YANAI, Toshimasa

ISSN：10658483

Outline：© 2017 Human Kinetics, Inc. We developed a force measurement system in a soil-filled mound for measuring ground reaction forces (GRFs) acting on baseball pitchers and examined the reliability and validity of kinetic and kinematic parameters determined from the GRFs. Three soilfilled trays of dimensions that satisfied the official baseball rules were fixed onto 3 force platforms. Eight collegiate pitchers wearing baseball shoes with metal cleats were asked to throw 5 fastballs with maximum effort from the mound toward a catcher. The reliability of each parameter was determined for each subject as the coefficient of variation across the 5 pitches. The validity of the measurements was tested by comparing the outcomes either with the true values or the corresponding values computed from a motion capture system. The coefficients of variation in the repeated measurements of the peak forces ranged from 0.00 to 0.17, and were smaller for the pivot foot than the stride foot. The mean absolute errors in the impulses determined over the entire duration of pitching motion were 5.3 N·s, 1.9 N·s, and 8.2 N·s for the X-, Y-, and Z-directions, respectively. These results suggest that the present method is reliable and valid for determining selected kinetic and kinematic parameters for analyzing pitching performance.

ISSN：0484-6710

Outline： A wide range of topspin rotation of a bat around the long-axis, referred to as “rolling”, has been observed in baseball batting, but the mechanical reasons for the large variability among individual batters has not been examined. The purpose of this study was to investigate the factors determining this variability in rolling velocity among professional baseball players. Twenty-nine professional batters each performed eight “free-batting” trials. An electromagnetic tracking device was used to measure the three-dimensional rotational motion of the bat in each trial. The rolling velocity was 678±376°/s, comprised a negative contribution attributable to the batter's effort of exerting torque (Mechanism 1; −1144±488°/s) and a positive contribution attributable to the gyroscopic effect (Mechanism 2; 1808±339°/s). A significant positive correlation (r=0.67, p<0.05) was found between the rolling velocity and the negative contribution of Mechanism 1. These results indicate that (a) the torque exerted by the batter resists the rolling and that (b) a higher rolling velocity is attained by batters who exert a smaller resistive torque on the bat than those who exert a larger torque. On the other hand, no correlation (r=0.09) was found between the rolling velocity and positive contribution of mechanism 2. These findings suggest that the batter makes an active effort to resist rolling, and that the amount of resistive torque exerted by the batter is the primary reason for the inter-individual difference in rolling velocity attained at the instant of ball impact. As the resistive torque is likely to be exerted by the nobside hand in the form of pronation torque (Ae et al. 2015) and the pronation causes lowering of the bat-head (increasing nutation angle), a reduction of the pronation torque should decrease the resistive torque acting on the bat, helping to attain a high rolling velocity. In fact, we observed a greater deceleration of nutation velocity in the fast-rolling group than in the slowrolling group (p<0.05). To attain the high rolling velocity, therefore, we suggest that batters should aim to build up the nutation velocity of the bat until about 50 ms before ball impact, and then vigorously decelerate it immediately before ball impact.

ISSN：10658483

Outline：© 2016 Human Kinetics, Inc. Although the lift force (F L ) on a spinning baseball has been analyzed in previous studies, no study has analyzed such forces over a wide variety of spins. The purpose of this study was to describe the relationship between F L and spin for different types of pitches thrown by collegiate pitchers. Four high-speed video cameras were used to record flight trajectory and spin for 7 types of pitches. A total of 75 pitches were analyzed. The linear kinematics of the ball was determined at 0.008-s intervals during the flight, and the resultant fluid force acting on the ball was calculated with an inverse dynamics approach. The initial angular velocity of the ball was determined using a custom-made apparatus. Equations were derived to estimate the F L using the effective spin parameter (ESp), which is a spin parameter calculated using a component of angular velocity of the ball with the exception of the gyro-component. The results indicate that F L could be accurately explained from ESp and also that seam orientation (4-seam or 2-seam) did not produce a uniform effect on estimating F L from ESp.

ISSN：10658483

Outline：© 2016 Human Kinetics, Inc. Low back pain is a common problem among competitive swimmers, and repeated torso hyperextension is claimed to be an etiological factor. The purpose of this study was to describe the three-dimensional torso configurations in the front crawl stroke and to test the hypothesis that swimmers experience torso hyperextension consistently across the stroke cycles. Nineteen collegiate swimmers underwent 2 measurements: a measurement of the active range of motion in 3 dimensions and a measurement of tethered front crawl stroke at their maximal effort. Torso extension beyond the active range of torso motion was defined as torso hyperextension. The largest torso extension angle exhibited during the stroke cycles was 9 ± 11° and it was recorded at or around 0.02 ± 0.08 s, the instant at which the torso attained the largest twist angle. No participant hyperextended the torso consistently across the stroke cycles and subjects exhibited torso extension angles during tethered front crawl swimming that were much less than their active range of motion. Therefore, our hypothesis was rejected, and the data suggest that repeated torso hyperextension during front crawl strokes should not be claimed to be the major cause of the high incidence of low back pain in swimmers.

ISSN：0484-6710

Outline： In this study, we analyzed the kinematic characteristics of various types of baseball pitches by elite baseball pitchers, and tested a null hypothesis that “no type of pitch has the same kinematic characteristics as another.”
 A high-speed video camera was used to record the initial trajectory of the pitched ball thrown by 84 skilled baseball pitchers. Each pitcher was asked to throw all the different types of pitch he would use in competition and practice, and to self-declare the type of pitch used for each throw. The kinematic characteristics of each pitched ball were analyzed as ball speed, the direction of the spin axis, and the spin rate. A custom-made device was used to analyze the direction of the spin axis and the spin rate, and the ball speed was measured with a radar gun. One-way ANOVA with the Games-Howell post hoc test was used to test the hypothesis.
 The total of 364 pitches were categorized into 11 self-declared pitch types. Four of 10 pitch types thrown by more than one pitcher - the four-seam fastball, slider, curveball and cutter - had unique kinematic characteristic distinct from all of the other pitch types. No significant differences were found in any of the kinematic parameters between 1) changeup and sinker, 2) forkball and split-fingered fastball, and 3) two-seam fastball and shoot ball. Therefore, the hypothesis was retained for these 3 pairs of pitch types: although they were kinematically similar, the pitchers categorized them as different types.
 When the breaking ball was compared with the four-seam fastball, they were classifiable into 3 types: 1) pitches with a slower ball speed and lower spin rate with a different direction of spin axis (changeup, sinker, forkball and split-fingered fastball), 2) pitches with a slower ball speed, different direction of the spin axis and a spin rate comparable to the four-seam fastball (slider, curveball and cutter), and 3) pitches with a comparable ball speed, similar spin axis direction, and lower spin rate (two-seam fastball and shoot ball). These data revealed that the kinematic characteristics of some pitch types are quite different from those described in baseball coaching handbooks.

