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We hypothesised that high-accuracy players more linearly coordinate racket kinematics with impact heights under random height conditions than low-accuracy players. We compared the adjustments of racket kinematics according to impact height between high- and low-accuracy players. Fourteen male tennis players hit the incoming balls with a two-handed backhand at different impact heights (21-108% of body height) to a target area. The cluster analysis on accuracy divided participants into high- (

In Fiber Reinforced Plastics (FRP) molding, molds made of metal or epoxy resin blocks are commonly used, but the production time and material costs are high and not suitable for prototyping and small volume production. 3D printed molds have the potential to overcome these limitations, which would also enable frequent mold shape adjustment. The present study aimed to investigate the viability of the treated product as a mold for autoclave molding and establish a simple surface treatment method for additive manufacturing products produced by Fused Deposition Modeling. Polycarbonate resin was used to manufacture laminated male molds for the upper core and midsole of shoes, and the surface of the molds was treated with three different methods (clamping, treatment by aluminum tape and fluorine tape). The deformation of the molds due to autoclave molding was investigated by comparing the male molds before and after autoclave molding and computer-aided design data. In the clamping treatment, it was difficult to remove the mold after autoclave molding due to resin getting into the mold and fiber exposure due to resin loss was also observed. In the aluminum tape treatment, the midsole mold was deformed. On the other hand, the fluorine tape treatment enabled easy mold removal, and little deformation and weight change of the molds were observed. The results of this study suggest that the using laminated products made of polycarbonate resin can be used as molds for autoclave molding when combined with pre-treatment using fluorine tape.

Biomechanics (and energetics) of human locomotion are generally studied at constant, linear, speed whereas less is known about running mechanics when velocity changes (because of accelerations, decelerations or changes of direction). The aim of this study was to calculate mechanical work and power and to estimate mechanical efficiency in shuttle runs (as an example of non-steady locomotion) executed at different speeds and over different distances. A motion capture system was utilised to record the movements of the body segments while 20 athletes performed shuttle runs (with a 180° change of direction) at three paces (slow, moderate and maximal) and over four distances (5, 10, 15 and 20 m). Based on these data the internal, external and total work of shuttle running were calculated as well as mechanical power; mechanical efficiency was then estimated based on values of energy cost reported in the literature. Total mechanical work was larger the faster the velocity and the shorter the distance covered (range: 2.3–3.7 J m−1 kg−1) whereas mechanical efficiency showed an opposite trend (range: 0.20–0.50). At maximal speed, over all distances, braking/negative power (about 21 W kg−1) was twice the positive power. Present results highlight that running humans can exert a larger negative than positive power, in agreement with the fundamental proprieties of skeletal muscles in vivo. A greater relative importance of the constant speed phase, associated to a better exploitation of the elastic energy saving mechanism, is likely responsible of the higher efficiency at the longer shuttle distances.

The purpose of this study was to clarify the function of torques exerted by the joints of the lower trunk during maximal velocity sprinting. Eight male track and field athletes volunteered, and sprinted 60 m from a standing start position. The ground reaction force of the support leg was determined using a force platform (1000 Hz), which was placed at the 50-m mark from the start position. Simultaneously, 3D coordinates were recorded with a motion analysis system (250 Hz) using 20 cameras (MX-T20). The joint torques were calculated using inverse dynamics. The contribution of joint torques to the right and left hip joint forces, and the torso joint force, was calculated by a method that simultaneously solves equations of motion for each segment and equations of constraint conditions for adjacent segments connected by a joint. The main results were as follows: (1) During the terminal support phase (80-100% normalized time), the angular velocity of anterior rotation of the pelvis decreased and participants in whom this angular velocity decrease was diminished ran faster (p, Keyword: equation of constraint condition for adjacent segments connected by a joint

In this study, the kinetic characteristics of lower limbs during batting were investigated by comparing batting off a tee with batting a pitched ball. Participants were 10 male collegiate baseball players who performed tee batting (TB) and batting using a pitching machine (MB; approximate ball speed: 33.3 m/s). Three-dimensional coordinate data were acquired using a motion capture system, and ground reaction forces were measured using three force platforms. Lower limb joint torques were obtained by inverse dynamics calculations. The results indicated that the angular velocity of the lower trunk was larger in TB than in MB for rotation. The swing time from stride foot contact with the ground to ball impact was significantly longer in MB than in TB. The angular impulses of bilateral hip adduction, pivot hip external rotation, and stride hip and knee extension torques were significantly larger in MB, suggesting that batters exert these joint torques earlier for pitched balls to handle time constraints by changing the rotation of the lower trunk in response to the unknown ball location and speed in MB. These findings will help to fill a gap in the literature and provide coaching insights for improving batting motion.

