Author(s): TANABE, G., HATASHIMA, K., AKIBA, S., TANAKA, S., Institution: KOKUSHIKAN UNIVERSITY, Country: JAPAN, Abstract-ID: 2402

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 hitting motion (1, 2, 3). In hitting motion, the step is an important movement for timing. Therefore, differences in step length are thought to affect lower limb and trunk motion. The purpose of this study was to examine that the step and kinematic characteristics of torso movement on hitting motion to the fast and slow ball velocities in soft ball players.
METHODS:
The subjects were 14 male university softball players. Batters hit fastballs (FB:26.6±2.3m/s) and slow balls (SB:20.4±0.9m/s) thrown randomly by the pitcher. Bat swing speed was measured with a swing speed measurement system (BLAST Mizuno). Hitting 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 take back (TBM) to impact (IMP), and the release (RLS), toe ground contact (TC), and heel contact (HC) times were extracted. The analysis trials were hits in the center direction both FB and SB. The analysis items were stride length, upper and lower torso rotation angles, center of gravity displacement in the direction of the pitcher.
RESULTS:
Stride length from TBM to IMP for FB and SB was significantly greater for SB than FB in TBM-TC phase and HC-IMP phase. The angles of rotation of the upper and lower torso in FB were significantly greater than that of SB in both RLS-TC phase. The distance on center of gravity toward the pitcher direction was greater SB than FB in from TBM to IMP phase, and the difference was especially significant from HC to IMP phase.　
CONCLUSION:
In this study, the kinematic characteristics of hitting motion to the fast and slow ball velocities in softball players. The response was to change the stride length and delay the timing of the upper and lower torso rotations at the time of SB hitting compared to the time of FB hitting. Also, compared to FB hitting, SB hitting may respond with a center of gravity displacement toward the direction of the pitcher during the HC-IMP phase.

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