Outline：The purpose of this study was to extract key impact parameters that determine the horizontal direction of batted ball trajectory in opposite-field hitting. Three-dimensional finite element analysis method was used to construct an impact model between a baseball and a wooden baseball bat, and a series of simulations with various bat swing direction and impact conditions were conducted. Horizontal bat angle was set -31〜20° and vertical bat angle was set 0〜51°, and each was analyzed at the 3° interval. The line of impact was set inclined in the range of 0〜40° with a 5° interval. The velocity and the angle from horizontal and from center line of the batted ball immediately after impact were determined for each simulated condition. The simulation model was validated by comparing the simulation outcome with experimental data obtained from opposite-field hitting practice performed by collegiate baseball players. The result showed that the horizontal angle of the bat at impact is the most impact parameter to determine the horizontal direction of batted ball trajectory in opposite-field hitting. In addition, the combination of the vertical bat angle and the angulation of the line of impact condition is also an important parameter. It is possible, therefore, to hit a ball toward a given horizontal direction with many different combination of horizontal bat angle, vertical bat angle and the angulation of the line of impact.

Outline：The purpose of this study was to examine the factors influencing the position of "sweet spot (the impact position that maximizes batted ball speed)" of baseball bats. A finite element analysis was used to construct an impact model between a baseball and a wooden baseball bat, and a series of simulations were conducted with various bat swing speed and impact conditions. The simulation outcome showed two characteristic phenomena: One phenomenon is that, in the case of increasing the linear momentum of the bat, batted ball speed decreases when impact position offset from the node of bat 1st bending mode particularly the position that offset in the direction of the bat end. The other phenomenon is that, in the case of increasing the angular momentum of the bat, batted ball speed that impact position offset in the direction of the bat top from the sweet spot became higher than the speed when impact position is the node.

Outline：The rotation of the golf-club around the long-axis of the shaft may be generated by two mechanisms. The 1^ mechanism is the angular impulse exerted by the golfer around the long-axis of the shaft directly. The 2^ mechanism is the change in the orientation of the long-axis of the shaft with respect to the angular momentum of the golf-axis of the shaft in golf swing. A golfer performed 5-trials of "place shot" toward target away from 2m of the golfer. The electromagnetic tracking device was used to measure the three-dimensional motion of the golf-club. The angular velocity around the shaft was 1938±211°/s in the direction of "closed face" at ball impact. The angular velocity attributed to 1^ mechanism was 3543±378°/s in direction of "opened face", on the other hand the angular velocity attributed to 2^ mechanism was 5400±312°/s in direction of "closed face" at impact. These results suggest that the angular impulse exerted by the golfer around the long-axis of the shaft be important to control the direction of the face.

Outline：The purpose of this study was to examine the three-dimensional kinematic parameters of ball impact that cause the phenomenon of the lateral deviation of the batted ball. Nineteen women's collegiate softball players performed four "free-batting" trials with maximal effort to project the batted ball toward various directions; fly or line drive toward same field, grounder toward same field, fly ot line drive toward opposite field, and grounder toward opposite field. Behavior of the ball impact was recorded with two high speed cameras (1000 fps). Three-dimensional trajectory of the batted ball was calculated using the initial condition of the batted ball (velocity of the batted ball, spin rate, orientation of spin axis) immediately after impact. The projection angles of the bat on the horizontal plane (horizontal bat angle), the vertical plane (vertical bat angle) and the angle from horizontal of the line of impact (line of impact angle) were determined at the ball impact. Laterally-deflected distance of batted ball in opposite-field hitting (6.01±1.85 m) was longer than same field hitting (2.23±1.75 m). Meanwhile, within-group variance of laterally-deflected ratio (laterally-deflected angle per second) varied widely. The laterally-deflected ratio was correlated with the horizontal bat angle and the line of impact angle, but the vertical bat angle was not. The results indicate that the laterally-deflected ratio of the batted ball was increased by if the impact surface of the bat is facing toward the direction of the batted ball at the instant of ball impact.

Outline：In this study, we developed a system measuring bat behavior during a baseball swing by mounting an inertial sensor unit which incorporated the acceleration sensor and the gyro sensor to bat grip end. We compared the bat behavior that measured by between developed system and three-demensional motion capture system (MAC3D system; Motion Analysis). As a result, accuracy of the bat behavior calculated by developed system was varified. Furthremore, we defined eight parameters to express a characteristic of the bat behavior. In this way, players and coachers can evaluate baseball swing quantitatively. Eight parameters are "swing time", "swing speed (impact)", "swing speed (max)", "impact acceleration", "rolling", "bat radius of rotation", "bat angle" and "swing orbit".