The purpose of this study was to investigate effects of the ground reaction forces on the rotation of the body as a whole and on the joint torques of the lower limbs associated with trunk and pelvic rotation in baseball tee batting. A total of 22 male collegiate baseball players participated in this study. Three-dimensional coordinate data were acquired by a motion capture system (250 Hz), and ground reaction forces of both legs were measured with three force platforms (1,000 Hz). Kinetic data were used to calculate the moment about the vertical axis through the body's centre of mass resulting from ground reaction forces, as well as to calculate the torque and mechanical work in the lower limb joints. The lateral/medial ground reaction force generated by both legs resulted in the large whole body moment about its vertical axis. The joint torques of flexion/extension of both hips, adduction of the stride hip and extension of the stride knee produced significantly larger mechanical work than did the other joint torques. To obtain high bat-head speed, the batter should push both legs in the lateral/medial direction by utilising both hips and stride knee torques so as to increase the whole body rotation.

This study investigated the function of the upper extremities of elite race walkers during official 20 km races, focusing on the angular momentum about the vertical axis and other parameters of the upper extremities.Sixteen walkers were analysed using the three-dimensional direct linear transformation method during three official men's 20 km walking races. The subjects, included participants at the Olympics and World Championships, who finished without disqualification and had not been disqualified during the two years prior to or following the races analysed in the present study.The angular momenta of the upper and lower body were counterbalanced as in running and normal walking. The momentum of the upper body was mainly generated by the upper extremities. The joint force moment of the right shoulder and the joint torque at the left shoulder just before right toe-off were significantly correlated with the walking speed. These were counterbalanced by other moments and torques to the torso torque, which worked to obtain a large mechanical energy flow from the recovery leg to the support leg in the final phase of the support phase.Therefore, a function of the shoulder torque was to counterbalance the torso torque to gain a fast walking speed with substantial mechanical energy flow.

The purpose of this study was to investigate joint kinetics of the throwing arms and role of trunk motion in skilled elementary school boys during an overarm distance throw. Throwing motions of 42 boys from second, fourth, and sixth grade were videotaped with three high-speed cameras operating at 300 fps. Seven skilled boys from each grade were selected on the basis of throwing distance for three-dimensional kinetic analysis. Joint forces, torques, and torque powers of the throwing arm joints were calculated from reconstructed three-dimensional coordinate data smoothed at cut-off frequencies of 10.5-15 Hz and by the inverse dynamics method. Throwing distance and ball velocity significantly increased with school grade. The angular velocity of elbow extension before ball release increased with school grade, although no significant increase between the grades was observed in peak extension torque of elbow joint. The joint torque power of shoulder internal/external rotation tended to increase with school grade. When teaching the overarm throw, elementary school teachers should observe large backward twisting of trunk during the striding phase and should keep in mind that young children, such as second graders (age 8 years), will be unable to effectively utilise shoulder external/internal rotation during the throwing phase.

本研究では，球速の異なるボールに対する野球の打撃動作の特徴を明らかにすることで，打撃の正確性に影響を及ぼす動作要因について検討することを目的とした．球速の異なるボール（ 75km/h，100km/h，125km/h）を被験者に打撃させ， 3次元自動動作分析システムを用いて動作を計測した．打撃の正確性を評価する指標としてインパクト角を用いて，身体の並進および回転動作と打撃の正確性との関連について検討を加えた．その結果，ボール速度が大きい条件（ 125km/h）においては，身体重心の並進移動距離を小さくするとともに，上胴部およびバットの回転動作範囲を小さくすることが打撃の正確性を高める動作であると考えられた．さらに，体幹の捻り角度および捻り戻しの角速度の最大値にはボール速度条件による有意な差は認められなかったため，これらの動作はボール速度に関わらずスイングに必要な動作であると考えられた．

application/pdf, This study aimed to compare the muscle activities of the lower limb during overground level running (LR) and uphill running (UR) by using a musculoskeletal model. Six male distance runners ran at three running speeds (slow: 3.3 m/s; medium: 4.2 m/s; and high: 5.0 m/s) on a level runway and a slope of 9.1% grade in which force platforms were mounted. A musculoskeletal leg model and optimization were used to estimate the muscle activation and muscle torque from the joint torque of the lower limb calculated by the inverse dynamics approach. At high speed, the activation and muscle torque of the muscle groups surrounding the hip joints, such as the hamstrings and iliopsoas, during the recovery phase were significantly greater during UR than during LR. At all the running speeds, the knee extension torque by the vasti during the support phase was significantly smaller during UR. Further, the hip flexion and knee extension torques by the rectus femoris during UR were significantly greater than those during LR at all the speeds; this would play a role in compensating for the decrease in the knee extension torque by the vasti and in maintaining the trunk in a forward-leaning position. These results revealed that the activation and muscle torque of the hip extensors and flexors were augmented during UR at the high speed.

The purpose of this study was to investigate technical factors for maintaining skating velocity by kinematic analysis of the skating motion for elite long-distance skaters during the curve phase in official championship races. Sixteen world-class elite male skaters who participated in the 5,000-m race were videotaped with two synchronized high-speed video cameras (250 Hz) in a curve lane by using a panning DLT technique. Three-dimensional coordinates of the body and blades during the first and second halves of the races were collected to calculate kinematic parameters. In the group that maintained greater skating velocity, the thigh angle during the gliding phase of the left stroke during the second half was greater than that during the first half, and the center of mass was located more forward during the second half. Thus, it was suggested that long-distance speed skaters should change the support leg position during the gliding phase in the left stroke of the curve phase under fatigued conditions so that they could extend the support leg with a forward rotation of the thigh and less shank backward rotation.

