The aim of this study was to determine the contribution of the upper trunk rotation consisting of roll-pitch-yaw to hand velocity in the forwards-backwards direction during front crawl strokes and to investigate the association of forwards-backwards hand velocity induced by the upper trunk rotation with stroke frequencies. Fifteen skilled swimmers with retro-reflective markers performed front crawl strokes in a swimming pool where a motion capture system was set. Forwards-backwards hand velocity solely induced by the upper trunk rotation was determined during the performance. In the pull and push phases, 28% and 19% of the backward hand velocity was induced by the upper trunk rotation, respectively, while 19% of the forward hand velocity resulted from the upper trunk rotation in the recovery phase. The upper trunk rotation contributed to the forwards-backwards velocity as much as the elbow joint and was the second primary source of backward hand velocity in the pull phase. The forwards-backwards hand velocity created by the upper trunk rotation was associated with the stroke frequencies (r = 0.56, p < 0.05). The forwards-backwards hand velocity induced by the upper trunk would influence hand propulsion and stroke frequency so that a swimmer and coach should consider this performance-enhancing variable.

This technical report introduces a method for measuring the three-dimensional articular motions of the shoulder complex during swimming. Eleven collegiate swimmers performed front-crawl strokes at maximal effort and their shoulder motions were measured with an electromagnetic tracking device. Sensors were attached to the sternum, acromia and humeri to determine their relative positions and orientations. A cart carrying the components of the device was pushed back-and-forth along the poolside, so that the sensors attached to the swimmer could be detected within the electromagnetic field. The stroke-to-stroke reliability of the measured articular motions was determined for each swimmer. The accuracy of the device was tested by measuring the relative positions and orientations of multiple sensors fixed on a wooden stick moving above and below the water surface. The measured values were compared with pre-determined fixed values. The coefficient of variance for the joint angles between stroke cycles was <10% of the total range of movement. Within a range of 1282 mm from the transmitter, the root-mean-square error of measurement was 0.7° for orientation and 4 mm for position, both of which were superior to optical measurements. This method is accurate and reliable for measuring the kinematics of the shoulder complex during swimming.

The study aims to test three hypotheses: (a) the rotation of the upper trunk consists of roll, pitch and yaw of frequencies harmonic to the stroke frequency of the front crawl stroke, (b) the rotation of the upper trunk generates back-and-forth movements of the shoulders, which enhances the movements of the stroking arms, and (c) the angular velocities of roll, pitch and yaw are associated with hand propulsion (HP). Front crawl strokes performed by twenty male swimmers were measured with a motion capture system. The roll, pitch and yaw angles about the three orthogonal axes embedded in the upper trunk were determined as three sequential Cardan angles and their angular velocities were determined as the three respective components of the angular velocity. HP and the drag and lift components of HP (HP and HP ) were estimated by the hand positions and the data from twelve pressure sensors attached on hands. The roll, pitch, and yaw angles were altered in frequencies harmonic to the stroke frequency during the front crawl stroke. Shoulders alternately moved back and forth due to the upper trunk rotation. In the pull phase the angular velocity of roll was correlated with HP (r = −0.62, p = 0.004). Based on the back-and-forth movements of the shoulders and roll motion relative to a hand movement, the arm-stroke technique of the front crawl swimming was discussed in terms of increasing the hand velocity and HP. D L L

The aims were to quantitatively describe the coordinated motions of the scapula and humerus during fully tethered front-crawl strokes and to test the hypothesis that scapular motion functions to reduce the risk of subacromial compression. An electromagnetic tracking device was used to record the kinematics of the thorax, humerus, and scapula on the dominant side in 17 collegiate swimmers. Because evidence suggests that compressive force develops under the coracoacromial arch when the arm elevated above 90º of arm elevation is maximally internally rotated, such shoulder configurations were measured for each participant. A series of scapulohumeral angles measured with this procedure were compared with the corresponding angles exhibited during fully tethered front-crawl swimming to identify the scapulohumeral angles indicative of subacromial compression. Additional comparison was performed without taking the scapular motion into account. Scapulohumeral angles indicative of subacromial compression were observed in 15 participants, accounting for 7.7 ± 7.1% of stroke cycle time. This duration was significantly less than the corresponding duration identified without having taken the scapular motion into account (22.6 ± 13.8% of stroke cycle time). The difference was due primarily to the unique movements of the scapular to accommodate demands imposed by stroke motions, and this supported the hypothesis.

The purpose of this study was two-fold; to determine the optimum impact condition for maximizing flight distance toward the opposite field and to examine the influence of the bat angles at impact on the batted ball characteristics (speed, rotation, and angle immediately after impact) and the flight characteristics (distance, trajectory, and time). Various impact conditions were defined using 3 factors: the angles of the bat at impact projected to the horizontal and vertical planes, and the vertical inclination angle of the line of impact (the product of the sine of this angle and the radius of the ball determines the under-cut distance). Three-dimensional finite element analysis was used to construct a model of impact between a baseball and a wooden baseball bat and to conduct simulation analysis. The initial flight condition of the batted ball after the impact was determined for each simulated condition, and the flight distance was estimated from the initial flight condition. The results showed that a nearmaximum flight distance of 90-95 m was attained over a wide range of the opposite field when the bat head was not lowered substantially more than the grip-end. However, when the bat head was lowered substantially more than the grip-end, the flight distance attainable with the given impact condition decreased as the vertical bat angle increased, and the range of horizontal bat angle within which a great flight distance was attainable became narrower. The latter results suggest that a batsman needs to acquire a sophisticated technique with a greater precision of ball impact to hit a ball toward a given horizontal angle in the opposite field if the bat swing is characterized as lowering of the bat head to a large extent.