ISSN：03933660

Outline：Aim: The purpose of this study was to examine kinematic differences between faster and slower sprinters during the acceleration phase of sprint running. Methods: Nineteen collegiate sprinters were divided into FAST (N.=9) and SLOW (N.=10) groups, based on their best 100 m race times. A two-dimensional videographic technique was used to record the side views of 40 m sprint performances using four high-speed digital camcorders. Using the recorded images, kinematic variables such as contact time, flight time, horizontal velocity, and horizontal acceleration were determined from the 1 st step to the 19 th step. A two-way repeated measures ANOVA (two groups of 10 steps each) with a Tukey post-hoc test was used to analyze the obtained data. Results: From the 7 th step to the 19 th step, the horizontal velocity was significantly higher for the FAST group as compared with that for the SLOW group. The horizontal acceleration from the 1 st step to the 19 th step and the horizontal velocity from the 7 th step to the 19 th step were significantly greater for the FAST group as compared with those for the SLOW group. In addition, the ground contact time was significantly lower for the FAST group as compared with that for the SLOW group. Conclusion: The results indicate that faster sprinters can achieve greater horizontal acceleration with shorter ground contact during the initial as well as the latter stage of the acceleration phase, during which they are already running faster.

ISSN：0363-5465

ISSN：1476-3141

ISSN：0966-6362

ISSN：0484-6710

Outline：In baseball, batters occasionally aim to hit the ball toward the opposite field. Players and coaches generally believe that the impact surface of the bat needs to face toward the opposite field at the instant of ball impact, so that the ball makes an oblique impact with the bat and bounces off toward the opposite field. Photograms and video recordings of opposite-field hitting, however, often give an impression that the impacting surface of the bat does not necessarily face toward the opposite field. Therefore, there may be an overlooked mechanism for opposite-field hitting. The purpose of this study was to examine the kinematic parameters of ball impact that determine the direction of the struck ball in opposite-field hitting. Sixteen collegiate baseball players performed ten trials of opposite-field hitting, and the movements of the ball and bat before, at, and after impact were recorded with three high-speed cameras (1000 fps) for three-dimensional analysis. The projection angles of the bat on the horizontal plane (horizontal bat angle), the vertical plane (vertical bat angle) and the angle from horizontal of the line of impact (line of impact angle) were determined at the instant of ball impact. The struck ball travelled toward the opposite field at 23.0±7.5° from the center line of the field. Whereas the mean value of the horizontal bat angle was 6.7° toward the opposite field, the bat was facing towards the center and the same field in 16.4% of all trials. These results indicate that the batter can hit the ball toward the opposite field even if the impact surface of the bat is facing toward the center or the same field at the instant of ball impact. In this paper, we reveal an additional mechanism for hitting the ball toward the opposite field.

ISSN：0484-6710

Outline： The purpose of this study was to determine how runners sprinting along a curved path could rotate their whole-body about the vertical axis to keep facing towards ever-changing movement direction. Ten healthy men were asked to run at 5 m/s along a straight path (RS) and a curved path with a 5-m radius (RC). The running direction in RC was counterclockwise (CCW) as viewed from above. A motion capture system with eight cameras was used to record the three-dimensional coordinates of reflective markers attached to each subject with the sampling frequency set at 240 Hz. The angular momentum of each body segment about the vertical axis passing through the center of mass of the entire body was determined for one complete stride cycle with the method described by Dapena (1978). The average value for the angular momentum of the entire body about the vertical axis was determined for each contact phase and each flight phase. Two-way ANOVA (2 movements×4 phases) was used to test the significance of the main and interaction effects. In addition, the angular momentum was categorized into head and trunk, right leg, left leg, right arm, left arm, both arms and both legs, and the pattern of change in each category during the normalized stride cycle was compared between two movements. Two-way ANOVA demonstrated a significant main effect for both factors with no interaction. In all phases, the average angular momentum in RC was directed more toward CCW as viewed from above than that in RS. Whereas the angular momentum of the head and trunk in RS changed periodically from positive to negative values, that in RC maintained positive values throughout the stride cycle. The angular momentum of the right leg in RC changed periodically in the same phase as in RS, but that of the left leg changed in the reverse phase. The left leg not only moved back and forth in RC, but also moved from side to side, allowing it to undergo circular motion in a direction opposite to the body's rotation in the horizontal plane. Presumably, this circular motion generated reaction effects on the adjacent segments, causing the head and trunk to gain sufficient angular momentum to keep facing toward the running direction.

Outline：The purpose of this study was to describe instantaneous moment arms of the scapular rotators during arm elevation. Thirteen male subjects performed humeral elevation in the scapular plane. The locations of the origin and insertion of the scapular rotators (trapezius, pectoralis minor, rhomboid and serratus anterior) was determined using the existing skeletal model of the scapula and thorax. Based on the helical axis, the instantaneous scapular rotation axis were computed. Then, the instantaneous moment arms of the scapular rotators relative to the scapular rotation axis were calculated. During humeral elevation, the lengths of the moment arms were changed depending on the muscle fascicles. Only the serratus anterior had muscle fascicles whose moment arms were opposite for the scapular rotation in the same muscle. These results indicate the functions of scapular rotators for scapular rotation during humeral elevation.

Outline：The purpose of this investigation was to develop a method for calculating contributions of the force-couple system applied to the baseball bat to the orientation of the bat at ball impact. A collegiate baseball player was asked to perform tee-batting in a direction toward the center field. A motion capture system operating at 500 Hz was used to determine three-dimensional coordinates of reflection markers attached to the bat. The resultant force and the resultant moment exerted on the bat by the batter's hands were determine with the inverse dynamics approach and their contributions to the orientation of the bat were computed with the forward dynamics approach. Horizontal angles and vertical angles of the bat calculated with the forward approach were in excellent agreement with the kinematically measured angles of the bat. A sample analysis of collegiate baseball player indicated that the horizontal and vertical angles were produced by the positive contributions of the couple moment that exceeds the negative contributions of the moment of resultant force.

Outline：In baseball batting, it's important to send a high speed ball. To do it, batters are required to accelerate bat head hugely and to hit a ball accurately in space and in time. This study focused on mistimed batting. Four hypotheses are tested: mistimed batting occurs due to (1) the influence of the ball image thrown previously, (2) delayed start of the swing, (3) delayed arrival of the bat at the ideal impact position because the bat head speed didn't increase enough before impact, and (4) delayed arrival of the bat at the ideal impact position because swing trajectory was longer. Six collegiate baseball players were asked to hit pitched balls of three different speeds (120km/h, 130km/h, 140km/h) toward the center field in 2 conditions. In the first condition, they hit several balls of a given speed repeatedly until they think they hit the ball in the way they evaluate best. In the second condition, they hit 35 balls thrown at various speeds without being informed of the ball speed. Ball projection order was pre-determined by the examiner to include five patterns: (1) 10km/h up (2) 20km/h up (3) 10km/h down (4) 20km/h down (5) Speed keep. The results showed that mistimed batting occurred most frequently at 140km/h fast ball and the factor 2 was most common reason for it. This result supports the instruction that baseball coaches often says "you should swing early."