This study analyzed the joint torque and the mechanical energy flow in the support legs of skilled male race walkers. Twelve race walkers were videotaped using a high-speed camera at a frame rate of 250 Hz set perpendicular to the sagittal plane of motion; their ground reaction forces were measured with two force platforms. A two-dimensional, 14-segment, linked model was used to calculate the kinetics of the support leg joints. In the initial part of the support phase, the mechanical energy flowed into the thigh and shank by the torque of the large hip extensors and knee flexors. In the middle part, the mechanical energy generated by the torque of the large plantar flexors flowed to the foot and from the foot to the shank by the ankle joint force. The mechanical energy flow by the forward joint force of the support hip was significantly related to the walking speed in the final part of the support phase. Our findings suggest that race walkers in the final part of the support phase should exert the torque of the knee extensors and hip flexors to transfer the mechanical energy more effectively to the support thigh and shank.

The purpose of this study was to investigate kinetic characteristics such as ground reaction forces (GRFs) and joint torques of the lower limb joints in downhill running for distance runners on overground. Six male distance runners were asked to run at three running speeds (3.3, 4.2, and 5.0 m/s) on the slopes of different grades (0, -3.2, -6.4, and -9.1 %) in which two force platforms were mounted. A two dimensional link model was used to calculate joint torques and joint powers of the lower limb joints. In spite that the downward velocity of the CG at the foot contact increased consistently as the grade increased, the impact peak of vertical GRF and the peak loading rate defined as maximum rate of change of the vertical GRF did not increase consistently as the grade increased. The runners on steep downhill conditions would be able to avoid excessive impact load by contacting with the ground in more extended hip position and increasing knee flexion velocity after the foot contact. The negative power of the knee after the foot contact was larger for -9.1 % downhill than the level condition, which revealed the eccentric load on the knee extensors increased in the steep downhill condition. The hip extensors exerted negative power with hip flexion just after the foot contact in -6.4 and -9.1 % downhill conditions so that the runners could absorb the impact force and mechanical energy.

The kinetic factors to maintain the curve skating velocity of long distance speed skaters were investigated by measuring the changes in blade reaction forces due to fatigue. Eight male long distance speed skaters performed 4000 m skating at maximal effort with an instrumented sensor klapskate. The skaters were videotaped with two synchronized video cameras (60 fields/s) in the mid portion of the curve by using a panning DLT technique. Push-off forces of the left leg and three-dimensional coordinates of the segment endpoints and blades during the left stroke over the 4000 m distance were measured at two points: 650 m and 3450 m. The blade reaction forces (BRF) were defined as the vertical and horizontal components in the coordinate system fixed on the ice, and used to calculate impulse. There were no significant differences in the peak value and impulse of the vertical component of the BRF between the measurements taken at the above two points while those of the horizontal component in the first half were larger than those of the second half. There were significant positive relationships between the peak value and impulse of the horizontal component and the velocity of the center of mass (r=0.721; 0.677, p

The purpose of this study was to investigate the mechanical energy flow in the recovery leg and its relationship to performance descriptors of elite male race walkers in an official race. Male race walkers participating in official 20 km races were videotaped with a VTR camera (60 Hz) set perpendicular to the course. The 28 elite race walkers (race records 1:19'50"-1:33'58") were selected as subjects. A two dimensional 14-segment linked model was used to calculate biomechanical parameters from the walking motion in the early phase of the race. The walking speed was significantly related to the step length but not related to the step frequency. Large mechanical energy flows at the hip occurred from the trunk to the foot during the first half of the recovery phase and from the foot to the trunk during the second half by the joint force power. Joint force powers at the hip in the second half of the recovery phase were significantly related to the walking speed and the step length. It is suggested that large joint force power at the hip would be one of the important factors to obtain high walking speed.

A simulation and optimization procedure was constructed to investigate the relationships between optimal movement and muscular strength for baseball pitching. Four segments (torso, upper arms, lower arms, hands) and six torque generators (shoulders, elbows, wrists) are modeled. The torque generators have torque-angle and torque-angular velocity characteristics of Hill-type muscle function. The optimization objective function includes release velocity and negative terms penalizing joint loading and inaccuracy. The weighting coefficient for joint loads has a strong influence on the results. As this coefficient increases, the motion becomes more similar to actual measured pitches. Combining active state patterns optimized for different weighting coefficients gives larger joint loads in the simulated motion. This supports the hypothesis that well-coordinated active states are important for controlling the relationships of the different torque generators in order to create a reasonable and effective pitching motion. The model proposed here is superior to previous simulations for throwing, from the viewpoint of modeling with characteristics of Hill-type muscle function, and can be used to explore realistic baseball pitching.