A three-dimensional (3D) videography study was performed to clarify the mechanical effects of a change of pitching motion from an overhand throw (OH style) to a three-quarter throw (TQ style). Two collegiate pitchers (subjects A and B) who normally used the OH style participated. They were requested to change their original OH style into the TQ style. To do this, they were subjected to a one-year skill training program based on biomechanical principles and on knowledge such as the stretch-shortening cycle theory, muscle force-velocity relationship, and the motions of skilled pitchers (e.g., shoulder positioning at 90 degrees of abduction-adduction during the acceleration phase). Four pitches for subject A (two in pre-training, one during training and one in post-training), and three for subject B (one each in pre-training, training and post-training) were videotaped with the 3D DLT procedure using two high-speed cameras, and then analyzed. We then examined the mechanical differences between pre- and post-training. The speed of the ball at release increased progressively with every successive pitch for both subjects (Subject A : 1st : 130.3km/h ; 2nd : 133.2km/h ; 3rd : 135.7km/h ; 4th : 142.2km/h. Subject B : 1st : 131.0km/h ; 2nd : 135.0km/h ; 3rd : 139.3km/h). The pitching styles of both subjects changed from their original OH style to the TQ style, both qualitatively and quantitatively. The time-dependent patterns and peak values of the angular velocities of shoulder internal-external rotation and elbow flexion-extension of the throwing arm did not change very much. However, the peak value of the angular velocity of shoulder internal rotation occurred immediately after ball release for the OH style, while for the TQ style it occurred at ball release. As a result, the angular velocity of elbow extension at ball release was larger in the OH style than in the TQ style. On the other hand, the angular velocity of shoulder internal rotation at ball release was larger in the TQ style than in the OH style. These findings suggest that the increase in the speed of the ball is dominated by elbow extension in the OH style, and by shoulder internal rotation in the TQ style.