ISSN：10658483

Outline：The purpose of this study was to investigate how the contraction-induced increase in distal biceps brachii tendon moment arm is related to that in elbow flexor muscle thickness, with a specific emphasis on the influence of the site-related differences in muscle thickness. The moment arm and muscle thickness were determined from sagittal and cross-sectional images, respectively, of the right arm obtained by magnetic resonance imaging of nine young men. The muscle thickness was measured at levels from the reference site (60% of the upper arm length from the acromial process of the scapula to the lateral epicondyle of the humerus) to 60 mm distal to it (every 10 mm; 7 measurement sites). At 80° of elbow flexion, the moment arm and muscle thickness were determined at rest and during 60% of maximal voluntary contraction (60%MVC) of isometric elbow flexion. Only the relative change from rest to 60%MVC in muscle thickness at the level 60 mm distal to the reference site correlated significantly with that of the moment arm. This result indicates that the contraction-induced increase in distal biceps brachii tendon moment arm is related to that in elbow flexor muscle thickness near the corresponding muscle-tendon junction. © 2014 Human Kinetics, Inc.

ISSN：0021-9290

ISSN：1746-1391

ISSN：1050-6411

ISSN：1065-8483

ISSN：01959131

Outline：PURPOSE: Muscle hypertrophy in response to resistance training has been reported to occur nonuniformly along the length of the muscle. The purpose of the present study was to examine whether the regional difference in muscle hypertrophy induced by a training intervention corresponds to the regional difference in muscle activation in the training session. METHODS: Twelve young men participated in a training intervention program for the elbow extensors with a multijoint resistance exercise for 12 wk (3 d·wk). Before and after the intervention, cross-sectional areas of the triceps brachii along its length were measured with magnetic resonance images. A series of transverse relaxation time (T2)-weighted magnetic resonance images was recorded before and immediately after the first session of training intervention. The T2 was calculated for each pixel within the triceps brachii. In the images recorded after the session, the number of pixels with a T2 greater than the threshold (mean + 1 SD of T2 before the session) was expressed as the ratio to the whole number of pixels within the muscle and used as an index of muscle activation (percent activated area). RESULTS: The percent activated area of the triceps brachii in the first session was significantly higher in the middle regions than that in the most proximal region. Similarly, the relative change in cross-sectional area induced by the training intervention was also significantly greater in the middle regions than the most proximal region. CONCLUSION: The results suggest that nonuniform muscle hypertrophy after training intervention is due to the region-specific muscle activation during the training session. Copyright © 2013 by the American College of Sports Medicine.

Outline：The purpose of this study was to describe the characteristics of the ball impact in soccer volley kick. Nine experienced male soccer players performed volley kicks. The ball was projected by soccer machine at three speeds (9.0m/s for Low speed condition: 11.5m/s for Middle speed condition: 15.0m/s for High speed condition). The volley kick performances were recorded with three high-speed cameras. Ball velocity after impact had a significant correlation with the foot velocity in each speed condition. Ball-foot speed ratio (= ball speed after impact / foot speed before impact) had a quadratic relation to the impact point of the ball on the foot along the short-axis and it was high when the ball impact point was near the mid-sagittal plane of the foot.

Outline：In baseball batting, the horizontal direction to which the batted ball will project is influenced by two factors; (a) the direction to which the impacting surface of the bat is facing at ball impact and (b) the interaction of the inclination angle of the bat in the vertical direction and the position of the ball impact along the short axis of the bat. The purpose of this study was to describe the three-dimensional orientation of baseball bat at ball impact for each direction (same, center, and opposite field) of batted ball. Forty-seven elite baseball players performed 7-36 trials of free-batting. Behavior of the ball impact was recorded with two high-speed cameras (2500 fps). All trials in which the bat collided with the ball, including the foul balls, were used for the analysis. The orientation of bat at ball impact was described as the azimuth angle and the depression angle of the bat's long-axis. Frequency distribution maps were constructed to display the probability of hitting the ball toward the same, center and opposite fields for each combination of azimuth and depression angles of the bat at ball impact. The frequency distribution maps illustrate that a unique zone exists for each direction of the batted ball and that the zones overlap substantially. These results suggest that batters can hit the ball toward the three directions even if the orientation of bat at ball impact was same.

ISSN：0039906X

Outline：The present study aimed to investigate how the morphological and mechanical properties of Achilles tendon change in adolescent boys. Twenty-nine adolescent boys and 12 male adults participated. Ultrasonography was used to measure Achilles tendon elongation. The transition point, that is, the intersection point of the "Toeδ and "Linearδ regions was determined from tendon elongation-tendon force relationship, and the stiffness and Young's modulus of the Achilles tendon were calculated from linear region. The hysteresis was calculated as the ratio of the area within the tendon elongation-tendon force loop to the area beneath the load portion of the curve. The stiffness, Young's modulus and stress at transition point were greater in adults (544 ± 231 N/mm, 1.6 ± 0.7 GPa, 23 ± 6 MPa) than in adolescents (374 ± 177 N/mm, 1.1 ± 0.7 GPa, 19 ± 10 MPa). However, no differences were observed in the tendon length and the tendon cross-sectional area and stress at transition point between adolescents (174 ± 23 mm, 60 ± 11 mm 2 , 6.1 ± 2.0 %) and adults (180 ± 30 mm, 63 ± 7 mm 2 , 5.5 ± 2.2 %). The hysteresis in adolescents (20 ± 18 %) was greater than that of adults (12 ± 10 %). These results suggest that the morphological properties of Achilles tendon are similar between adolescents and adults, but that mechanical properties are altered with growth to become a stiffer and more spring-like structure.

