica. 'Mathgres' makes us store Mathematica data into PostgreSQL and retrieve it to Mathematica. As the result of this environment, we found; (1) Instead of scattering the data files in saving, database can integrate the data and makes the process of data analysis smooth. (2) We can easily maintain both the experimental data and its related information together. This is very useful tool in the sports biomechanics field.'

We measured aerodynamic forces acting on real jumping flights in the take-off phase as well as a quasi-steady flight phase. The frame rate was 250 frames/s. It is concluded that the present aerodynamic force data derived from the image analysis are found to be in fair agreement with existing wind tunnel data for the cases of jumping flights in the quasi-steady flight phase. The aerodynamic data in the cases of relatively large forward leaning angle, which is typical in the initial phase of a jumping, could also be obtained. The lift in the take-off phase is relatively larger when compared with the quasi-steady flight phase.

The purpose of this research is to estimate the velocity, angular velocity and direction of the rotational axis of the flying ball by the accelerometer. A subject performed pitching by using the sensor ball. And, the closed up release point image was acquired using the high speed cameras. The distance from the release point to the switch is measured image analysis and the velocity of each trial was estimated by the flight time of the ball. The angular velocity was estimated from the gravitational and the translational acceleration. The direction of the rotational axis was estimated from the component of the centrifugal acceleration. Each estimated value was compared to the value calculated by the high speed cameras. The velocity difference between the estimation value and the calculation value was about 1.85 (m/s). The difference of the angular velocity was about 0.57 (rad). The difference of the rotational axis was about 0.41 (rad). And it was observed that the rotational axis on the sensor coordinate system changed during flight phase.