We investigated the rotational effect of buoyant force around the body’s transverse axis, termed buoyant torque, during a 200m front crawl maximal swim. Eleven male swimmers of national or international level participated. One stroke cycle (SC) for each 50m was recorded with two above and four below water cameras. The following variables were analysed: swimming velocity; absolute and normalised buoyant force; minimum, average and maximum buoyant torque; SC and arm recovery times. The average value of buoyant torque was higher in the first 50m (14.2 ± 4.5Nm) than in the following 150m (9.3 ± 4.1Nm~10.9 ± 4.5Nm) and was directed to raise the legs and lower the head throughout the race. The change in its magnitude seemed to be linked to the shorter time spent proportionally in arm recovery (first 50m: 27.6% of SC time; next 150m: 23.3–24.4% of SC time). Most swimmers had periods of the SC where buoyant torque was directed to sink the legs, which accounted to 10% of SC time in the first 50m and about twice this duration in the next 150m. These periods were observed exclusively at some instances when the recovering arm had entered the water while the opposite arm was still underwater.

The purpose of this study was to test the validity of using a one- and a two-segment models for determining elbow joint valgus stress during baseball pitching. The one-segment model consisted of a single segment representing the ball, hand and forearm together as a rigid segment. The two-segment model consisted of a distal segment representing the ball, hand and forearm together as a rigid segment and a proximal segment representing the upper arm. In addition, a three-segment model, which is the most widely and frequently used model for determining the valgus stress of baseball pitching, was defined to provide a reference value for testing the validity of the fewer segment models. The three-segment model was comprised of a distal segment representing the ball and hand together as a rigid segment, a mid-segment representing the forearm and the proximal segment representing the upper arm. Fourteen university students with the baseball experience were asked to throw a baseball with their maximum effort and a motion capture analysis system (VICON, Oxford Metrics) was used to measure the motions of the segments. The result showed that the maximum values of the valgus stress determined with one- and two-segment models (approx. 64 Nm for fast balls) were significantly greater than the corresponding value determined with three-segment model (47 Nm), but the correlations among the three models were found to be significantly high (r > 0.83, p < 0.01). These findings suggest that the fewer segment models can be used to compare the magnitude of valgus stress among subjects and among pitches for evaluation of risk of elbow injuries.

Purpose: This study aimed to elucidate growth pattern of mechanical properties of the Achilles tendon and to examine if imbalance between growth of bone and muscle–tendon unit occurs during adolescence. Methods: Fourteen elementary school boys, 30 junior high school boys, 20 high school boys and 15 male adults participated in this study. Based on estimated age at peak height velocity (PHV), junior high school boys were separated into two groups (before or after PHV). An ultrasonography technique was used to determine the length, cross-sectional area, stiffness and Young’s modulus of Achilles tendon. In addition, the maximum strain in “toe region” (strain ) was determined to describe the balance between growth of bone and muscle–tendon unit. Results: No group difference was observed in length, cross-sectional area and strain among the groups. However, stiffness and Young’s modulus in after PHV groups were significantly higher than those of elementary school boys and before PHV groups (p ≤ 0.05). Conclusions: These results indicate that mechanical properties of Achilles tendon change dramatically at and/or around PHV to increased stiffness. The widely believed assumption that muscle–tendon unit is passively stretched due to rapid bone growth in adolescence is not supported. TP TP

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 soil filled 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 I\T-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.

In this study, we present a position estimation of ball impact in baseball batting using PVDF films. A vibration sensor consisted of two PVDF films in a cross shape was developed. The outputs from the PVDF films were normalized and filtered. We calculated the largest peak of the normalized and filtered outputs to eliminate the effect of intensity of the impact and extract a primary vibration mode, and the amplitude ratio between two outputs. The largest peak and the amplitude ratio were used as the parameters for the estimation. Fundamental experiments on the different impact intensities and the different positions showed that the largest peak well reflected the longitudinal impact position of the impact and the amplitude ratio reflected both longitudinal and circumferential impact positions of the impact. Then, we proposed an estimation method in which the longitudinal position was estimated firstly, then the circumferential position was estimated. The validation test showed that the estimation errors were small around the sweet spot, indicating that our sensor has the capability of determining the longitudinal and circumference positions of the ball impact in baseball batting.

大学生野球投手を対象とし、腱板筋群のストレッチを行なった際の投球動作における肩甲上腕リズムの縦断的変化を調べた。大学トップレベルの投手11名に肩甲骨を他動的に固定して行なう腱板筋群のストレッチを指導し、継続的に実施させた。事後測定は事前測定の85、201、287日後に行なわれ、最後まで調査を実施できた7名を分析対象とした。投球動作における肩複合体の運動は電磁ゴニオメータで計測した。最大外旋時の胸郭に対する上腕骨の外転角はほぼ一定であったが、肩甲骨に対する上腕骨の外転角が事前測定(77±9°)と比較して85日後(86±12°)、201日後(89±13°)、287日後(88±11°)で有意に増加した。これは腱板筋群のストレッチが投球動作における肩甲上腕リズムを変化させたことを示している。(著者抄録)

A wide range of topspin rotation of a bat around the long-axis, referred to as &ldquo;rolling&rdquo;, 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 &ldquo;free-batting&rdquo; 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&plusmn;376&deg;/s, comprised a negative contribution attributable to the batter's effort of exerting torque (Mechanism 1; &minus;1144&plusmn;488&deg;/s) and a positive contribution attributable to the gyroscopic effect (Mechanism 2; 1808&plusmn;339&deg;/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.<br>

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.

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.

In this study, we analyzed the kinematic characteristics of various types of baseball pitches by elite baseball pitchers, and tested a null hypothesis that &ldquo;no type of pitch has the same kinematic characteristics as another.&rdquo;<br>  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.<br>  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.<br>  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.<br>

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".

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.

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.

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.