ISSN：0039906X

Outline：The present study aimed to investigate how the morphological and mechanical properties of Achilles tendon change in adolescent boys. Twenty-nine adolescent boys and 12 male adults participated. Ultrasonography was used to measure Achilles tendon elongation. The transition point, that is, the intersection point of the "Toe" and "Linear" regions was determined from tendon elongation-tendon force relationship, and the stiffness and Young's modulus of the Achilles tendon were calculated from linear region. The hysteresis was calculated as the ratio of the area within the tendon elongation-tendon force loop to the area beneath the load portion of the curve. The stiffness, Young's modulus and stress at transition point were greater in adults (544 ± 231 N/mm, 1.6 ± 0.7 GPa, 23 ± 6 MPa) than in adolescents (374 ± 177 N/mm, 1.1 ± 0.7 GPa, 19 ± 10 MPa). However, no differences were observed in the tendon length and the tendon cross-sectional area and stress at transition point between adolescents (174 ± 23 mm, 60 ± 11 mm², 6.1 ± 2.0 %) and adults (180 ± 30 mm, 63 ± 7 mm², 5.5 ± 2.2 %). The hysteresis in adolescents (20 ± 18 %) was greater than that of adults (12 ± 10 %). These results suggest that the morphological properties of Achilles tendon are similar between adolescents and adults, but that mechanical properties are altered with growth to become a stiffer and more spring-like structure.

ISSN：2193-1801

ISSN：1065-8483

ISSN：1340-8682

Outline：Lower birth weight has been associated with lower cardiorespiratory fitness（CRF）and muscular strength in later life. The aim of this study was to examine whether physical activity may modify associations of birth weight with CRF and muscular strength in children, as well as the relative contributions of birth weight and current physical activity levels to the fitness. The subjects were 535 elementary school children aged 7-12 years. Data were collected on current weight and height. Birth weight was reported according to the Maternal and Child Health Handbook records. CRF was measured by a 20 metre shuttle run test and muscular strength was assessed by grip strength. Information on physical activity was obtained by a questionnaire filled by parents, which asks weekly time spent on habitual exercise activity（min/week).We calculated the time spent in exercise activity higher than 3 METs as moderate to vigorous physical activity（MVPA）and higher than 6 METs as vigorous physical activity（VPA). Lower birth weight was associated with lower CRF（β = 0.087, p = 0.010), after adjustment for sex, months of age, schools, and current height and body mass index（kg/m²). This association was little changed by MVPA（β = 0.090, p＝0.008）or VPA（β = 0.088, p = 0.007), however, VPA was a stronger predictor of CRF than birth weight（β = 0.237, p ‹ 0.001). Birth weight was not associated with muscular strength. The results showed that the association of birth weight with CRF was not modified by physical activity levels in childhood. However, VPA was found to be a stronger predictor of CRF than was birth weight, suggesting that physically active lifestyle which focus on vigorous intensity activity may have a much more important role in development of CRF than an individualʼs low birth weight.

Outline：The purpose of this study was to investigate the relationship between the flight trajectory of the ball and ball spin in various kinds of baseball pitch. Each subject thrown various kinds of their own pitches for three throws each. The pitched balls were recorded using 4 high-speed video cameras. The flight trajectory, ball spin rate, and direction of spin axis were obtained from the video images, and hypothetical flight trajectory with free fall was calculated from ball initial velocity. Equations were obtained to estimate the displacement of the flight trajectory from that of the free fall ball using "decomposed spin parameter" which consists of the ball spin rate, direction of spin axis, and initial velocity (p<0.001). The findings showed that the displacement of the flight trajectory depended on the ball spin rate and direction of spin axis, thereby accurately predictable from the spin. The characteristics of ball spin can be utilized to develop a strategy to alter the flight trajectory.

Outline：The "opposite-field hitting" is enabled by hitting the ball with the bat angled horizontally and facing its impacting surface toward the opposite field (the first mechanism: conventional theory). Theoretically, the batters can adopt other approach to successfully hit the ball toward the opposite field: Assuming that the batter hits the lower part of the ball with a bat positioned horizontally and facing toward the center field, the batted ball should travel upward toward the center field. If, however, the bat facing toward the center field is tilted downward to position the head slightly lower than the grip, the batted ball should travel upward and toward the opposite field (the second mechanism). The present study was conducted to determine the contributions of these mechanisms in opposite-field hitting. The 146 trials were analyzed and found that the contribution of the second mechanism (69%) was greater than the first (31%).

ISSN：1050-6411

Outline：:This study aimed to clarify the influence of the intensity of a conditioning contraction on subsequent isometric twitch and maximal voluntary concentric torques. Subjects (n=12men) performed voluntary isometric plantar flexion for six seconds as a conditioning contraction, at intensities of 40%, 60%, 80% and 100% of a maximal voluntary isometric contraction (MVIC). Before and immediately after the conditioning contraction, isometric twitch and maximal voluntary concentric (180°/s) plantar flexion torques were determined. Surface electromyograms were recorded from the triceps surae muscles and M-wave amplitudes and root-mean-square values of the electromyographic signals (RMS(EMG)) were calculated. The isometric twitch torque increased significantly after conditioning contraction at all intensities (P<0.05), whereas maximal voluntary concentric torque increased significantly only at 80% and 100% MVIC conditions (P<0.05). It is concluded that during a six second conditioning contraction, the effect of the intensity of a conditioning contraction on subsequent torque development is different between an isometric twitch and maximal voluntary concentric contractions, with the latter being less affected.

