By the standard, the discrimination of golf club can not be attempted concerning the flight-distance today. Then, the movement which intends to raise added value of golf club in feeling merit of the hitting sound is noticed. In this study, we made hitting sound prediction program for the purpose of predicting the hitting sound by design stage for attempting cost reduction in product development. In this paper, we describe the result of the utility of the hitting sound prediction program.

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Golf is one of the major sports, although there are problems, such as decrease of player and increase of aged bracket player. The driving distance of the golf club was extended by leaps and bounds by progress of technology. However, the flow which restricts driving distance is coming out in recent years. Moreover, the user is not necessarily choosing the club only with driving distance, and has become one of the elements also with an important hit ball sound. In this research, the fundamental characteristic of a club is investigated. Then, sample sound is created based on the obtained data. A questionnaire is performed and a target ideal sound is set up. It aims at finally finding out the structural conditions of the club for making a good hit sound.

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Batting sound of a metal baseball bat and a ball is discussed in this paper. The frequency of the sound is analysed and four resonance frequencies are measured for a sample bat. First two frequencies dominates the batting sound, so frequency ratio between two frequecies, difference of the amplitude at the resonance frequency, and damping coefficient for each resonance are examined in psychological tests to determine comfortable sound. Conssonant sound between two frequencies is better than dissonant sound even for impulsive sound. Suitable amplitude and suitable damping coefficient are also obtained by the experiment. In order to achieve the comfortable batting sound, the thickness of the bat was analysed and small modification is enough to improve the batting sound. It is also asserted that this modification does not effect on the the restitution coefficient.

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Requirement properties of metal baseball bats for horsehide were mainly coefficient of restitution and durability in the designing process. In recent years, another requirement property, hitting sound has been focused. Some researches concerning hitting sound comfort can be classified into 2 categories, one is sensual qualitative approach, the other is sound quality analysis such as 1/3 octave method. However these relationships has not been studied and the direct application of 1/3 octave method to the sound comfort evaluation is not proper. In this study, some problems in the application of typical sound analysis method are discussed and a new parameter, bsp, batting sound prominence, based on the loudness analysis method is proposed. The validity of the new parameter is discussed through the comparison with the sensual tests. Moreover the sound mechanism is also discussed.

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Recently, snowboard is one of the most popular winter sports in the world. When the snowboarder is gliding, the vibration occurs. For the professional snowboarders and amateur snowboarders, it is a serious problem that the vibration leads to player's difficulty to do edge control and gliding control on the snow surface. Then, the experimental modal analysis is applied to 5 snowboards. Vibration characteristics of each snowboards are identified, and analyze the cause of vibration of snowboard.

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Though the badminton can not be called the measure sports at present, they are the sports which hold considerable game population. However, in comparison with the tennis racket, the paper which studied the badminton racket is few, and it is not very much studied and has not been made. The research was carried out for the purpose of in this study, it does experimental mode analysis on the badminton racket, and examining the characteristic. In this study, by what kind of cause the characteristic difference of the racket that by using 2 rackets, of getting actually, that it is possible is said happened, was examined.

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Putter swing is modified by two link model and formulated by using 3 dimensional Newton-Euler. Then putter swing is measured by high speed camera and analyzed movement of joint by DLT method in order to obtain each angle between links. From these data torque of the joints are calculated. By using these torques effect of change of C.G. location and amount of moment of inertia on the putter is investigated. As the results it is known that effect of change of C.G. location is large but effect of change of moment of inertia is small.

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Fishing motion, that is, fishing rod, line, sinken and fish, are modeled by multi-body dynamics used links, strings and dampers. On the other hand, fishing motion is measured by taking a photograph with high speed camera and the joint motion and angle between links are digitized and represented by polynomial equation. More over the extension force of line when fish pull the line is measured. Then, fishing motion of a crucian fish is simulated. By using this simulation, fishing rod which a fish hung by hook does not easily release is investigated. Then it is known that the long rod is better than short rod. In the fishing, tip of a rod is usually in the water, then drag force of the rod in a water is large. So a rod which drag force is small is desired. It is known that to minimize the force, stiffness of tip of rod is smaller.

