Kinetic analysis of individual upper limbs during baseball tee-batting motion at diŠerent hitting-point heights. Japan J. Phys. Educ. Hlth. Sport Sci. 59: 431 452, December, 2014 AbstractThe purpose of this study was to clarify the kinetic features of the upper limbs at diŠerent hitting-point heights (high, middle, and low) during baseball tee-batting. Twenty-three collegiate male baseball players (age: 19.8±1.3 yr, height: 1.74±0.04 m, weight: 74.1±6.2 kg, athletic career: 12.0± 2.1 yr) participated. Three-dimensional coordinate data were captured using a VICON MX system (12-camera, 250 Hz), and kinetic data for each hand were collected using an instrumented bat equipped with 28 strain gauges (1000 Hz). Three tee-batting heights were set for each subject based on the upper and lower limits of the strike zone according to the rules of baseball. Kinetic variables for the upper limbs, such as joint torque, joint torque power, and mechanical work, were calculated. The period of forward swing motion was divided into down-swing and level-swing phases. The results are summarized as follows: 1) The extension torque and positive torque power at each individual shoulder joint were signiˆcantly greater at the low hitting-point height than at other heights. 2) The positive torque power for extension torque at each individual elbow joint in the last half of the down-swing phase was signiˆcantly greater at the low hitting-point height than at other heights. 3) Negative power for adduction/abduction torque at each individual shoulder joint in the level-swing phase was observed at the low hitting-point height. 4) The mechanical work done by joint torque about the ‰exion/extension and adduction/abduction axes at the shoulder, the ‰exion/extension axis at the elbow, and the palmar/dorsal ‰exion and radial/ulnar ‰exion axes at the wrist showed large and positive values, and diŠered signiˆcantly among hitting-point heights. These results indicate that 1) the ‰exion/extension torque at each individual shoulder joint contributes greatly to adjustment of the translational movement of the bat in the vertical direction during the down-swing phase, 2) the adduction/abduction torque at each individual shoulder joint exerts a larger proportion of the longitudinal force of the bat to withstand centrifugal force at a low hitting-point height than at other heights in the level swing phase, and 3) consequently, it tends to be more di‹cult to adjust the bat to the hitting-point at a low height in comparison with other heights.Key wordsclosed loop problem at upper limbs, inverse dynamics calculation, instrumented bat, stationary ball batting キーワード上肢閉ループ問題，逆動力学演算，センサー・バット，静止球打撃

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

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The triggers of initial onset of yips symptoms can be broadly divided into psychological and non-psychological factors; however, a trigger-based classification of yips has not been established. This study aims to obtain insight into the prevention of yips by clarifying whether there are differences in symptoms and personality traits according to a trigger-based classification of yips in baseball players. A total of 107 college baseball players responded to a questionnaire assessing the presence or absence of yips and its symptoms. They were classified into the psychologically triggered yips group, the non-psychologically triggered yips group, and the non-yips group based on the presence or absence of yips and the triggers of its initial onset. Additionally, we compared whether personality traits examined by the NEO Five-Factor Inventory differed across these three groups. The psychologically triggered yips group had significantly higher agreeableness scores compared with the non-yips group, whereas the non-psychologically triggered yips group had significantly higher neuroticism scores compared with the psychologically triggered yips group. In the non-psychologically triggered yips group, there was a significantly higher frequency of throwing errors than in the psychologically triggered yips group, with a tendency to develop yips symptoms gradually. Since the trigger-based classification of yips is closely related to the strength of the yips symptoms and the players' personality traits, the results of this study contribute to a better understanding of the symptoms of yips and establishment of the prevention of yips. Large prospective studies are necessary to determine the causal relationship between a trigger-based classification of yips and the personality traits and symptoms of athletes with yips.