著者

Koji MUROFUSHI Shinji Sakurai Koji Umegaki Kazutoshi Kobayashi

出版者

Japan Society of Physical Education, Health and Sport Sciences

雑誌

International Journal of Sport and Health Science (ISSN:13481509)

巻号頁・発行日

vol.3, pp.116-128, 2005 (Released:2008-01-23)

参考文献数

18

被引用文献数

13 17

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The aim of this study was to compare the radius of curvature and the estimated head speed as measured by sensors attached to a hammer with those calculated by video image analysis. The participant was the Japanese record holder(83m47). He threw a hammer with sensors which measured the force exerted along the length of the hammer cable using a tension meter made of a metal plate to which strain gauges were affixed, and the angular velocity perpendicular to the hammer cable using two IC accelerometers whose axes were aligned together with the hammer cable. The radius and speed obtained using the sensors were similar to those obtained from video analysis in values, but were slightly out of phase. This is because measuring the angular velocity by sensors eliminates translational motion and only produces results for rotational motion. The length of time required to obtain these results was shortened by the use of a hammer with sensors. Therefore, the system using sensors attached to a hammer will enable athletes and coaches to interpret the data about each throw while it is still fresh in their minds.

著者

Gen Horiuchi Shinji Sakurai

出版者

Japan Society of Physical Education, Health and Sport Sciences

雑誌

International Journal of Sport and Health Science (ISSN:13481509)

巻号頁・発行日

vol.14, pp.94-101, 2016 (Released:2017-03-17)

参考文献数

19

被引用文献数

4 6

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The purpose of this study was to identify mechanisms to increase bat head speed in baseball batting, from the view-point of kinetics. The batting motion of ninety-nine amateur baseball players was recorded with a motion capture system, and the kinematics and kinetics of the bat were analyzed. The bat's rotational power increased with the torque exerted on the bat's grip. However, torque and rotational power declined just prior to impact. It can be interpreted that these declines arise from a decrease in torque exerted by the wrist's periarticular muscles as the bat's rotational velocity increases (muscle force-velocity relationship). On the contrary, the bat's translational power increased just prior to impact. Judging from the relationship between the force exerted on the bat's grip in the direction of the bat's long axis and the bat head speed, the bat's translational power seems to depend on the bat's grip velocity in the direction of the bat's long axis. It was revealed that the bat's energy, by the application of rotational and translational power at different times, contributes to an increase in bat head speed in baseball batting.

著者

神事 努 桜井 伸二 清水 卓也 鈴木 康博 Tsutomu JINJI Shinji SAKURAI Takuya SHIMIZU Yasuhiro SUZUKI

雑誌

中京大学体育学論叢 = Research journal of physical education Chukyo University (ISSN:02887339)

巻号頁・発行日

vol.49, no.1, pp.21-27, 2008-01-01

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It has been reported that the spin axis of a pitched baseball differs between adult pitchers and youth pitchers (Tezuka and Himeno 2001). However, that information was based on visual observation, and has not been determined quantitatively. The purpose of this study was to investigate the ball spin orientation and spin rate of youth pitchers compared with those for adult pitchers. In addition, the development of the throwing motion and factors in the determination of spin rate were discussed. Fourteen youth baseball pitchers (13.9±1.2 years) and nine collegiate baseball pitchers (20.1± 0.8 years) were selected as subjects. All of them were classified as over-hand style pitchers. The baseball was filmed immediately after the ball release using a high-speed video camera (250 Hz). The direction of spin axis and the spin rate were calculated using positional changes of drawn marks on the ball surface. The direction of the spin axis was defined by two angles, θ(azimuth) and φ(elevation). The angle between spin axis and pitching direction (α) was also obtained (Jinji and Sakurai 2006). Mean values of the angles of the spin axis showed no significant differences between youth pitchers and collegiate pitchers. As for variations within each trial, however, youth pitchers were significantly more inconsistent than collegiate pitchers. Although youth pitchers have acquired similar pitching motion to adults on average, their motion was often unstable with large variations. There was a significant difference in the mean values of spin rate between the youth pitchers and collegiate pitchers (p<0.001). Moreover, the spin rate correlated significantly with the initial ball velocity (p<0.001). Pitchers with a higher initial velocity achieved a notably higher spin rate. It was concluded that a pitching motion that increased the ball velocity consequently increased spin rate.

著者

Ryoji Toyoshima Shinji Sakurai

出版者

Japan Society of Physical Education, Health and Sport Sciences

雑誌

International Journal of Sport and Health Science (ISSN:13481509)

巻号頁・発行日

vol.14, pp.41-50, 2016 (Released:2016-09-30)

参考文献数

26

被引用文献数

6

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The present study aimed to clarify kinematics among sprinters with similar step length but different step frequencies, and with similar step frequencies but different step lengths in sprinting. We collected kinematic data from 54 sprinters at approximately the 60 m point of a 100-m sprint using a high-speed camera. The sprinters within 0.5SD from the mean value of each of step frequency and length at top speed phase were included in the ‘SL-similar’ (n=22, step frequency: 3.99-5.19 Hz, step length: 2.07-2.15 m) and the ‘SF-similar’ (n=22, step frequency: 4.51-4.72 Hz, step length: 1.93-2.33 m) groups, respectively. In the SL-similar group, higher step frequency was correlated with shorter stance time (r=−0.899), and a more vertical thigh angle at take-off (r=0.623). In the SF-similar group, longer step length was correlated with greater distance of the hip during flight phase (r=0.847), and a larger vertical acceleration of the forward swinging leg relative to the hip (r=0.438). In conclusion, leg kinematics at touchdown and take-off are important for high step frequency in similar step length, and forward swinging leg kinematics are important for long step length in similar step frequency.