The purpose of this study was to investigate the body movements to generate handle velocity in the tangential and the radial direction of hammer head during the hammer throw turn. The positive leading distance of handle has the effect of accelerating the hammer head in hammer throw. In addition, the increase and decrease of the leading distance of handle are consistent with the increase and decrease of handle velocity in the radial direction of hammer head. It will be important to clarify the movement of the body for the acquisition of the leading distance of handle by examining the acquisition of the handle velocity in the radial direction by the body movement. Throwing motions of 44 male throwers (throwing record: 80. 50–44. 17 m) participated in the study as subjects. Throwing motions were videotaped on high-speed VTR cameras, and three-dimensional coordinates were calculated using a DLT method. The handle velocity was calculated as the vector products between the anatomical angular velocity vectors of joint and the respective relative displacement vectors from the joint center to handle, by applying a mathematical model. The handle velocity obtained by body movements were projected onto the rotating plane coordinate system. The basic findings were summarized as follows: (1) The handle velocity in the radial direction can be obtained by trunk long-axis rotation, the trunk left lean, the extension of the shoulder joint, the trunk back lean, and translational movement of the body. (2) The handle velocity in the tangential direction can be obtained by the trunk long-axis rotation, trunk twist, horizontal abduction of left shoulder joint and the flexion of shoulder joint.

For classic ballet dancers dancing on the narrow base of support, postural control ability is an important factor in evaluating their performance. We examined the hypotheses whether 1) postural control ability is related to the forefoot contact area on demi-pointe with one leg, and 2) the toe abductor muscle strength contributes to the larger forefoot contact area and postural control ability in classic ballet dancers. Eighteen junior female classic ballet dancers participated. Postural control time and the forefoot contact area were measured on demi-pointe with one leg. Furthermore, two types of measurements were performed to evaluate toe muscle strengths: the toe flexor strength and the toe abductor strength. In addition, the toe abductor muscle strength was calculated separately for the great toe abductor muscle strength and the little toe abductor muscle strength. There was a significant positive correlation between the forefoot contact area and postural control time (p<0.01), as well as between the little toe abductor strength and the forefoot contact area (p<0.01). These results revealed that the junior female classic ballet dancers, which can spread the forefoot contact area, can control the posture on demi-pointe with one leg for a long time. In addition, the little toe abductor muscle strength would affect the larger forefoot contact area.

The purpose of this study was to clarify the relationship between the change in direction of the velocity of center of mass (CoM) and the force acting on the center of mass during the take-off phase in a running single-leg jump (RSLJ) with different run-up speed and jumping task. Nine male collegiate jumpers performed RSLJ in two tasks, to jump forward and upward, respectively, with four different run-up speeds. Three-dimensional coordinates of the end positions of the body segments and the ground reaction force (GRF) were obtained using the motion capture system and force platform. The GRF and gravity acting on the CoM were divided into the normal and tangential force relative to the velocity of CoM. The amount of change in direction of CoM velocity was significantly correlated with the normal impulse during take-off phase. As run-up speed or take-off angle increase, the normal impulse and the negative tangential impulse increased in the first phase of take-off. The normal impulse in the second phase was decreased by the shortening of support time in the faster run-up speed. These results suggested that it is important for the change in CoM velocity direction to increase the normal force in the first phase of the take-off and it might be useful for the evaluation of the RSLJ by means of dividing the force into normal and tangential components relative to the velocity.

