Baseball coaches train pitchers to keep their shoulder abduction at 90º during delivery, because this angle is believed to maximize ball speed and reduce the stress on the throwing arm. In fact, however, the shoulder abduction angle for some pitchers, including professional pitchers, deviates from 90º. There likely are reasons for such deviation. The purposes of this study, therefore, were to investigate the effects of shoulder abduction angle on ball velocity and on the injury-related joint kinetic variable, and to determine why the shoulder abduction angle varies among pitchers. Eleven professional pitchers were videotaped with two high-speed cameras. The resulting kinematic data were used to simulate several pitching motions by varying the shoulder abduction angle from the actual angle. Maximum wrist velocity was used as a reasonable approximation of ball velocity. Elbow varus torque was used as a kinetic variable. The square torque for the throwing arm and torque change for the throwing arm were used to investigate the cause of the variation. It was found that the shoulder abduction angle of 90º did not always maximize wrist velocity nor minimize elbow varus torque. The actual shoulder abduction angle for each pitcher was highly consistent with the angle that minimized both square torque and torque change. The results suggested that the proficient throwers in this study moved their pitching arm so as to minimize mechanical cost while at the same time optimizing performance.

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In VRML, a modeling language for describing 3D objects on the internet, the specification to realize lifelike movement of a 3D character with a skeletal structure (such as a human) has been standardized as VRML Humanoid Animation Ver. 1 .O (H-Anim Ver. 1 .O) in the H-Anim WG of the VRML Consortium. To extend this specification, we suggest a method that makes it possible to send/receive motion data in real time on a network with narrow bandwidth such as a telephone line. Moreover, by sending the motion data with streaming data from server to client, the time required before playback can be greatly reduced. This technology uses basic techniques that can be applied widely to webbased 3D applications, broadcasting contents etc.