ISSN：0021-9290

ISSN：0148-639X

ISSN：1439-6319

ISSN：1439-6319

ISSN：1065-8483

ISSN：0195-9131

ISSN：0195-9131

ISSN：0484-6710

Outline：The purpose of this study was to test the hypothesis that the position of the center of buoyancy (CB) relative to the center of mass (CM) lay more caudally when the abdominal breathing technique is used, as compared with the chest breathing technique. Ten healthy men who practiced the abdominal and chest breathing techniques participated. The position of the CB, CM, and the distance between them (CB-CM distance) were determined as time-series data during inhalation with each breathing technique, and the changes in the positions and distance due to inhalation were compared between the two techniques. The results showed that both the CB and CM translated due to the inhalation and that the amount and direction of the translations differed between the two techniques (p<0.01). The increase in the CB-CM distance was significantly smaller (p<0.01) with abdominal breathing (1.11 cm) than with chest breathing (1.21 cm). For both breathing techniques, the CB was located more cranially to the CM, regardless of the amount of inhalation. These data demonstrate clearly that the position of the CB relative to the CM lies more caudally with the abdominal breathing technique than with chest breathing, thus supporting our hypothesis. These results indicate that breathing technique influences the magnitude of the moment of buoyant force around the CM and the swimmer's ability to float horizontally on the water surface.

ISSN：1530-0315

Outline：PURPOSE:The purpose of the present study was to examine a hypothesis that the musculotendinous behavior during a propelling action with a countermovement can be altered by a single practice session through modulation of neuromuscular activities.;METHODS:Eight males performed unilateral maximal plantarflexion with (CMJ) and without (noCMJ) countermovement before and after a practice consisting of six sets of three repetitions of unilateral CMJ exercises. Measurements included EMG activities of the triceps surae and tibialis anterior muscles and the fascicle behavior of the gastrocnemius by ultrasonography, and impulse was calculated from the force-time data. The change in tendon length was also estimated.;RESULTS:The impulse in CMJ increased after the practice, but that in noCMJ did not. After the practice, the magnitude of fascicle lengthening and shortening in CMJ decreased, which was accompanied by an increase in tendon shortening without change in the ankle joint range of motion. The time lag from the onset of reaction force to that of EMG activities of the triceps surae muscles was shortened after the practice.;CONCLUSIONS:The results support the hypothesis and indicate that, as a neural modulation through a single practice, the muscle-tendon unit behavior during CMJ can be optimized to improve the performance.

Outline：The purpose of this study was to investigate the relationship between angular velocity of the bat and movements of upper limbs. Nine hitters performed free-batting practice. An electromagnetic tracking device was used to record three dimensional kinematic data of the thorax, the humerus and the forearm of the both side and the bat. The results showed that sequential rotation, in order of the thorax, the shoulder, the elbow and forearm, was observed on the lead arm for all subjects. All joint range of motion on the push arm were larger than that on the lead arm. There was a significant correlation between swing angular velocity and shoulder range of motion for horizontal abduction on the lead arm. No correlation was founded between the rolling angular velocity and body movements, indicating that the magunitude of the rolling angular velocity is not associated with the range of each joint motion and the timing of sequential action.

Outline：The purpose of this study was to investigate the effectiveness of the torso and upper extremity rotation for producing the bat-swing velocity in baseball batting. Seventeen male collegiate baseball players were asked to perform the batting trials using a batting-tee. Three-dimensional kinematic data were recorded by an optical motion capture system operating at 500Hz. The rigid link model consisting of five segments (pelvis, thorax, shoulder girdle, upper extremity and bat) developed to calculate the contribution of the torso and upper extremity rotation to producing the bat-swing velocity. In the early swing phase, the contribution of the pelvic rotation around the vertical axis was larger than the rotation of other segments. In the late swing phase, the contribution of the rotation of the upper extremity relative to the shoulder girdle and the bat relative to the upper extremity around the vertical axis were large.

Outline：The purpose of this study was to examine if the escalation of leg-sinking effect of buoyancy around the center of mass (CM) during breathing changes due to different breathing patterns -- chest breathing and abdominal breathing. Five male participated in this study. The positions of the CM, the position of the center of volume (CV), and distance between CM and CV were determined. The results showed that CV-CM distance increased for 1.47cm with chest breathing and for 0.94cm with abdominal breathing. As a result of these change of distance, the leg-sinking effect increase for 10.27Nm with chest breathing and for 6.40Nm with abdominal breathing. The small leg-sinking effect decrease the energy cost of swimming. The results of this study indicates that abdominal breathing reduces the leg-sinking effect of buoyancy, suggesting that abdominal breathing may improve the performance of swimming.

Outline：The purpose of this study was to describe three-dimensional scapular translation and rotation during arm elevation. Thirteen male subjects performed humeral elevation in the scapular plane. The location of the center of mass (CoM) of the scapula was determined using the existing skeletal model of the scapula. Based on the helical axis, the scapular rotation axis were computed. During humeral elevation, a) the position of the CoM of the scapula relative to the thorax moved superiorly and medially, b) the lateral (upward) rotation and posterior tilt angles of the scapular attitude were changed at a constant rate, c) the orientation of the scapular rotation axis was nearly constant, d) the location of the scapular rotation center on the scapula moved medially from the acromion. These results indicate the mechanical relationship in which the time-history of the rotation axis orientation and position determine the attitude and position of the CoM at any given instant during the scapular motion of interest.

ISSN：0039906X

Outline：In this study, we examined applicability of existing equations to predicting the body surface area (BSA) of children, and newly developed prediction equations for the BSA of children. BSA of 87 children of both genders (7 ∼ 12 yr) was determined by the three-dimensional photonic image scanning (3DPS), which was used as reference. BSA predicted using existing equations yielded overestimation or underestimation and/or a systematic error with respect to the reference. BSA prediction equations for boys and girls were developed using height and body mass as independent variables for the validation group and cross-validated for another group. The standard errors of estimation of the prediction equations were 105 cm 2 (0.9 %) for boys and 158 cm 2 (1.4 %) for girls. In the cross-validation group, there was no significant difference between the predicted and measured values without systematic errors. These findings indicate that existing equations cannot accurately predict BSA of children, and that the newly developed prediction equations are capable of predicting BSA of children with adequate accuracy.

