The purpose of this study was to investigate kinematic factors to pitch fast ball by comparing motions of two groups of baseball pitchers whose ball velocities were significantly different. Twenty-two baseball pitchers participated in this study as subjects. Their pitching motion was videotaped with two high-speed video cameras to compare three dimensional kinematics. Subjects were divided into two groups, i.e., high and low ball velocity groups (HG and LG). Average ball velocity of the HG was significantly larger than that of the LG (HG, 35.7±1.0 m/s, n=10; LG, 33.2±1.1 m/s, n=12; p<0.001). From the instant of the maximal knee height of the stride knee to the middle of the second phase (from the instant of the minimum height of the throwing hand to the instant of the stride foot contact), the HG flexed the knee and hip of the pivot leg and inclined the thigh backward more than the LG. At the stride foot contact (SFC), the HG flexed the knee of the stride leg and rotated the lower trunk more than the LG. In the first half of the third phase (from SFC to the ball release), the elbow joint angle of the throwing arm of the HG was kept about 80 degrees while it was about 60 degrees for LG. The timing of the peak angular velocity of the horizontal adduction of the shoulder of the HG was significantly later than that of LG, but the angular velocity was larger in the magnitude because of longer range of motion of the horizontal adduction in HG.
