Published papers

The purpose of this study was to develop a microcomputer-based acceleration logger device for the swimming stroke monitoring. The authors measured the swimmer's tri-axial wrist acceleration and applied this device for the fatigue evaluation of the swimmers. The experimental protocol led the swimmers exhausted after the crawl stroke interval training. Every single stroke was determined by the impact acceleration peak, which appeared on the x and z-axis acceleration. The change of the underwater stroke phases was identified by the characteristics of the acceleration peaks. In their exhaustion, the y-axis acceleration, which was longitudinal forearm acceleration decreased at the beginning of the upsweep phase. At that time, the swimmer could not extend his elbow joint. Since the developed acceleration data logger could provide us the information about the underwater stroke phases and it would be a helpful tool in the swimming training.

A stochastic model of swimming speed over the course of a male 200 m freestyle swimming race is proposed. It builds on a dynamical model reflecting the trade-off between drag and propulsion in swimming. The parameters of the model are estimated from elapsed time data observed at several points along the pool. The model fits the data well and also provides a good description of the swimming strategies of each swimmer from phase to phase in the race. An individual factor measuring how much faster or slower the individual swims relative to the average swimming speed of the race is simultaneously estimated in the course of fitting the model. This factor is, as expected, closely related to the final outcome of the race. (c) 2007 Elsevier Ltd. All rights reserved.

This paper describes the concurrent optimization of the design of a discus and the skill with which it is thrown. The objective function for optimization is the flight distance, where longer is better. Thirteen control variables are considered, twelve of which are concerned with the skill of the thrower. These determine the launch conditions, which are controlled by the thrower when he or she throws the discus. The final variable is concerned with the discus itself. This is the moment of inertia on its transverse axis. The optimization was carried out with the aid of a genetic algorithm, and the entire trend for each generation between the objective function and the control variables could be visualized with the aid of self organizing maps. It was found that the flight distance achieved with concurrent optimization was longer than that optimized for skill alone. In the case of the optimal flight, the angle of attack should always be less than the stalling angle. (C) 2012 Published by Elsevier Ltd.

'We observed swimmers' right forearm acceleration in swimming using the tri-axes strain gaged accelerometer. The results of the experiment shows that there were some characteristics about each stroke style and subjectユs own stroke pattern in accelerations. It was suggested that there were possibilities to analyze each phase of the swimming stroke from the acceleration signal directly. We normalized each stroke cycle duration into [0, 1]. Acceleration values were extracted from X, Y, Z axes at the same interval with respect to normalized time. We discriminated whether a certain one cycle acceleration pattern had belonged to which stroke style, such as freestyle or breast stroke. In this study, we applied the Maharanobisユs generalized distance to our study which is a one of the method of the discriminant analysis. We discriminated a certain acceleration series in case of N = 10, 20, 25. The results of this discrimination indicated that there were possibility that we could discriminate a certain one stroke cycle belongs to which stroke styles in high accuracy using acceleration signals(Error Discriminant Ratio = 1.96[%]).'

A study was undertaken to investigate the influence of shaft stiffness on the deflection and the positioning of the club face during a golf swing. To accomplish this task, a theoretical model was developed that calculated deflections of golf shafts during the swing. Applying moment-curvature in relation to a shaft that had the bending stiffness, a differential equation and the boundary conditions that characterized its behaviour over the duration of the swing were generated. Incorporated into the bending moment-distribution are forces and torques acting at each end of the shaft. These loads were calculated using an inverse dynamics problem of the golf club during the swing. A motion capture system was utilized to collect the necessary data. Solutions to the equations of motion for the shaft were calculated numerically. The results have been presented as deflections along the shaft as functions of time. Bending deflections were determined in the plane of the club face and normal to this plane were calculated. (C) 2014 Elsevier Ltd.

The objective of this study was to develop a swimming motion display system for athlete swimmers' training, which is handier and more intuitive than the three dimensional motion capture systems using underwater cameras. In this paper, system structure, reconstruction method of the swimming motion, experiment on land to examine the accuracy, and the software which reconstructs and displays the swimming motion are described. (C) 2010 Published by Elsevier Ltd.