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A serious injury on being struck by a baseball pitch was reported recently. A baseball helmet is an integral part of the protective gear that prevents any head injuries upon being struck by a baseball. To improve the safety offered by the helmet, it is necessary to minimize the acceleration of the head. An appropriate choice of shell and liner materials would enhance the shock absorption capabilities of the helmet. In this study, the materials and thickness of the shell were varied, and an impact test was performed using a baseball launcher. The effect of the flexural properties of the shell materials on the acceleration of the dummy head, the pressure on its surface, and the energy absorbed by the shell were considered. Shell materials with high flexural modulus distributed the impact load, and reduced the acceleration and pressure that acted on the dummy head.

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The purpose of this study is to evaluate the mechanism of hip fracture of Japanese elderly female in fall during walking. Firstly we evaluated the characteristics of gait motion of elderly female by conducting volunteer tests. Based on the body motion of an elderly volunteer during a gait phase, we constructed a multibody-finite elemement hybrid model with gaiting postures and conducted fall simulations to evaluate the risk of hip fracture. Simulation results showed that the behavior of the falls of the elderly females is considerably different from those of the adult man and the risk of fracture at knee grounding at slip is significalntly higher than those of other fall conditions.

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It has not been clarified the reason why brain contusion tends to occur mostly at frontal part of a brain in each case that the impact is subjected at frontal or occipital part of the head. Therefore, the purpose of this study is to discuss a mechanism of cerebral contusion occurring at the impact site, called 'coup', and the site opposite the impact called 'contrecoup', from results of both experiments and simulations. Both a high-shape fidelity physical model of a human head and the Finite Element (FE) model were constructed from same medical images of a subject's head. Both high impact simulations in case of possible brain injury and low impact experiments were carried out to investigate intracranial pressure responses. The results showed that pressure concentrates at the frontal region more than the occipital region, which corresponds with clinical data.

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We investigate the characteristic behavior of the cervical vertebrae in automobile rear end impact collision simulation with mass production car seat (with headrest), compared with similar experiment with rigid metal seat (without headrest). By the rear end impact, body trunk goes forward and cervical vertebrae start to extend from lower level. But, by the inertia force of head, upper cervical vertebrae behaves flexion movement at first, then pass into hyperextension. Flexion of upper cervical spine and extension of lower cervical spine make whole cervical spine S-shaped sagittal malalignment. This unphysiological malalignment may cause conflict of zygapophysial joint and neck pain originated from that joint. Headrest may control the hyper extension of cervical spine and rear displacement of head, but cannot prevent from unphysiological S-shaped malalignment of cervical spine.

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Many researchers have studied the impact phenomenon in ball games, such as golf, tennis, baseball, soccer and so on. Although it is very important to understand the dynamic behavior of a ball on the impact phenomenon, the sufficient theoretical understanding of the behavior has not been obtained. In this paper, dynamics of hollow balls subjected to axial impact is theoretically analysed and the dynamic response of hollow balls is derived as an axisymmetric motion of an elastic spherical shell by using modal expansion method, where effects of area applied by impact force are took into account. The modal distribution of mechanical energies resulted by the work of half-sine axial impact force distributed uniformly in limited area are discussed.

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The purpose, in the present study, is to reproduce the behavior of the golf ball by FEM. For this purpose, we examined viscoelastic and elasticity behavior of butadiene rubber and thermoplastic ionomer, constituting golf ball. These data are necessary to reproduce the behavior of the golf ball by FEM. Therefore, we found some coefficients of elasticity and viscosity. With these coefficients, we search the coefficient of restitution of the golf ball. By the FEM analysis result, I got correlation of analysis and observed value in coefficient of restitution. In fact, We can reproduce the behavior of the golf ball by FEM.

