Author(s): TANABE, G., HATASHIMA, K., AKIBA, S., TANAKA, S., Institution: KOKUSHIKAN UNIVERSITY, Country: JAPAN, Abstract-ID: 767

INTRODUCTION:
Baseball and softball hitters must respond to a various pitches and velocities thrown by the pitcher. It has been there are several reports to examine the focus on timing of the baseball batting motion (1, 2, 3). In softball, the distance from the pitchers plate to home base is 14.02 m, and the hitter must respond to the ball in a short time. To clarify the characteristics of batting motions with shorter time will be useful for coaching and skill training. The purpose of this study was to examine that the kinematic characteristics of batting motion with the different ball velocity in softball players.
METHODS:
The subjects were nine male university softball players (age: 20.3±1.2yrs, height: 172.2±6.5cm, weight:68.8±9.2kg). Batters hit fastballs (FB) and slowballs (SB) thrown randomly by the pitcher. Bat swing speed was measured with a swing speed measurement system (BLAST Mizuno). Batting motions were captured using 3D motion capture system (Xsens MVN, Movella co.) and two high-speed cameras (Degimo co.). The analysis phase was from the batters takeback (TBM) to impact (IMP), and the release (RLC), toe ground contact (TOP), and heel contact (HC) times were extracted. The analysis trials were hits in the center direction both FB and SB. The analysis parameters were rotation angle of upper torso, twist range of upper and lower torso, displacement on center of gravity and velocity on the center of gravity.
RESULTS:
The pitched ball velocity by the pitchers were 26.8±2.8m/sec in FB and 19.9±0.6m/sec in SB. There was a significant difference of motion time during HC and IMP. Significant differences of relative time were also found in the TOP phase. No significant difference of bat swing speed was showed both FB and SB. The rotation angle of upper torso during TBM to IMP in FB was observed significantly greater than that of SB. On the other hand, significant difference was not observed twist range of upper and lower torso. Furthermore, displacement of the center of gravity showed greater values SB than FB. The velocity of the center of gravity in SB was higher than that of FB in HC.
CONCLUSION:
In this study, the characteristics of the batting motion for different pitched ball velocities were observed at HC and IMP phase, with significant differences at TOP phase for normalized time. In addition, it was found that the motion was characterized by a greater displacement of the center of gravity in SB. This trend was similar to baseball batting (2). From these results, it was suggested that the softball batting motion may be correspond to different ball velocity during TOP to HC phase, depending on the rotation of the upper torso and displacement of the center of gravity.

REFERENCES:
1) Ae, Human Movement Science, 2018
2) Katsumata, Human Movement Science, 2007
3) Nasu, NTT Technical Review, 2018