This study aimed to characterize basic postural recovery responses in younger adults before the first forward step landing (FL) after tripping in gait, or the pre-landing phase. Twelve young participants were tripped while walking and were required to return to normal walking after tripping. We recorded the kinematics and kinetics of their recovery responses using a 17-camera motion capture system and a force platform. We compared the whole-body angular momentum (WBAM) around the whole-body center of mass (WBCM) and the whole-body linear momentum (WBLM) in the tripping trials, with those in the normal walking trials. We also examined the angular momentum (AM) and linear momentum (LM) of the body segment groups and the joint torques. The forward WBAM around the WBCM increased by tripping started decreasing early in the pre-landing phase. When the forward WBAM decreased in the tripping trials, the backward AM of the tripped leg increased, while the increase in the forward AM of the head-neck plus trunk (HT) and support leg was suppressed. There was no significant difference in the forward WBAM around the WBCM at FL between the tripping trials and the normal walking trials. On the other hand, the forward and downward WBLM at FL were 1.1 and 2.5 times larger in the tripping trials than in the normal walking trials, respectively. In addition, all of the forward AM and the forward and downward LM of the HT at FL were significantly larger in the tripping trials. These results indicated that younger adults could decrease the forward WBAM increased by tripping to a level comparable to that at FL of normal walking. It is suggested that suppressing the increase in the forward angular velocity of the HT and support leg during a rapid forward swing of the tripped leg contributes to decreasing the forward WBAM around the WBCM. It is also suggested that although the WBAM changed due to tripping can be controlled during the pre-landing phase, suppressing the forward and downward WBLM as well as controlling the AM and LM of the HT after FL would be required for recovering to normal walking.

This study aimed to elucidate the role of joints and arm swing motion in controlling linear and angular momentum in vertical jumps. Twenty-eight participants performed maximal effort vertical jumps, and data on jumping motion (500 Hz) and ground reaction force (1000 Hz) were collected. The contributions of each joint torque to the linear and angular momentum of the whole body, arm, trunk, and leg were calculated by induced acceleration analysis. The role of the ankle joint torque was to acquire the vertical momentum of the whole body by external forces. The role of the knee joint torque was to regulate the horizontal and angular momentum of the whole body. The role of the hip joint torque was to distribute the momentum of the leg to the trunk by internal forces. The role of the virtual trunk joint torque was to distribute the angular momentum of the lower limb to the trunk by internal forces, and to control the distribution of horizontal momentum between segments. The arm joint torques did not affect the acquisition and distribution of these linear and angular momenta. However, the arm swing motion may have played a role as a counterweight to cancel the horizontal and angular momentum due to the motion-dependent forces acting on the whole body.

In baseball, the flight distance of batted balls is influenced by not only the batted ball velocity but also the spin. Previous studies reported that balls batted toward the opposite field (right field for the right-handed batter) had greater side spin and curved horizontally. If batters could impart less side spin to the ball, flight distance would be expected to increase because the ball would travel more linearly. The purpose of this study was to investigate how the spin of a batted ball is affected by the vertical bat angle at impact. A pitching machine was used to launch balls toward a fixed bat. The bat was positioned at six different angles under two conditions; the bat's long axis was adjusted horizontally and the bat head was declined 40° lower than the bat grip. The batted ball spins resulting from the batted ball angles were compared between the conditions. There were significant correlations between the horizontal batted ball angle and the side spin of the batted balls in both conditions. There was no significant difference between the slopes of the regression lines for the conditions. In brief, balls batted toward the same direction had similar spin regardless of the conditions. Therefore, it is suggested that the batters should not attempt to control batted ball spin, and increasing their bat swing speed would be still the most important key factor to hit balls long distances toward the various directions.

The purpose of the present case study was to clarify calligraphic skill of a Japanese calligrapher quantitatively. For this purpose, the brushwork of an expert calligrapher was kinematically compared with that of a novice as well as an intermediate. Three subjects (an expert calligrapher, an intermediate, and a novice) participated in the experiment. A motion capture system was used to capture the motion of a brush during writing a kanji on a Japanese writing paper. As results, absolute writing speed tended to fasten and the variability of the vertical displacement of a brush decreased along with the calligraphic skill. The frequency analysis of the horizontal velocity of a brush revealed that a dominant region shifted toward a low-frequency direction in the expert in comparison with the intermediate although their absolute writing speeds were not significantly different. These results suggest that the expert calligrapher could move the brush with rather slow than rapid change of velocity on the horizontal plane accompanying with lowering the vertical brush displacement.