ISSN：0039906X

Outline：In this study, we examined applicability of existing equations to predicting the body surface area (BSA) of children, and newly developed prediction equations for the BSA of children. BSA of 87 children of both genders (7∼12 yr) was determined by the three-dimensional photonic image scanning (3DPS), which was used as reference. BSA predicted using existing equations yielded overestimation or underestimation and/or a systematic error with respect to the reference. BSA prediction equations for boys and girls were developed using height and body mass as independent variables for the validation group and cross-validated for another group. The standard errors of estimation of the prediction equations were 105 cm² (0.9 %) for boys and 158 cm²(1.4 %) for girls. In the cross-validation group, there was no significant difference between the predicted and measured values without systematic errors. These findings indicate that existing equations cannot accurately predict BSA of children, and that the newly developed prediction equations are capable of predicting BSA of children with adequate accuracy.

ISSN：1050-6411

ISSN：0148-639X

ISSN：0039-906X

ISSN：0021-9290

ISSN：1348-1509

Outline：The acromial-sensor-tracking protocol with an electromagnetic tracking device is a non-invasive measurement protocol for recording the three-dimensional scapular movement continuously. In the present study, the orientations of motionless scapula were determined with the acromial-sensor-tracking protocol and the magnitude of the measurement error attributable to the skin-movement was assessed non-invasively by the landmark-digitizing protocol with the digitizer. Three sensors of the electromagnetic tracking device were attached to the skin overlaying the sternum, acromion and humerus, and three or more bony landmarks for each segment were manually digitized with the stylus to define the anatomical meaningful orientation. After the initial digitizing, the subject was asked to maintain the arm at five positions. While the subject was maintaining the arm, the orientation of the scapula was determined simultaneously by the attached sensors and by the directly digitizing of the scapular bony landmarks (the landmark-digitizing protocol). The mean values for the root mean square (RMS) errors representing the differences in the measured scapular orientation between the acromial-sensor-tracking protocol and the landmark-digitizing protocol across the five humeral abduction angles were found to be <5.2°. The magnitude of the measurement error exhibited in acromial-sensor-tracking protocol was substantially smaller than the range of the scapular movement exhibited during the humeral abduction. The results demonstrate that the acromial-sensor-tracking protocol is a valid measurement protocol to describe the three-dimensional continuous scapular movement with sufficient accuracy.

ISSN：0387-5008

Outline：The purpose of this study was to examine the factors influencing the behavior of the baseball during and after the impact with a wooden bat. A finite element approach was used to model the behavior of a baseball and a wooden bat at the impact and the linear and angular velocities of the ball after the impact were determined for given sets of impact condition. The simulation outcome was validated with 22 sets of actual measurements taken during a "free batting practice" performed by the members of a collegiate baseball team.

ISSN：13494414

Outline：The present study examined the influence of the duration of a conditioning contraction inducing postactivation potentiation on the extent of increase in subsequent maximal voluntary concentric torque. Nine male subjects performed a 6 s or 14 s maximal voluntary isometric plantar flexion as the preceding conditioning contraction. Before and immediately after the conditioning contraction, the twitch torque and maximal voluntary concentric torque were recorded. The twitch torque significantly increased in the 6 s and 14 s conditions. The twitch torque after the 14 s conditioning contraction was significantly larger than that after the 6 s conditioning contraction (p < 0.05). Electromyogram recodings indicated that central fatigue was larger in the 14 s condition. These results suggest a tradeoff of the negative (fatigue) and positive (potentiation) effects that can mask the resultant increase in voluntary torque, when the conditioning contraction is performed beyond a certain duration.

ISSN：1097-4598

Outline：:The purpose of this study was to compare the extent of twitch potentiation (TP) after stimulated or voluntary contractions at identical intensities for the human knee extensor muscles. Isometric knee extensions of 10 s were performed at 20%, 40%, and 60% of maximal voluntary contraction (MVC) torque level, through percutaneous electrical stimulation of the quadriceps at 80 Hz or voluntary contraction. Twitch responses were evoked by stimulating the femoral nerve percutaneously with supramaximal intensity. The extent of TP after the stimulated contraction was greater than that after the voluntary contraction at the 20% MVC torque level, whereas a stimulated contraction induced a smaller extent of TP than did a voluntary contraction at contraction intensities higher than 40% MVC. We suggest that this contraction intensity dependence of differences in TP after stimulated and voluntary isometric conditioning contractions is responsible for differences in the recruitment pattern of motor units during the conditioning contractions.

Outline：The spin of a pitched baseball affects the ball trajectory which relates to pitchers' performance. We investigated the relationship between the motion of the fingers and the spin rate of pitched baseball. Five professional and three collegiate pitchers participated in this study. The motions of ball, hand and fingers during the ball release were recorded by 3 high-speed video cameras. We defined the amount of angle that the fingers actually rotated the ball as "back spin angle". The ball spin rate was correlated to 1) the amount of extension at PIP joint of the index finger (p<0.05) and the middle finger (p<0.01) and 2) the back spin angle (p<0.01). These results suggest that delaying the ball release is an effective way to increase the ball spin rate, but pitchers are limited to change their timing of the ball release since the timing also determines the projection angle. We concluded that ball spin rate, ball velocity and ball spin axis angle are interrelated with each other under the restriction of throwing the ball into the strike zone.

Outline：The purpose of this study was to examine the influence of the rolling angular velocity of the bat on batted ball characteristics. In order to construct the model of the bat and ball and to simulate of the ball-bat impact phenomenon, numerical analysis programs based on the three-dimensional finite element method was used. In this study, to focus on the rolling angular velocity of the bat, the simulation was conducted at a constant pitched condition. The rolling angular velocity of the bat was set at 200,1000,1800 [°/s] based on 22 sets of actual measurements taken during a "free batting practice" performed by the member of a collegiate baseball team. The results showed that as the rolling angular velocity of the bat is increased, maximum flight distance does not change, whereas maximum kinetic energy is slightly increased.

Outline：The purpose of this study was to investigate the relationship between angular velocity of the bat and movements of upper limbs. Three left-hand hitters performed toss-batting practice. An electromagnetic tracking device was used to record three dimensional kinematic data of the thorax, the humerus and the forearm of the leading side and the bat. The results of this study showed that sequential rotation, in order of the thorax, the humerus, the forearm, was observed for all subject. The subject who recorded the fastest swing angular velocity tended to attain large range of motion in shoulder horizontal abduction and elbow extention. The subject who recorded the fast rolling angular velocity tended to attain large range of motion in shoulder external rotation and forearm supination. These results suggested that sequential motion and the joint range of motion of the leading upper limb might be related to the angular velocity of bat.

