The present study measured isometric muscular strength and mean power elicited by trunk twisting and trunk rotation during pitching in 28 university baseball pitchers aged 18-22 years. Based on the correlations among these measurements, the purpose of the study was to clarify 1) the influence of ball velocity on isometric muscular strength, trunk power output during the stretch-shortening cycle (SSC) and trunk rotation during pitching and 2) the influence of augmentation which is an index of SSC elicited by trunk rotation on trunk rotation during pitching. We also determined mean power and augmentation during concentric (CT) and SSC rebound (RT) throws of medicine balls weighing 5 kg while twisting the trunk. Augmentation while throwing the medicine ball was positively correlated with ball velocity (r=0.619, p<0.01), and augmentation of the medicine ball was positively correlated with torso rotation velocity at 18-27% and at 46-75% (r=0.398-0.542, p<0.05), and trunk twist velocity at 60-66% (r=0.378-0.395, p<0.05) of the second phase (from stride foot contact to instant release of the ball) during the pitching motion. In addition, pitched ball velocity was positively correlated with the velocities of pelvic rotation at 37-78% (r=0.378-0.488, p<0.05), torso rotation at 46-87% (r=0.391-0.711, p<0.05) and trunk twist at 63-83% (r=0.375-0.499, p<0.05) during the second phase of the pitching motion. These results indicate that pitchers with a larger ball velocity can use SSC movement generated by twisting the trunk, which effectively increases trunk rotation from the first half to middle of the second phase, and they can also increase trunk rotation during the second phase.