The purpose of this study is to investigate the relationships between handle movement and leading distance of handle affecting increase and decrease of hammer head speed during turn phases. Forty-four male throwers (throwing record: 80.50－44.17m) participated in the study. Throwing motions were videotaped on high-speed VTR cameras, and three-dimensional coordinates were calculated using a DLT method. Kinematic parameter were calculated such as the hammer head speed, the leading distance of handle, the handle velocity in the rotating plane coordinate system where X_icr is the hammer head speed direction and Y_icr is the direction connecting the hammer head and the instantaneous rotation center. Fundamental factor were summarized as follows: (1) The increase and decrease of leading distance of handle was consistent with the increase and decrease of handle velocity in the Y_icr direction. That is, when the thrower pulls the handle toward the center of instantaneous rotation, leading distance that affects the hammer head speed increases as a result. (2) It became clear that the acceleration strategy for increasing the hammer head speed in the first half and the second half of the double support phases is different from the acquisition pattern of the leading distance of handle.

This study aimed to determine the heart rate and amount of physical activity of two differently skilled athletes while they were competing in amateur radio direction finding (ARDF). Heart rate and GPS data were measured in two athletes during a regional ARDF championship in Japan. Physical activity was estimated using GPS data and altitude derived from a map projection software. Results revealed that compared with the novice, the skilled athlete finished more quickly, covered a shorter distance, and experienced almost no stagnant phases (resting periods). The average heart rate for both athletes exceeded >160 bpm, which is of the same intensity as that found with high-level aerobic training. Additionally, heart rate variations, similar to those observed during intermittent training, were observed in both athletes. Finally, the energy expenditures during the competition greatly exceeded the recommended healthy exercise levels. In conclusion, despite the difference in the skill levels of the athletes, the measured heart rates and estimated physical activity during ARDF were extremely high. However, the difference in skill sets resulted in differences in the total distance covered, total time spent, and movement patterns.

The objective of this study was to identify the kinetic characteristics of the leg joints during the take-off motion of the kendo men strike and to investigate how these variables are related to take-off time in 20 male members of a university kendo team. The main results were as follows:

1.Subjects with shorter men strike times tended to also have shorter take-off times. In addition, the take-off time comprised 90% of the total men strike time.

2. The time taken by the three joints of the take-off leg to reach peak plantar flexion and extension torque, as a percentage of total take-off time, was 70.2±4.4% (ankle), 68.0±3.6% (knee), and 54.8±6.2% (hip).

Although there was no significant difference between the ankle and knee, the hip showed a tendency to reach the peak value earlier than the other two joints.

3.There was a significant correlation between deviations in the timings of torque exertion by the three leg joints and take-off time, with smaller deviations associated with shorter take-off times.

4.A significant correlation was observed between the take-off time and peak plantar-flexion torque at the ankle. No significant correlations were observed between take-off time and peak extension torque in the knee and hip or between peak positive torque power in the three joints and mechanical work.

The results of this study reveal the mechanical characteristics of the take-off motion unique to kendo and are useful for formulating training methods suitable for this action sequence.

We propose a new method for obtaining the three-dimensional angular velocity of a rotating sphere using one camera. This method has the following advantages: 1) it takes account of optical characteristics of the camera; 2) it needs only one camera; and 3) there is no restriction on the position of the camera (unlike the previous method in which the camera and the target coordinate system have to be aligned). The proposed method consists of the following steps. The angular velocity viewed from the camera is calculated using the geometrical relation between the trajectory of a point on the rotating sphere in the image and the camera condition (position and orientation). The angular velocity that is calculated in this step contains some errors because the image data is distorted due to the characteristics of the camera. Thus, the effect of the characteristics of the cameras canceled using an optimization calculation. At the same time, the angular velocity calculated in the first step is expressed in relation to a global coordinate system using a conversion based on the position and the orientation of the camera. The theoretical reasonability of the proposed and previous methods was verified using simulated data without any kind of noise, such as digitizing error. The result calculated by the proposed method was in good agreement with the ideal value. On the other hand, previous method contained some errors due to theoretical reasons. The proposed method was also tested by Bland-Altman analysis using experimental data obtained by a motion capture system which is regarded as a gold-standard method to check a practical accuracy. The proposed method showed good agreement with the gold-standard method.