The purpose of this study was to test the hypothesis that the passive drag acting on a gliding swimmer is reduced if the swimmer adopts an abdominal breathing manoeuvre (expanding the abdominal wall) rather than chest breathing manoeuvre (expanding the rib cage). Eleven male participants participated in this study. A specialised towing machine was used to tow each participant with tension set at various magnitudes and to record time series data of towing velocity. Participants were asked to inhale air by expanding the abdominal wall or the rib cage and to maintain the same body configuration throughout gliding. The steady-state velocity was measured and the coefficient of drag was calculated for each towing trial to compare between the breathing manoeuvres. The results showed that the towing velocity was increased by 0.02 m/s with a towing force of 34.3 N and by 0.06 m/s with a towing force of 98.1 N. The coefficient of drag was reduced by 5% with the abdominal breathing manoeuvre, which was found to be statistically significant (p < 0.05). These results indicate that adopting the abdominal breathing manoeuvre during gliding reduces the passive drag and the hypothesis was supported.

Background: The role of the scapula during high-velocity baseball pitching has been described without 3-dimensional kinematic data. It has been speculated that the scapula functions to align the humerus with the spine of the scapula on both the transverse and scapular planes at the end of the arm-cocking phase. Hypothesis: Two hypotheses were formulated: (1) the scapulothoracic protraction angle correlates with the humerothoracic horizontal adduction angle among participants, and (2) the scapulohumeral rhythm of the humerothoracic elevation is not the same as the normal ratio (2:1) observed widely in controlled abductions. Study Design: Descriptive laboratory study. Methods: A total of 20 Japanese professional baseball pitchers were asked to pitch 3 fastballs as they would normally during pitching practice. The 3-dimensional kinematic data of the thorax, scapulae, humeri, and pelvis were recorded using an electromagnetic tracking device operating at 240 Hz. Humerothoracic, scapulothoracic, and glenohumeral joint configurations were determined at the instant of stride-foot contact (SFC) and the end of the arm-cocking phase (MER). Results: The mean (±SD) glenohumeral horizontal adduction (-6° ± 7°) and elevation (85° ± 10°) angles at the MER indicated that the humerus was positioned almost parallel to the spine of the scapula. The mean scapulothoracic protraction angle (15° ± 10°) was significantly correlated with the humerothoracic horizontal adduction angle (10° ± 11°) at the MER (r = 0.76, P <.001) but not at the SFC (r = 0.13, P =.58). The scapulohumeral rhythm (4.2 [±1.9]:1) expressed as the ratio of the glenohumeral elevation angle to the scapulothoracic upward rotation angle at the MER was significantly greater than the normal ratio (2:1) (P <.01). Conclusion: The results supported the hypotheses, providing evidence to corroborate the widely accepted concept that the scapula functions to align the humerus with the spine of the scapula so as to limit the glenohumeral joint configuration within the "safe zone" at the MER. Clinical Relevance: Disruption of coordination, such as abnormal patterns including "SICK" scapula (scapular malposition, inferior medial border prominence, coracoid pain, and dyskinesis) and scapular dyskinesis, may result in an abnormal configuration of the glenohumeral joint at the MER.

The rotation of the golf-club around the long-axis of the shaft may be generated by two mechanisms. The 1^<st> mechanism is the angular impulse exerted by the golfer around the long-axis of the shaft directly. The 2^<nd> 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^<st> mechanism was 3543±378°/s in direction of "opened face", on the other hand the angular velocity attributed to 2^<nd> 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.

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 step to the 19 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 step to the 19 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 step to the 19 step and the horizontal velocity from the 7 step to the 19 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. st th th th st th th th

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.<br>

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.<br>

Inability to control lower extremity segments in the frontal and transverse planes resulting in large knee abduction angle and increased internal knee abduction impulse has been associated with patellofemoral pain (PFP). However, the influence of hip rotation angles on frontal plane knee joint kinematics and kinetics remains unclear. The purpose of this study was to explore how hip rotation angles are related to frontal plane knee joint kinematics and kinetics during running. Seventy runners participated in this study. Three-dimensional marker positions and ground reaction forces were recorded with an 8-camera motion analysis system and a force plate while subjects ran along a 25-m runway at a speed of 4. m/s. Knee abduction, hip rotation and toe-out angles, frontal plane lever arm at the knee, internal knee abduction moment and impulse, ground reaction forces and the medio-lateral distance from the ankle joint center to the center of pressure (AJC-CoP) were quantified. The findings of this study indicate that greater hip external rotation angles were associated with greater toe-out angles, longer AJC-CoP distances, smaller internal knee abduction impulses with shorter frontal plane lever arms and greater knee abduction angles. Thus, there appears to exist a conflict between kinematic and kinetic risk factors of PFP, and hip external rotation angle may be a key factor to control frontal plane knee joint kinematics and kinetics. These results may help provide an appropriate manipulation and/or intervention on running style to reduce the risk of PFP.

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."

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.

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.

The present study aimed to re-examine the influence of the isometric plantarflexors contraction on the Achilles tendon moment arm (ATMA) and the factors influencing the ATMA in three-dimensions. A series of coronal magnetic resonance images of the right ankle were recorded at foot positions of 10° of dorsiflexion, neutral position, and 10° of plantarflexion for the rest condition and the plantarflexors contraction condition at 30% maximal voluntary effort. The shortest distance between the talocrural joint axis and the line of action of the Achilles tendon force projected to the orthogonal plane of the talocrural joint axis was determined as the ATMA. The ATMA determined in the contraction condition was significantly greater by 8 mm than that determined in the rest condition. The talocrural joint axis was displaced anteriorly by 3 mm and distally by 2 mm due to the muscle contraction. As the same time, the line of action of the Achilles tendon force was displaced posteriorly by 5 mm and medially by 2 mm. These linear displacements of the talocrural joint axis and the line of action of the Achilles tendon force accounted for the difference in the ATMAs between the two conditions by 35.9 and 62.4%, respectively. These angular displacements accounted for the total of 0.4% increase in the ATMA. These results confirm the previous findings reported in two-dimensional studies and found that the linear displacement of the line of action of the Achilles tendon force is the primary source of the contraction-induced increase in the ATMA.