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The aerodynamic characteristics of a three-dimensional body, such as sphere depend on the, form and surface structure of the body. It is known that a sphere's drag can be reduced by changing its surface structure. The purpose of this study is to clarify the relation of the drag and flow field to difference of the Shape of dimple. So, a diameter of the sphere is 42.6mm, 328 dimples are distributed on the sphere surface, and the shape of dimple are arc, cone and trapezoid. The drag, the pressure distribution and a detailed flow around the sphere clarified by the experiment and the numerical analysis that used turbulent flow model LES. As a result of an experiment and numerical analysis, the drag, the pressure distribution, the friction drag and the detailed flow pattern for arc, cone and trapezoid become clear.

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We investigated aerodynamic properties of a hard-baseball and a sphere by field experiments, in which we measure the trajectory of the projectiles using a high-speed video-camera. We determine the drag- and lift-coefficients by analyzing the video images. The drag coefficient (C_D) of the fastball pitch (back-spinning hard-baseball) with the spin parameter (SP)&ap;0.12, 0.23, decrease gradually with the Reynolds number (Re), for Re<1.4×10^5 and for Re<1.2×10^5, and attains its minimum at Re&ap;1.5×10^5 and Re&ap;1.2×10^5, respectively. Similarly, C_D of the back-spinning hard-baseball of SP&ap;0.35 attains its minimum at about Re&ap;0.8×10^5, increases gradually in the range 0.8×10^5<Re<1.3×10^5, and becomes almost constant for larger Re. In contrast, C_D of the back-spinning sphere with SP&ap;0.23 is almost constant for any Re considered. A rotating object placed in a uniform flow is subjected to the cross-flow force (Magnus effect), which lifts the back-spinning projectile upwards. We show that the direction of the Magnus force is inverted (negative Magnus effect) in a certain Re-SP parameter range, both for a hard-baseball and for a sphere.

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Using a high-speed video camera, we measured the trajectory and the rotation of a hard baseball thrown by a pitching machine, which can launch a rifle spinning 'gyro-ball'. We determined the drag coefficient by analyzing the video images. The drag coefficient of a 4-seam gyro-ball with the spin parameter (SP)&ap;0.12, 0.23 and 0.35, decreases gradually with the Reynolds number (Re). In contrast, the drag coefficient of a 2-seam gyro-ball with SP&ap;0.12 and 0.23 decreases in two steps. For SP&ap;0.12, it shows sharp decreases in the ranges 0.8×10^5<Re<1.0×10^5 and 2.0×10^5<Re<2.2×10^5 and it attains its minimum at Re&ap;2.2×10^5. Similarly, for SP&ap;0.23, the drag coefficient decreases in the ranges 0.7×10^5<Re<1.0×10^5 and 1.7×10^5<Re<1.8×10^5 in two steps, and attains its minimum at Re&ap;1.8×10^5. For SP&ap;0.35, it is almost constant below Re=1.3&ap;10^5 and attains its minimum at Re&ap;1.6×10^5 These findings confirm the occurrence of the drag crisis of Gyro-Balls. The different Re-dependence is due to the difference in seam patterns.

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A gyroball was actually pitched to investigate the influence of seam-positions. The differences due to the lift force were found in the trajectories of gyroball and fastball obtained by the high-speed video cameras. The gyroball dropped 20cm deeper than the fastball. However it was unable to distinguish the influence of seam-positions of gyroball in the trajectories. The drag coefficient can be estimated from the initial and final velocities of the pitched baseball which were obtained by the high-speed video cameras. The drag coefficients of the gyroballs were smaller than that of the fastballs. Furthermore, the drag coefficient for the 2seam-position was smaller than that for the 4seam-position.

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For improvement of pitching skill in baseball, it is important to understand the behavior of the pitched ball itself. This paper presents a method of detecting rotation of the pitched ball from image streams obtained by high speed camera. The ball was marked previously for helping image processing. Feature points from the image stream assemble into a set of linear equations that represents orientation change between consecutive two frames by rotation matrix R. The results from live pitching data are shown.

