Technical noteShoulder joint movement of the non-throwing arm during baseball pitch—comparison between skilled and unskilled pitchers
Introduction
Less kinematic differences are desirable to attain an effective pitch (Barrentine et al., 1998; Escamilla et al., 1998). For several phases of throwing (stride foot contact, arm cocking, arm acceleration, and ball release), Fleisig et al. (1999) found kinematic and kinetic parameters of baseball pitching that reached statistically significant differences among competition levels and suggested that they might be used to learn proper pitching mechanics and protect a pitcher from potential injuries. The shoulder of the non-throwing arm stayed in an almost steady position while the shoulder on the throwing arm moved in a nearly circular path around it (Feltner, 1989). This observation shows that the shoulder of a non-throwing arm is important as a pivot or fulcrum of the trunk or throwing arm to rotate about.
On the basis of this observation, the movement of the shoulder joint of the non-throwing arm may be important to attain a skilled pitch and higher initial ball velocity. However, the observation has not been demonstrated quantitatively. We know of no studies that report on the kinematics of the shoulder of the non-throwing arm, compare it between skilled and unskilled pitchers, and relate it with initial ball velocity. The purpose of this study was to verify the hypothesis that a pitcher with less movement (displacement) of the shoulder of the non-throwing arm can attain higher ball velocities. We also attempted to examine whether the shoulder-joint movement (SJM) of the non-throwing arm was less for the skilled than for the unskilled pitchers.
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Methods
Six baseball pitchers playing for a business corporation and three high-school baseball pitchers, ranging in age from 18 to 25 were used as subjects (Table 1). Their mean height (±S.D.) and mean weight (±S.D.) were 175.6±8.9 cm and 72.5±10.3 kg, respectively. They were all in good health and did not have injuries. They were not recovering from an injury either, and they had not undergone surgery in the recent past. Each subject had at least three years’ experience throwing two types of pitches
Results
The mean initial ball velocity of fastball pitches for the skilled group was faster than that for the unskilled group (Table 2). The mean initial ball velocity of curveball pitches did not differ between the skilled and unskilled group (Table 2). These data validate the classification of all subjects into the skilled and unskilled groups. The mean SJM, SJMx, and SMJy tended to be higher for the unskilled pitchers than for the skilled pitchers (Table 3). It was verified that the movement of the
Discussion
A larger torque produces faster motion of the throwing arm and consequently leads to faster initial ball velocity (Feltner and Dapena, 1986). The shoulder of the non-throwing arm was in a roughly constant position while the shoulder of the throwing arm moved in a nearly circular path around it (Feltner, 1989). The shoulder of the non-throwing arm acts as a pivot point or fulcrum for the upper trunk and throwing arm to rotate about. Therefore, the role of the shoulder of the non-throwing arm may
Acknowledgements
The author would like to thank Hirokazu IWASE for his assistance.
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