健康な成人男性8名(身長1.69±0.04m、体重62.8±6.5kg、25±2歳)を対象に、ヒト生体腱におけるつま先領域と線形領域を正確にモデル化し、境界点における腱伸張および腱張力の値を推定する方法を提案した。maximal voluntary contraction(MVC)は日間で有意差が認められず、変動係数(CV)は3.1±1.5%であった。境界点における腱伸張は日間で有意差が認められず、CVは3.9±3.2%であった。境界点における腱張力は日間で有意差が認められず、CVは7.7±3.7%であった。ΔX nの算出区間を変えた場合の境界点における腱伸張および腱張力の値はそれぞれ10.1±2.1mm(1日目)、10.2±2.2mm(2日目)、1348.7±437.5Nm(1日目)、1300.0±483.4Nm(2日目)であった。いずれの値も10%MVCごとに算出した場合と有意な差は認めなかった。

We aimed to examine whether the influence of conditioning contraction intensity on the extent of postactivation potentiation (PAP) is muscle dependent. Eleven healthy males performed both thumb adduction and plantar flexion as a conditioning contraction. The conditioning contraction intensities were set at 20%, 40%, 60%, 80%, or 100% of the maximal voluntary isometric contraction (MVC).Before and after the conditioning contraction, twitch torque was measured for the respective joint to calculate the extent of PAP. In plantar flexion, the extent of PAP became significantly larger as the conditioning contraction intensity increased up to 80% MVC (p<0.05). In contrast, the extent of PAP in thumb adduction increased significantly only up to 60% MVC (p<0.05), but not at higher intensities.These results indicate that the influence of the conditioning contraction intensity on the extent of PAP is muscle dependent. Our results suggest that a conditioning contraction with submaximal intensity can sufficiently evoke sizable PAP in the muscle where most of muscle fibers are recruited at submaximal intensities, thereby attenuating muscle fatigue induced by the conditioning contraction. © 2014 Elsevier Ltd.

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.

The knee is the most common site of running injuries, particularly prevalent in females. The purpose of this study was to clarify gender differences in the lower extremity kinematics during running, with a specific emphasis on the relationships between the distal and proximal factors and the knee joint kinematics. Eleven female and 11 male runners participated in this study. Three-dimensional marker positions were recorded with a motion analysis system while the subjects ran along a 25 m runway at a speed of 3.5 m/s. Kinematic variables were analyzed for the stance phase of the right leg. Female runners demonstrated significantly greater peak knee abduction (P<0.05), hip adduction (P<0.01) and internal rotation (P<0.05), whereas male runners demonstrated significantly greater peak rearfoot eversion (P<0.01). The knee abduction angles were positively correlated with hip adduction angles (r=0.49, P<0.05) and negatively correlated with rearfoot eversion (r= -0.69, P<0.001). There was no significant difference in normalised step width between genders (P>0.05). Smaller rearfoot eversion and greater hip adduction related closely to the greater knee abduction as the distal and proximal factors, respectively. These relationships are thought to be the compensatory joint motions in the frontal plane, because there was no significant difference in the normalised step width between females and males. The current results suggest that if the step width is identical, the subjects with greater knee abduction had smaller rearfoot eversion to compensate for greater hip adduction, which were more apparent in females. This explains greater knee abduction found in female runners, which can be linked to a high risk of knee injury. © 2014 Copyright European College of Sport Science.

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.

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.

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.

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.

The purpose of this study was to examine the relationship between muscle architecture of the triceps brachii (TB) and joint performance during concentric elbow extensions. Twenty-two men performed maximal isometric and concentric elbow extensions against various loads. Joint torque and angular velocity during concentric contractions were measured, and joint power was calculated. Muscle length, cross-sectional areas, and volume of TB were measured from magnetic resonance images. Pennation angle (PA) of TB at rest was determined by ultrasonography. The PA was significantly correlated with the maximal isometric torque (r = .471), but not to the torque normalized by muscle volume (r = .312). A significant correlation was found between PA and the angular velocity at 0 kg load (r = .563), even when the angular velocity was normalized by the muscle length (r = .536). The PA was significantly correlated with the maximal joint power (r = .519), but not with the power normalized by muscle volume (r = .393). These results suggest that PA has a positive influence on the muscle shortening velocity during an unloaded movement, but does not have a significant influence on the maximum power generation in untrained men. © 2013 Human Kinetics, Inc.

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 , 6.1 ± 2.0 %) and adults (180 ± 30 mm, 63 ± 7 mm , 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. 2 2

Not only twitch torque but also the maximal voluntary concentric torque increases after a high-intensity contraction (conditioning contraction). The purpose of this study was to test the hypothesis that the increase in the maximal voluntary concentric torque induced by a conditioning contraction is prominent when tested at fast angular velocities conditions. Twelve healthy male participants performed the maximal voluntary isometric plantar flexion for six seconds as a conditioning contraction. Before and after the conditioning contraction, peak torques during the maximal voluntary concentric plantar flexions were measured at 30°/s (slow) and 180°/s (fast), each of which was carried out in a separate condition. Isometric twitch torque was also recorded before and after the conditioning contraction in each of the two velocity conditions to confirm the extent of the positive effect of the conditioning contraction. The extent of increase in isometric twitch torque was similar between the two velocity conditions, whereas the maximal voluntary concentric torque increased significantly only in the fast velocity condition (p = 0.003). These results support the hypothesis and indicate that the maximal voluntary concentric torque can be potentiated by the conditioning contraction if the joint angular velocity during the maximal voluntary concentric contraction is sufficiently high. © 2013 Fukutani et al.

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 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.

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.<br>

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%).

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.

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. © 2012 by the American College of Sports Medicine.