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To obtain a coefficient of restitution (COR) of an impact between baseball and bat from a mesurement using high speed video camera, a computer program for automated image processing is developed. In this program, an original image is transferred to edge detected image and a background except bat and ball region is removed. Template matching technique is employed to identify the locations of bat and ball. The value of COR is calculated from velocities of bat and ball which are derived from sequential location data. The automated image processing using the developed program is performed for several impact experiments. These results are compared with results obtained by manual image processing of the identical images and numerical analysis results by the finite element method. From this comparison, high accuracy and validity of the developed program are verified.

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The present study investigated the effects of pitch trajectory on batting swing. Balls of various trajectories were pitched to a professional baseball player and his batting motion was analyzed by the three-dimensional direct linear transformation (DLT) method. Acceleration applied to the bat during the swing was measured by installed accelerometers. Results were as follows: 1) Pitched balls with an inside trajectory had an impact point closer to the pitcher, while balls pitched with an outside trajectory had an impact point closer to the catcher. 2) Although the position of the bat at the point of impact changed for different pitch trajectories, there were no significant differences in the position of the waist or shoulder. The motion of the body during the batting swing, excepting the arms, was not affected by differences in pitch trajectory. 3) Ball pitched to waist height were hit with a higher bat head speed, resulting in a greater post-impact flight distance. 4) Batters appeared to adjust their batting swing to the pitch trajectory just prior to impact.

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The purpose of this study is to establish the measurement system that enables easily kinematics analysis of lower limb of baseball batting form and to evaluate its kinematics. The measurement system consists of the 6-axis force sensor that measures reaction force from the fields, 3-axis gyro sensor and 3-axis acceleration sensor to obtain the movement data of lower limb. We can obtain the angular velocity of joint and reaction force by using this measurement system, and estimate the joint torque of pivoting foot from inverse dynamics analysis using Newton-Euler formulation. It is found that the joint torque of pivoting foot clarifies the difference between experiences and beginners. Therefore, this measurement system can analyze the major features of pivoting foot in baseball batting and this method may be able to quantitatively evaluate the skill of the batting.

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The lightweight racket with head-heavy configuration is recent tendency of high-tech rackets, increasing power with an increasing racket swing speed. Racket frames as light as 200 grams have appeared in the market. However, the predicted results showed that the lightest racket at present in the market has advantageous for racket head speed, but disadvantageous for coefficient of restitution, rebound power, and post-impact velocity for ground stroke, and it has also large shock vibrations at the racket handle compared to the ordinary super-light weight racket. This means a limit to the weight lightening of tennis racket from the viewpoint of performance. The engineers and racket designers at the racket companies seem to be under intense pressure to keep pumping out new and better technologies every year. This paper investigated the physical properties of the biggest racket appeared in the market that was banned by ITF rules several years ago, predicting racket performance in terms of impact shock vibrations of player's wrist joint, which might be related to the feel. It is based on the experimental identification of the racket-arm dynamics and the simple nonlinear impact analysis. The result showed that the magnitude of shock vibration at the handle and the wrist joint with the biggest racket is rather small compared to the recent representative racket. Prediction and estimation of power will be reported in a separate paper.

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Currently, the terms used in describing the performance of a tennis racket are still based on the feel of an experienced tester or a player. However, the optimum racket depends on the physical and technical levels of each user. Accordingly, there are a number of unknowns regarding the relationship between the performance estimated by a player and the physical properties of a tennis racket. The lightweight racket with head-heavy configuration is recent tendency of high-tech rackets, increasing power with an increasing racket swing speed. Racket frames as light as 200 grams have appeared in the market. However, the predicted results showed that the lightest racket at present in the market has advantageous for racket head speed, but disadvantageous for coefficient of restitution, rebound power, and post-impact velocity for ground stroke, and it has also large shock vibrations at the racket handle compared to the ordinary super-light weight racket. This means a limit to the weight lightening of tennis racket from the viewpoint of performance. The engineers and racket designers at the racket companies seem to be under intense pressure to keep pumping out new and better technologies every year. This paper investigated the physical properties of the biggest racket appeared in the market that was banned by ITF rules several years ago, predicting racket performance in terms of the coefficient of restitution, the rebound power coefficient, and the post-impact ball velocity relevant to the power of the racket. It is based on the experimental identification of the racket dynamics and the simple nonlinear impact analysis. The predicted results could explain the difference in mechanism of performance between the the biggest racket and the recent representative racket. The biggest racket provides higher coefficient of restitution particularly at the topside of string face, higher racket head speed and higher post-impact velocity compared to the recent representative racket. Prediction and estimation of feel will be reported in a separate paper.