In baseball hitting, the skill of the batter required to make a hit is high bat-head speed immediately before impact, accurate impact, and compact swing. Meanwhile, batting performance is affected by not only the batting techniques but also the bat mass and bat grip position. In addition, the influence of bat mass in youth players is thought to be greater than that in adult players. The purpose of this study was to investigate differences in the parameters of batting performance between the use of different bats at the moment of inertia (light or heavy bat) and normal or choked-up grip, and to provide the optimum bat and grip position for each batter. Fifty-seven youth (elementary and junior high schools) baseball players were asked to hit a baseball by using four types of bats. The hitting movement was recorded by using two high-speed cameras (1000 fps). Batting performance was evaluated by using eight parameters, including the speeds of the batted ball and bat, the bat trajectory, and the impact accuracy. Analysis of the principal component was conducted to find the condition maximizing each parameter. In 39 (68%) of the 57 subjects, the lightest bat was selected as the optimum condition. Of these subjects, 27 chose the choked-up grip condition. The main reasons for choosing the light bat and choked-up grip as optimal conditions were the increase in the angular velocity of the bat, the shortened travel distance of the bat head, and the shortened swing time. On the other hand, the optimal condition varied among players, and the parameters changed with the kind of bat chosen by each player. Meanwhile, when comparing the bat based on the ideal batted ball speed which is not influenced by impact accuracy, the heaviest bat was chosen from 9% of elementary school students. However, among junior high school students, the heaviest bat was chosen from 64% of total players. In conclusion, if the players choose a bat for the purpose of maximizing the hitting performance, youth players in the range of junior high school age, depending on their aim, can benefit from using the heavy bats whereas younger elementary school players tend to find the use of the light bat preferable regardless of their aim.

We aimed to investigate the generation and absorption of mechanical energy by the lower limb joints during the arm support phase of kicking pullovers. Thirteen men performed kicking pullovers, and the kinetics and kinematics of the hip, knee, and ankle joints were calculated between takeoff and upside position using a sagittal-plane, 10-segment, rigid body link model. The hip joint of the support leg generated the most energy by flexion torque and large flexion velocity of 331±66 deg/s. This joint was markedly extended at takeoff, which might have allowed for the large angular velocity and the expansion of the impulse by the ground reaction force before takeoff. These observations suggest that a series of movement skills including extension of this joint toward takeoff and rapid flexion of it immediately after takeoff is an important factor to achieve kicking pullover. The hip joint of the swing leg absorbed energy by exerting extension torque, suggesting that a part of the kinetic energy of the swing leg at takeoff was transferred to the trunk with this torque to facilitate the upward migration and backward rotation of the trunk. Hence, further studies on the energy transfer by the lower limb joints are required.

In baseball, an accurate impact of a ball with the “sweet spot” of the bat is absolutely imperative to slug the ball a great distance. Such a successful impact requires precise positioning of the bat in the right place at the right time. The purposes of this study were to determine the area on the bat in which the batted ball speeds were extremely high (the area defines sweet spot) and to describe the kinematic characteristics of the bat and the ball impact in the trials that the balls were hit outside the sweet spot (such a batting defines mishit). Twenty-six expert (collegiate or non-professional) baseball players were recruited and each player was asked to hit a baseball thrown by a pitching machine for 8–26 trials. Two high-speed cameras were used to record each hitting movement during the phase of ball impact at 1000 fps. Using the pool of data (the total of 1033 trials), the sweet spot was determined as the area in which the ratio of the batted ball to the bat head speed was higher than 1.13 (maximum value minus 0.05). The position of the ball at impact was represented as (a) the 3D position relative to the batsman’s body and (b) the 2D position relative to the bat-embedded reference frame. The results showed that the sweet spot was a 21×97 mm rectangle, having the center located at 145 mm from the bat head. The ball was hit successfully within the sweet spot in 341 trials and was mishit in 692 trials. In successful hitting, the ball thrown at the inside corner of the strike zone was impacted at a position closer to the pitcher than the balls thrown at the outside corner was impacted. In mishits in which the ball was hit more distal to the sweet spot, the 3D position of the ball at impact was located significantly closer to the pitcher’s side than in successful hitting. On the other hand, in mishits in which the ball was hit more proximal to the sweet spot, the 3D position of the ball was located significantly closer to the catcher’s side. Therefore, the accuracy of timing according to the pitching course is required for the successful hitting with the sweet spot of the bat.