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 = 12 men) 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 degrees/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 (RMSEMG) were calculated. The isometric twitch torque increased significantly after conditioning contraction at all intensities (P &lt; 0.05), whereas maximal voluntary concentric torque increased significantly only at 80% and 100% MVIC conditions (P &lt; 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. (c) 2012 Elsevier Ltd. All rights reserved.

The purpose of this study was to examine if the regional difference in muscle hypertrophy after chronic resistance training is associated with muscle activation after one session of resistance exercise. Twelve men performed one session of resistance exercise of elbow extensors. Before and immediately after the exercise, transverse relaxation time (T2)-weighted magnetic resonance (MR) images of upper arm were recorded to evaluate the muscle activation along its length. In the MR images, T2 for the pixels within the triceps brachii muscle was quantified. The number of pixels with T2 greater than the threshold (mean + 1SD of T2 before the exercise) was expressed as the ratio to the number of pixels occupied by the muscle (%activated area). Another 12 subjects completed 12 weeks of training intervention (3 days per week), which consisted of the same program variables as used in the experiment for the T2 measurement. The cross-sectional areas of the triceps brachii before and after the training intervention were measured from MR images of upper arm. The %activated area of the triceps brachii induced by one session of the exercise was found to be significantly lower in the distal region than the middle and proximal regions. Similarly, the relative increase in muscle cross-sectional area after the 12 weeks of training intervention was significantly less in the distal region than the middle and proximal regions. The results suggest that the regional difference in muscle hypertrophy after chronic resistance training is attributable to the regional difference in muscle activation during the exercise.

The present study investigated the effect of movement frequencies on the behavior of fascicles and tendons of synergistic muscles. Seven male subjects performed ankle bending (calf-raise) exercises at four movement frequencies (1.33, 1.67, 1.84, and 2.00 Hz), performed with an identical range of ankle joint motion. The fascicle and tendon behavior of medial gastrocnemius (MG) and soleus (SOL) was measured by ultrasonography while kinematic and kinetic parameters of the ankle were recorded. The torque of ankle joint was larger at higher exercise frequencies. The length change of muscle decreased and that of tendon increased at higher frequencies both for MG and for SOL, with no significant inter-muscle differences in the relative changes of muscle or tendon lengths to that of MTU. Changes of pennation angles and electromyographic activities as a function of movement frequency were also comparable for MG and SOL. These results suggest that under a stretch-shortening cycle action, the muscle-tendon interaction is altered by the movement frequency toward greater use of tendon elastic energy to provide greater MTU power at a higher frequency. Results also suggest that the movement frequency dependence of fascicle and tendon behavior is comparable between MG and SOL.

The purpose of this study was to determine in vivo moment arm lengths (MAs) of three elbow flexors at rest and during low- and relatively high-intensity contractions, and to examine the contraction intensity dependence of MAs at different joint positions. At 50 degrees,80 degrees and 110 degrees of elbow flexion, MAs of the biceps brachii, brachialis and brachioradialis were measured in 10 young men using sagittal images of the right arm obtained by magnetic resonance imaging, at rest and during 20% and 60% of isometric maximal voluntary elbow flexion. In most conditions, MAs increased with isometric contractions, which is presumably due to the contraction-induced thickening of the muscles. This phenomenon was especially evident in the flexed elbow positions. The influence of the contraction intensities on the increases in MAs varied across the muscles. These results suggest that in vivo measurements of each elbow flexor MA during contractions are essential to properly examine the effects on the interrelationships between elbow flexion torque and individual muscle forces.

Introduction: In this study we aimed to compare the extent of twitch potentiation (TP) after voluntary contraction and percutaneous electrical stimulation of muscles (neuromuscular electrical stimulation: NMES) with various stimulation frequencies at equivalent target levels. Methods: Isometric knee extensions of 10 s were performed at a 40% maximal voluntary contraction level by voluntary or NMES conditioning contractions at 20, 40, and 80 HZ of the quadriceps femoris muscle. Twitch responses were elicited by stimulating the femoral nerve transcutaneously at supramaximal intensity. Results: NMES at 80 HZ induced significantly less TP (128.7 +/- 17.1%) than voluntary contraction (156.2 +/- 23.1%), whereas no statistical difference was found in TP among voluntary and 20- and 40-HZ NMES conditioning contractions (170.8 +/- 21.1% and 162.7 +/- 16.9% for 20- and 40-HZ NMES, respectively). Conclusion: Stimulation frequency of NMES determines whether NMES can induce TP comparable to that after voluntary contraction. Muscle Nerve 45: 110115, 2012

Two-dimensional methods have been applied to determine the Achilles tendon moment arm in previous studies, although the talocrural joint rotates in three-dimension. The purpose of this study was to develop a method for determining the Achilles tendon moment arm in three-dimensions (3DMA). A series of sagittal ankle images were obtained at ankle positions of -20 degrees, -10 degrees (dorsiflexed position), 0 degrees (neutral position), +10 degrees, +20 degrees, and +30 degrees (plantarflexed position). The talocrural joint axis was determined as the finite helical axis of the ankle joint over 20 degrees of displacement, and the 3DMA was determined as the shortest distance from the talocrural joint axis to the line of action of the Achilles tendon force. The corresponding 2DMA was determined with the center of rotation method using the images captured on the sagittal plane passing through the mid-point of the medio-lateral width of the tibia. The 3DMA ranged from 35 to 41 mm across various ankle positions and was, on average, 11 mm smaller than 2DMA. The difference between the two measures was attributable primarily to the deviations of the talocrural joint axis from the anatomical medio-lateral direction. The deviations on the coronal plane (21.4 +/- 20.7 degrees) and on the transverse planes (14.8 +/- 22.6 degrees) accounted for the errors of 1.3 mm and 3.0 mm, respectively. In addition, selecting either a medially or laterally misaligned sagittal-plane image for determining the 2DMA gave rise to error by 3.5 mm. The remaining difference was accounted for by the random measurement error. (C) 2011 Elsevier Ltd. All rights reserved.