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Tennis is played by very wide people. So, various kinds of rackets are demanded. As a result, to develop various kinds of rackets in a short term has become necessary. However, the phenomenon of the impact between the racket and the ball is very complex, so the analysis is difficult. In this research, the impact between the racket and the ball was studied experimentally. The behaviors of the ball during the impact were analyzed using high speed images. According to the experimental result, the following conclusions can be obtained. There are three processes in the rotational speed of the ball during the impact. The rotational speed of the ball after the impact increased with increasing the displacement of the ball in the parallel direction to the surface of the strings. The rotational speed of the ball decreased with increasing the displacement of the slide of the ball.

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Impact simulations were performed to observe the vibration characteristics of a tennis racket and its strings, plus the effects on the hand. The 3-dimensional modeling of the tennis racket was achieved using CATIA V5, and included the modeling of the frame, strings, and rubber grip. The simulations were performed using ABAQUS explicit. As a result, the deformation characteristics of the tennis racket and its effect of on the hand were clarified in relation to the frame boundary conditions, different string tension, and different impact locations for the ball on the racket.

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Fitting is really important function for footwear designing, regardless of users' skills and use condition. Generally, in order to enhance the fitting function, it is focused on last designing based on statistical foot data. However, fitting under the wearing condition varies depending on upper structures. Especially, it is dramatically changed after fastening shoelace. The purpose of this study is the proposition of fitting evaluation method under the wearing condition. By using optical 3D deformation analysis system, normal displacement of upper surface was directly measured under wearing condition. Then, we proposed DI (out-plane Displacement Index), which was calculated from normal displacement of upper surface. As a result of comparison of DI and sensual test, the validity of DI was checked. Furthermore, relationship between fitting under wearing condition and foot type was discussed.

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Trail running which means running on non-flat surfaces is getting popular these days. In this trail running, runners can select the slope and running surface. This means that runners can select any running condition. The foot motions in trail running and flat surface running are quite different. The direct application of sole stability designing method based on flat running to trail running designing is not proper. In the sole stability evaluation, 3 dimensional motion capture system is frequently used. However the measurement in the open air is attended with difficulty. In this study a simple stability evaluation method using an accelerometer is proposed. In surfaces with various slopes, the validity of the proposed method is checked. Moreover the relationship between sole stiffness and stability on the trail running is also discussed.

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Recently, more and more runners run on not only a jogging course but also a treadmill in a fitness club or their houses. Different footwear functions on treadmill running with overground running are required because of quite deferent running conditions. The purpose in this study is to clarify the basic elements to design the specific footwear for treadmill running. It is focused on that the difference of foot motion in the overground and the treadmill running. Reafoot evertion angle (β), tibial internal rotation angle (γ) and foot plantar pressure distribution were measured under the treadmill running and overground running. As a result of the motion analyses, it was confirmed that treadmill running produced the shorter step width, larger foot angle to the running direction, smaller maximal β(β_<max>,) and γ(γ_<max>), and smaller foot plantar force. As increasing running speed, β_<max> was also increasing and γ_<max> was decreasing. It was suggested that the treadmill running might reduced the risk of running injuries for not only over-pronators but also under-pronators.

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On the overall cushioning characteristics of sport surface and sole, a interaction exists between the cushioning caused by viscoelastic deformation and the one caused by sliding friction. The characteristics has come investigation with the instrument that can be measured sliding friction force and velocity under landing impact.