Outline：The purpose of this study was to describe the time-course of change in the orientation of the longitudinal axis of the runner's body passing through the center of mass (CM) during the maximum-effort sprinting on a curved runway. Ten male collegiate sprinters were asked to sprint along the 2nd lane on an official 400m track. The performances were recorded with four high speed cameras. The DLT algorithm was used for 3D reconstruction and the longitudinal axis of the whole body passing through the CM was calculated. The results showed that the longitudinal axis of the whole body maintained a forward (5.8±1.9°) and inward (14.1±2.2°) leaning-position during the entire stride cycle. The orientation, however, fluctuated during the stride cycle; the longitudinal axis leaned toward inward direction by 3.6±0.7° during right contact phase and toward outward direction by 2.8±0.6° during left foot contact phase. These results indicate that the ground reaction force exerted on the body during each contact phase generated rotational motion about the antero-posterior axis in the opposite direction in curved sprinting.

ISSN：01959131

Outline：PURPOSE: The purposes of this study were (a) to describe the detailed movements of the shoulder complex during the cocking phase in tennis serve and (b) to determine the contribution of the scapular rotation to the peak shoulder external rotation attained at the end of the cocking phase. METHOD: Twenty tennis players performed flat tennis serves with the maximum effort, and three-dimensional kinematic data of the thorax, scapula, and humerus of the dominant side were recorded by an electromagnetic tracking device (Liberty; Polhemus) at 240 Hz. The humeral rotation with respect to the thorax (named as the resultant shoulder rotation) was decomposed into the scapular rotation with respect to the thorax and the humeral rotation with respect to the scapula (named as the glenohumeral rotation). The scapular rotation that contributed to attain the peak resultant shoulder external rotation was quantitatively determined, and the ratio of the glenohumeral external rotation to the scapular rotation that contributed to attain the peak resultant shoulder external rotation was computed to represent the scapulohumeral rhythm for shoulder external rotation. RESULTS: Of the three components of scapular rotations, the scapular posterior tilt was the primary component that contributed to the attainment of the peak resultant shoulder external rotation. The scapulohumeral rhythm for shoulder external rotation (scapular posterior tilt-glenohumeral external rotation) exhibited during the backswing phase was 1:2.3. CONCLUSIONS: The peak resultant shoulder external rotation was generated by a synchronized combination of the scapular posterior tilt and glenohumeral external rotation. A consistent pattern of three phases of the scapular posterior tilt and the glenohumeral external rotation that could be accurately modeled by three linear regressions was observed in preparation for the peak shoulder external rotation in tennis serve. © 2010 by the American College of Sports Medicine.

ISSN：03601323

Outline：The environment of workplace in an office involved in creative work was evaluated in 2005 and 2006. The M Company has installed partition based task/ambient conditioning systems (TAC) and several environment-friendly systems, such as double-skin and thermal-storage structures. It was intended to investigate the influence of the worker's behavior and task conditioning on worker's thermal comfort and productivity. In this survey, immediate thermal environment and worker's behavior were measured, and occupants' surveys of thermal comfort and feeling of fatigue were conducted. We found that both activity level of occupant and exposed thermal environment is greatly different one by one. It is suggested that an increase in metabolic rate according to worker's behavior influenced on their thermal comfort. Based on the knowledge obtained from this investigation, needs for TAC are discussed. © 2009 Elsevier Ltd. All rights reserved.

ISSN：0021-9290

ISSN：0195-9131

Outline：

The present study aimed to introduce a new index of muscle cross-sectional area (CSA) and to examine the relationship between the muscle CSA index determined during isometric maximal voluntary contraction (MVC) and muscle strength. As a result of the quantification of cross-sections of elbow flexor muscles at rest and during a low-intensity contraction using magnetic resonance imaging (MRI), the product of muscle thickness and circumference of a limb (MT×C) was shown to be appropriate to assess muscle CSA. In young adults, MT×C during MVC is similarly or more closely related to muscle strength than that at rest. On the other hand, in middle-aged and elderly individuals, MT×C during MVC is more closely related to muscle strength than that at rest. Thus, the age-related difference in the relationship between MT×C and muscle strength was found. Muscle deformation induced by MVC for middle-aged and elderly men is suggested to be greater than that for young men, and it would have affected the above age-related discrepancy. The present findings indicate that MT×C during isometric MVC is able to more accurately examine one's ability to exert force than that at rest.

Outline：The purpose of this study was to examine the factors influencing the behavior of the baseball during and after the impact with a wooden bat. A finite element approach was used to model the behavior of a baseball and a wooden bat at the impact and the linear and angular velocities of the ball after the impact were determined for given sets of impact condition. The simulation outcome was validated with 23 sets of actual measurements taken during a "free batting practice" performed by the members of a collegiate baseball team. The simulation results demonstrated high level of matching with the experimentally measured values.

Outline：The purpose of this study was to characterize the bat swing parameters that increase the flight distance. Thirteen members of a collegiate baseball team performed free-batting practice. The batting performances were recorded with a ultra-high-speed camera and a tri-axial gyro-sensor attached to the grip end of a wooden baseball bat. Flight distance had a high correlation with the kinetic energy possessed by the batted ball (p<0.01) which, in turn, was correlated with the rolling velocity of the bat (p<0.05), the direction of the bat swing (p<0.01) immediately before the impact (p<0.05) and the orientation of the line of impact (p<0.05).

Outline：Task/ambient conditioning systems (TAC) are being investigated and are effective air conditioning methods for offices, which can keep steady temperatures, efficiently remove thermal loads, and create a comfortable environment that is pleasant for users. In this study, subjective experiments with a task conditioning system were conducted to investigate thermal comfort and productivity by field measurements. Air change effectiveness of the system was also evaluated using SF6 tracer gas.

ISSN：0268-0033