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.

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.

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.

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.

The purpose of this study was to clarify how foot deformation affects the relationship between triceps surae muscle-tendon unit (MTU) length and ankle joint angle. For six women and six men a series of sagittal magnetic resonance (MR) images of the right foot were taken, and changes in MTU length (the displacement of the calcaneal tuberosity), foot arch angle, and ankle joint angle were measured. In the passive session, each subject&apos;s ankle joint was secured at 10 degrees dorsiflexed position, neutral position (NP), and 10 degrees and 20 degrees plantar flexed positions while MR images were acquired. In the active session, each subject was requested to perform submaximal isometric plantar flexions (30%, 60%, and 80% of voluntary maximum) at NP. The changes in MTU length in each trial were estimated by two different formulae reported previously. The changes of the measured MTU length as a function of ankle joint angles observed in all trials of the active session were significantly (p &lt; 0.05) larger than corresponding values in the passive session and by the estimation formulae. In the passive session. MTU length changes were significantly smaller than the estimated values when the ankle was plantar flexed. The foot arch angle increased as the contraction level increased from rest (117 +/- 4 degrees) to 80% (125 +/- 3 degrees), and decreased as the ankle was positioned further into plantar flexion in the passive session (115 +/- 3 degrees). These results indicate that foot deformation profoundly affects the triceps surae MTU length-ankle joint angle relationship during plantar flexion. (C) 2011 Elsevier Ltd. All rights reserved.

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 similar to 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. (Jpn. J. Phys. Fitness Sports Med., 60 (4) : 453 similar to 462 (2011))

The purpose of the present study was to examine the effects of wearing a graduated elastic compression (EC) stocking, with different pressure profiles during a fatiguing calf-raise exercise session, on the torque generating capacity after exercise. Fourteen subjects performed 15 sets of 10 repetitions of calf-raise exercise, wearing one of three stockings of different compression pressure profiles: two kinds of EC stockings (one (EC30) with 30 mm Hg at the ankle, 21-25 mm Hg at the calf, and 10 mm Hg below the knee, and the other (EC18) with 18, 12-14, and 7 mm Hg at the same regions, respectively) and a non-EC sport stocking as a control (CON). Before and after the exercise, torque and electromyographic (EMG) signals of medial gastrocnemius and soleus muscles were recorded during an evoked triplet contraction and the maximal voluntary contraction (MVC). All stockings had no effect on the decline of the MVC torque whereas the reduction of the evoke triplet torque in EC30 stocking condition was significantly smaller compared with that in CON (-6.4 +/- 8.5% for EC30 and -16.5 +/- 9.0% for CON, P &lt; 0.05). The reduction of the mean power frequency of EMG during MVC in the EC30 condition was significantly smaller than that in CON (-4.4 +/- 10.9 Hz for EC30 and -18.7 +/- 7.9 Hz for CON, P &lt; 0.05). These results suggest that the EC stocking with adequate pressure at the calf region relieves muscle fatigue of the triceps surae induced by calf-raise exercise. (C) 2010 Elsevier Ltd. All rights reserved.

: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.

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.

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.

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.<br>

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 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.

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.

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.

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.

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.

KONDA, S., T. YANAI, and S. SAKURAI. Scapular Rotation to Attain the Peak Shoulder External Rotation in Tennis Serve. Med. Sci. Sports Exerc., Vol. 42, No. 9, pp. 1745-1753, 2010. 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.

This study aimed to investigate whether fatigue-induced changes in synergistic muscle forces match their tendon elongation. The medial gastrocnemius muscle (MG) was fatigued by repeated electrical stimulation (1 min x 5 times: interval 30 s, intensity: 20-30% of maximal voluntary plantar flexion torque) applied at the muscle belly under a partial occlusion of blood vessels. Before and after the MG fatigue task, ramp isometric contractions were performed voluntarily, during which tendon elongations were determined by ultrasonography, along with recordings of the surface EMG activities of MG, the soleus (SOL) and the lateral gastrocnemius (LG) muscles. The tendon elongation of MG and SOL in post-fatigue ramp was similar, although evoked MG forces dropped nearly to zero. In addition, for a given torque output, the tendon elongation of SOL significantly decreased while that of LG did not, although the activation levels of both muscles had increased. Results suggest that the fatigue-induced changes in force of the triceps surae muscles do not match their tendon elongation. These results imply that the tendons of the triceps surae muscles are mechanically coupled even after selective fatigue of a single muscle. (C) 2010 Elsevier Ltd. All rights reserved.

<p>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.</p>

The swimmer's body is acted upon by time- and position-dependent fluid forces which control linear and angular motions of the swimmer's body. In this presentation, researches on the buoyancy of human body and its influence on the front-crawl swimming are reviewed, and the current approaches for quantifying the buoyancy of a swimmer are re-examined. An early study on buoyancy of human body was found in 1757. In this study, the primary question was whether or not motionless human bodies can float in water. Similar studies were conducted in early 1900's, in which the buoyancy of human body was measured as anthropometric quantities such as the buoyant force acting on the human body submerged in water, the specific gravity of the body and the apparent body weight under water. These studies revealed that (a) not all human can float motionless in fresh water, (b) in general, women are more buoyant than men, (c) the volume of air in body cavities affects one's buoyancy, (d) buoyancy characteristics changes as children get older, and (e) the legs tend to sink from a horizontal motionless floating position. Similar approach was adopted to study if the buoyancy of a swimmer influences swimming performance. On the basis of the findings from these studies, the buoyancy was postulated to influence the swimming performances with the following mechanism: The greater the buoyancy and the lesser the leg sinking effect of buoyancy help the body to float horizontally and to reduce the immersed body cross-sectional area, both of which reduce hydrodynamic resistance, and thereby, the swimming economy would increase for better performances. In a recent study, the leg-sinking effect of buoyancy was measured as motion-dependent quantities and demonstrated that the buoyant force generated the moment that directed primarily to raise the legs and lower the head during the front-crawl swimming - the buoyancy made the leg-raising effect, rather than leg-sinking effect, during the front-crawl swimming. This counter-intuitive finding on the rotational effect of buoyancy raised a question regarding the aforementioned postulated mechanism; how the leg-sinking effect of buoyancy in a horizontal motionless floating could help the swimmer's body align horizontally during front-crawl swimming, given that the buoyancy results in the leg-raising effect on the human body during the performance of front-crawl swimming? To seek an answer for this question, the mechanism of horizontal floating of the swimmers during the front-crawl swimming needs to be re-examined in the future studies. In such studies, the buoyancy of a swimmer should not only be measured as an anthropometric quantity, but it should also be measured as a motion-dependent quantity.