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Long pile artificial turf (3G turf) is becoming a popular sports surface and its "Shock Absorbency" has been approved by the conventional DIN test. However, it has been suggested that the conventional test do not reflect actual loading caused by human sports action. This study aims to re-examine how much the current, standard DIN test is valid to evaluate the shock absorbency of the 3G turf and to establish a new testing procedure precisely reflects the acute human load. The conventional DIN test was found to be inappropriate to evaluate the shock absorbency of high loading condition like hard landing by human (from 50cm height). In contrast, the newly developed testing rig succeeded in reproducing such high loading, in which the difference of shock attenuation property between the 3G turfs was clearly illustrated. The need of high loading test using an alternative testing procedure was highlighted.

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The purpose of this study is to construct a finite-element (FE) model which can accurately simulate the behaviour of golf impacts, and to investigate the effect of a shaft on clubhead upon the rebound behaviour of a ball, by conducting an FE analysis of a ball colliding with a simplified club. The clubs were constructed by holding the simplified clubheads by the locking ring which is fitted onto a steel shaft. Three clubheads (circular hollow bodies) of constant mass, made of a titanium alloy, with increasing loft angle were manufactured based upon the mass, volume and position of centre of gravity (COG) of commercial clubheads. The FE models of the clubheads, which consisted of clubheads, locking ring and shaft, with linear elasticity, were constructed. The FE model of the ball consisted of 8-node solid elements, and the material model was expressed as a viscoelastic model with hyperelasticity. Impact experiments were also conducted to confirm the accuracy of the FE models, by comparing the results of the experiments to those of the FE analyses. The results of impact simulations closely matched the experimental results. The impact behaviour was analysed by varying the impact point of the ball colliding with the full clubs and the singular clubheads; the results for the collision between the ball/clubs and ball/clubheads were compared. The difference between the two extreme values for the rebound angle and the spin rate in the case of the club impacts tended to become smaller than that of the clubhead impacts. This tendency is estimated to depend on the relationship between the shaft position and the loft angle/COG of the clubhead.

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This paper describes the influence of a golf club head's angle of attitude on aerodynamic forces. Three drivers' club heads were tested in a wind tunnel. The first shape is like a rectangular parallelepiped, the second shape is like a squarish circle, and the last one is intermediate. The wind speed was 30m/s, and the club head's angle of attitude was taken as a parameter. The results are summarized as follows: The aerodynamic forces depend on the attitude of the driver's head. The drag depends on not only the projectile area of the head, but also the position of the boundary-layer separation.

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We hereby report, through calculations and physical experiments, on how the angle of the club-head actions changes immediate before an impact when being swung if CG characteristics of the heads vary. The distance between the shaft axis and the CG location of the club-head is resolved into Loft and Lie angle variable components and we examined the relation of the angle of club-head actions to each component. FEM analysis is used to calculate a shaft bending angle and recognize it as an angle of club-head actions. The angle of the club-head actions is measured from the swings of several test golfers and compared the relation between calibration head and the test heads. Through this procedure, we found that the calculated value and tested value are resulted almost same.

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Lure fishing and fly-fishing have been positioned as sports deliberately different from the traditional Japanese fishing-style. In the case of fly-fishing, casting is the element which anglers must master in order to cast a fly, done so by using the weight of a line. This study uses experimental and computational analysis to investigate the dynamic behavior of a fly line. Fly-fishing constitutes various elements, but the importance that casting holds is extremely large. Fling speed, the casting process and the loop shape of the line while in flight are important for the proper presentation of flies. Moreover, the shape of a fly line is also important for a long cast or controlled cast. However, it is difficult to grasp the phenomenon or to make a numerical model because a fly line is an object of flexible string. Therefore, the most suitable casting method will be clarified from the viewpoint of sports engineering and human dynamics. In addition, measuring an angler performing movements with a flexible object such as a rod or a line is difficult. So establishing a method to measure the dynamic behavior precisely is also one of the purposes of this study. For the past study, casting that uses only one hand have been analyzed. However, casting that uses both hands is often done in the actual fishing field. In this paper, line's behavior is examined in double haul casting.