Ten participants were assessed while walking in water and on land with wearable inertial measurement units (IMUs) attached to the right thigh. Longitudinal acceleration, anterior-posterior acceleration, and frontal axis angular velocity were measured at 100 Hz, matched with video analysis sampled at 25 Hz during the walking trials. The longitudinal acceleration showed almost 1 g from initial heel contact to 70% of one cycle, and the anterior-posterior acceleration showed a sinusoidal pattern, synchronizing the approximate posture of the thigh in water. The frontal axis angular velocity fluctuated less while walking in water compared with on land, because thigh motion speed was slower in water than on land. The acceleration and angular velocity in water were stable and did not fluctuate. Walking exercises in water may be effective in individuals with knee- or thigh-related medical issues.

Aerodynamic forces, drag and lift were estimated by the body attached inertia sensors and high speed videography in ski jumping. Last ISEA conference, the authors presented our new method for the aerodynamic study on ski Jumping. In this paper, we propose more robust and reliable measurement system by using wireless technology. Wireless 6DOF inertia sensor platform, which has a built-in tri-axial accelerometer and three single axial gyroscopes, was attached on the jumper's low back. The authors adopted IEEE802.15.4 for the start trigger and real time monitoring during long training session. Sensor also has a flush memory inside for one hour data storage at 250Hz. The primary target of the present study is to extract the aerodynamic force data during real jumping flight. Angular velocity on the sagittal plane was directly measured from the gyroscope. Then we could obtain the jumper's body pitch angle by its time integration. The accelerations with respect to the body local coordinate system which was determined by the body pitch angle, indicated the drag and lift forces. The assessment of the aerodynamic forces of ski jumping was examined by both of the sensor data and the kinematical data in this study.

Aerodynamic forces, drag and lift were estimated by the body attached inertia sensors and high speed videography in ski jumping. Last ISEA conference, the authors presented our new method for the aerodynamic study on ski Jumping. In this paper, we propose more robust and reliable measurement system by using wireless technology. Wireless 6DOF inertia sensor platform, which has a built-in tri-axial accelerometer and three single axial gyroscopes, was attached on the jumper's low back. The authors adopted IEEE802.15.4 for the start trigger and real time monitoring during long training session. Sensor also has a flush memory inside for one hour data storage at 250Hz. The primary target of the present study is to extract the aerodynamic force data during real jumping flight. Angular velocity on the sagittal plane was directly measured from the gyroscope. Then we could obtain the jumper's body pitch angle by its time integration. The accelerations with respect to the body local coordinate system which was determined by the body pitch angle, indicated the drag and lift forces. The assessment of the aerodynamic forces of ski jumping was examined by both of the sensor data and the kinematical data in this study.

In this research we developed a wearable, augmented motion feedback system for ubiquitous training and motion assessment in mid-level ski jumping. Ski jump motion data captured with a set of inertial sensors were first transformed into meaningful kinematic motion information using an extensive processing system. Next, derived segment orientations, joint positions and joint angles were used to build and train motion knowledge on the base of the sport's common style and judging criteria. This intelligent machine knowledge was then applied to identify specific style information within incoming motion data that could be provided to the athlete as augmented motion feedback via a mobile training application. System validations on a set of test jumping data showed that style errors could be recognized and displayed well by the implemented system. We therefore believe the system to be suitable for the provision of kinematic motion feedback that could not be obtained without an extensive training support environment otherwise. Adding a real-time environment for athletesystem communication, this could lead to the creation of an ubiquitous training support application in future.

A ski jumping flight analysis was attempted on the basis of the high-speed digital video image taken at Hakuba Ski Jumping Stadium in Japan. Initial 40m of flights of 120-m jumping after take-off were recorded by a fixed high-speed video camera at a frame rate of 250 frames/s. After some corrections, a number of time series data were extracted for the loci of key parts of a jumper such as the waist, the ski boots and the ski tip as well as for key angles representing a jumper posture such as the ski angle and the forward leaning angle. It is demonstrated that the aerodynamic force data during real jumping flights, in particular in the early phase of a flight can be derived from video image.