The aim of this study was to develop a method to predict fluid forces acting on the human hand in unsteady flow swimming conditions. A mechanical system consisting of a pulley and chain mechanism and load cell was constructed to rotate a hand model in fluid flows. To measure the angular displacement of the hand model a potentiometer was attached to the axis of the rotation. The hand model was then fixed at various angles about the longitudinal axis of the hand model and rotated at different flow velocities in a swimming flume for 258 different trials to approximate a swimmer's stroke in unsteady flow conditions. Pressures were taken from 12 transducers embedded in the hand model at a sampling frequency of 200 Hz. The resultant fluid force acting on the hand model was then determined on the basis of the kinetic and kinematic data taken from the mechanical system at the frequency of 200 Hz. A stepwise regression analysis was applied to acquire higher order polynomial equations that predict the fluid force acting on the accelerating hand model from the 12 pressure values. The root mean square (RMS) difference between the resultant fluid force measured and that predicted from the single best-fit polynomial equation across all trials was 5 N. The method developed in the present study accurately predicted the fluid forces acting on the hand model. (C) 2007 Elsevier Ltd. All rights reserved.

Background. Subacromial impingement is a widely recognized mechanism of chronic shoulder pain. The magnitudes of the compressive forces that impinge the subacromial structures were often measured from cadaveric specimens, but it is questionable to use this data as a sole basis to determine the shoulder motions and/or shoulder configurations that induce impingement in live subjects performing active motion. The purpose of the present study was to determine in vivo the magnitude of the compressive force at selected shoulder configurations.
Methods. The subacromial structures may be impinged by the downward-directed forces exerted by the coraco-acromial ligament. The reactions of these forces push the ligament upwards and deform it into a curved shape. A single resultant of these reaction forces was determined with an inverse approach to quantify the magnitude of the impingement force. An ultrasound unit was used to visualize the deformed shape of the coraco-acromial ligament for thirteen subjects with no symptomatic shoulder problem actively holding their shoulders in five configurations.
Findings. The impingement force in 90 degrees abduction + maximum internal rotation (mean = 21.3 N) and that in the Hawkins test position (mean = 18.3 N) were significantly greater than those in 90' abduction + neutral and external rotation (means &lt;= 3 N).
Interpretation. For young asympt6matic shoulders, the motions that induce impingement are not any arm abduction, but the arm abduction with a large internal rotation. Further study is indicated to examine the impingement force among various age groups. (c) 2006 Elsevier Ltd. All rights reserved.

The purpose of this study was to test the hypothesis that, in human running at a given speed, runners select the combination of cycle rate (CR) and cycle length (CL) that minimizes the power generated by the muscles. A 2-D model of a runner consisting of a trunk and two legs was defined. A force actuator controlled the length of each leg, and a torque actuator controlled the amplitude and frequency of the backward and forward swing of each leg. The sum of the powers generated by the actuators was determined for a range of CRs at each of a series of speeds. The CR and CL vs. speed relationships selected for the model were derived from a series of CR and CL combinations that required the least power at each speed. Two constraints were imposed: the maximum amplitude of the forward and backward swing of the legs (+/-50degrees) and the minimum ground contact time needed to maintain steady-state running (0.12 sec). The CR vs. speed and CL vs. speed relationships derived on the basis of a minimum power strategy showed a pattern similar to those reported for longitudinal (within-subjects) analyses of human running. The anatomical constraint set a limit on the maximum CL attainable at a given speed, and the temporal constraint made CL decrease at high speeds. It was concluded that the process for selecting CL-CR combinations for human running has characteristics similar to the process for solving a constrained optimization problem.

Objective. To determine the suitability of a magnetic tracking device to measure pelvic bone range of motion based on palpated and digitized pelvic landmarks.
Design. A repeated measures study was conducted in two experiments to determine the reliability and validity of innominate bone range of motion measured with a magnetic tracking device in healthy subjects through passive hip abduction and external rotation.
Background. Because of the anatomical position of the pelvic joints kinematic analysis of joint motion is difficult. Accurate and precise measurements typically require highly invasive techniques involving implantation of titanium markers and exposing the subject to multiple radiographs. There is a need for a practical and accurate measurement method that will allow researchers and clinicians to accurately and reliably evaluate motion in the pelvis.
Methods. Innominate bone angles were measured for two static hip postures from the 3D spatial coordinates of the pelvic landmarks. By palpating and subsequently digitizing pelvic landmarks using an electro-magnetic tracking device the 3D coordinates were obtained. Palpated results were validated using CT scans and a metallic bead attached to the palpated landmarks.
Results. The mean range of innominate bone motion was between 3degrees and 4degrees (transverse plane) for each side with large variability across the subjects in the range of motion. Despite this variability, the measurements were found to be reliable and valid.