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The aim of this study was to visualize and to analyze the wake of a swimmer's dolphin kick in a horizontal and a vertical (sagittal) plane using two-component PIV (2C-PIV). PIV allows us to visualize the unsteady flow field instantaneously and to estimate the fluid force. One trained male swimmer was instructed to maintain a swimming position with dolphin kicking in a swimming flume at the flume velocity of 1.2m/s. Results of both horizontal and vertical plane showed the pairs of vortices and jet flow between them. The vortices induced by the dolphin kicking motion seemed to be three-dimensional structure. It was plausible that the dolphin kicking motion performed in this study generated a propulsive force by generating the vortex pair and the jet flow as a reaction force.

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Flow fields around a swimmer are extremely unsteady. Top swimmers are expected to swim using effectively unsteady flow force. Particle Image Velocimetry (PIV) can visualize the unsteady flow field around swimmer's hand. A motion analysis can evaluate the unsteady motion of swimmer quantitatively. In the traditional study, however, PIV and a motion analysis were carried out individually. In this study, we construct a synchronized system of two methods, and apply the system to a front crawl swimmer, in order to clarify the relationship between the motion of swimmer's hand and the vortex generated from it at the same time. To combine two methods, we illuminated swimmer's hand with the red lights, and separated the light by passing it through Laser Line Band Pass Filter and Red Band Pass Filter for PIV (532±2nm) and for High-speed camera (640〜700nm), respectively. To get synchronized images, we reconciled the first shutter timing in the methods using a pulse generator and setting the shutter period to 72ms in PIV and 8ms in a motion analysis. By applying the synchronized system to a swimmer, we succeeded in getting images synchronized by 72ms.

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Generation of propulsive force in swimming was investigated. In knowing the mechanism of the generation unsteady character of flow is impotant, and the conventional quasi-unsteady theory cannot give the correct understandings on the the generating mechanism of the propulsive force. The role of vortex is critical in the generation of momentum and therefore in that of force. Swimmers generate strong vortices by the motion of pitching and heaving motion of hand. In the motion the spped of hand is not necessarily fast, the magnitude and the direction of the induced velocity due to vortices are crucial.

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The purpose of this study was to investigate the relationship between plantar flexion angle and underwater dolphin kick performance by simulation model SWUM (SWimming hUman Model). The input data were obtained by the anthropometric and motion analysis using 2-D DLT method to compute unsteady fluid forces, buoyancy and gravity acting on the swimmer. To recreate the swimming dynamics on the simulation, fluid coefficients, used to calculate the unsteady fluid forces, were identified to minimize the difference between measured and simulated swimming velocity by the least-squares method. Simulations of the increased plantar flexion angle were executed with the optimal fluid coefficients. The results show the swimming velocity increased due to the increment of the thrust generated by the feet after increasing the plantar flexion angle. Furthermore, it was suggested that the flexibility of plantar flexion is important, though it is not a determinant factor of the underwater dolphin kick performance.

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The objective of this study was to develop a system which enables athlete swimmers and coaches to easily understand the swimming motion in their daily training. In this system, a tri-axial acceleration and gyroscopic sensing unit is worn by the swimmer. From the measurement results by the sensing unit, the original swimming motion is reconstructed by a developed software. In addition, the fluid force acting on the forearm and hand can be estimated by the software, utilizing the technique of our swimming human simulation model SWUM. In this paper, the system structure, reconstructing method of swimming motion, an experiment to validate the accuracy of the system, and the developed software for displaying the swimming motion are described.

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This paper describes a new strength training method. We introduced a concept of Specified Area (SA) into the strength training. And we investigated the possibility of strengthening the SA using a new training load that combined isoviscous load and elastic load. One male subject completed fully elbow flexion in two loading manners which were the isoviscous load (3.0, 5.0, 8.0, 12.0, 20.0, 30.0[Nm/(rad/s)]) and the combination load. The combination load of this study was the load changing from isoviscous load (8.0[Nm/(rad/s)]) to isoviscous load (8.0[Nm/(rad/s)]) adding elastic load (10.0[Nm/rad]) during the motion. The comparison of these results implied the possibility of the SA strengthening using our proposed training method.

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