The purposes of this study were to quantify the rotational effect of buoyant force (buoyant torque) during the performance of front crawl and to reexamine the mechanics of horizontal alignment of the swimmers. Three-dimensional videography was used to measure the position and orientation of the body segments of 11 competitive swimmers performing front crawl stroke at a sub-maximum sprinting speed. The dimensions of each body segment were defined mathematically to match the body segment parameters (mass, density, and centroid position) reported in the literature. The buoyant force and torque were computed for every video-field (60 fields/s), assuming that the water surface followed a sine curve along the length of the swimmer. The average buoyant torque over the stroke cycle (mean = 22 N m) was directed to raise the legs and lower the head, primarily because the recovery arm and a part of the head were lifted out of the water and the center of buoyancy shifted toward the feet. This finding contradicts the prevailing speculation that buoyancy only causes the legs to sink throughout the stroke cycle. On the basis of a theoretical analysis of the results, it is postulated that the buoyant torque, and perhaps the forces generated by kicks, function to counteract the torque generated by the hydrodynamic forces acting on the hands, so as to maintain the horizontal alignment of the body in front crawl. (C) 2000 Elsevier Science Ltd. All rights reserved.

This study was conducted to describe the kinematics of bodyroll and investigate whether bodyroll was propelled primarily by the turning effect of the fluid forces (external torque) or by the reaction effect due to the acceleration of the limbs. The performances of 11 competitive swimmers were recorded using two panning periscopes, and the three-dimensional movement of the subjects was reconstructed from digitized video recordings. The external torque acting on the whole body was determined as the first time-derivative of the angular momentum of the whole body. The reaction effect of limb acceleration was determined as the first time-derivative of the angular momenta of the limbs. Shoulder roll and hip roll angles changed synchronously with the stroke frequency but their amplitudes were substantially different, indicating that the bodyroll consisted of a roll of the entire torso and a twist of the torso. The overall contribution of the external torque was to propel bodyroll, while that of the reaction effects of limb accelerations was to resist bodyroll. These results clearly indicate that the primary source for propelling bodyroll was the external torque, implications towards the mechanical interactions among bodyroll, stroke frequency, and forward propulsion in front crawl swimming were discussed.

Purpose: The purpose of this study was to determine the technical causes of shoulder impingement experienced by front-crawl swimmers. Methods: The shoulder movements exhibited during performance of the front-crawl stroke were measured using three-dimensional videography, and the instances at which each shoulder was experiencing impingement were identified. Results: On average, impingement occurred 24.8% of the stroke time (%ST). In one or more phases of the stroke cycle, each subject experienced impingement in some trials and not in other trials. This suggests that stroke technique, and not just anatomical differences, accounted for individual susceptibility to shoulder impingement. No significant difference was found between the mean values for %ST for slow and fast stroking speeds and for trials with and without hand paddles. Use of a unilateral breathing technique was often associated with a small magnitude of tilt angle (an effect of the scapular elevation/abduction on one side and depression/adduction on the other side) on the breathing side: in such cases a high incidence of shoulder impingement was observed for the shoulder on the ipsilateral side. Swimmers at high risk of experiencing shoulder impingement had three characteristics in their stroking techniques. (a) a large amount of internal rotation of the arm during the pull phase, (b) a late initiation of external rotation of the ann during the recovery phase, and (c) a small amount of tilt angle. Conclusions: A swimmer should he able to reduce the risk of developing shoulder impingement by altering the technique to eliminate the three characteristics.

Purpose: The impingement of subacromial structures has been proposed as a major cause of the shoulder problems experienced by athletes who use repetitive overhead actions. The purpose of this study was to develop a noninvasive method to identify instances at which the shoulder was experiencing impingement during front-crawl swimming. Methods: Shoulder impingement has been reported to occur when an arm is: (a) elevated above shoulder height while being rotated internally; and (b) forcibly elevated at, or beyond, the maximum active elevation angle. In this study shoulder configurations that satisfied the above two conditions were sought throughout the functional range of each shoulder; and a boundary that distinguished configurations that would cause shoulder impingement was defined. The shoulder movements exhibited during performance of the front-crawl stroke were measured using three-dimensional videography and compared with the boundary defined for each shoulder. The shoulder was considered to experience impingement if the shoulder configuration observed exceeded the boundary defined for that shoulder. Results: For a male collegiate swimmer, impingement occurred for 12% of the stroke time fur each shoulder. Conclusions: The analysis permitted the identification of the instances at which the shoulders were experiencing impingement during the front-crawl swimming. In this study, the measurement of the boundary was based entirely upon the mechanism of impingement described in the literature. Further studies are needed to confirm the occurrence of impingement by means of advanced visualization techniques, such as magnetic resonance imaging (MRI) and ultrasonogram.

The purpose of this paper is to describe a three-dimensional videography method with panning periscopes for reconstructing swimming techniques. Two panning periscope systems, developed in our laboratory, were used for the data collection. A control object (1 x 1.2 x 2) m(3) with 72 markers was placed in seven consecutive locations along the (1.5 x 8.4 x 2) m(3) calibration space. The position of the control object was recorded while panning the periscope systems, and for each of the seven locations the DLT camera parameters were determined for eight fields equally spaced through the panning motion. Each DLT camera parameter was then expressed as a function of the camera orientation by using a least-squares, second-order, polynomial regression equation, so that the DLT camera parameters for any camera orientation could be predicted (Yu et al., J. Biomechanics 26, 741-751, 1993). The three-dimensional coordinates of desired body landmarks at an instant were determined from the digitized two-dimensional coordinates for two cameras and the predicted DLT camera parameters at that instant. The accuracy of the method was evaluated by (a) the resultant errors in computing three-dimensional coordinates of precalibrated static points, and (b) the errors in computing the length of a scale rod pulled through the calibration space. The mean resultant errors ranged from 8.34 to 16.44 mm for the above- and from 9.93 to 16.22 mm for the below-water control volumes. The mean error in computing lengths on the scale rod ranged from 3.32 to 5.83 mm for three 0.5 m lengths, and 9.97 mm for a 1.5 m length. The method produced acceptable results in the reconstruction of three-dimensional motions recorded from a large space above and below the water surface.