The purpose of this study was to investigate whether the speed of a thrown ball and differences in the effect of training in junior and senior high school baseball fielders at different developmental stages would be influenced by stretch-shortening cycle (SSC) training and resistance training. The subjects were classified into three groups: a SSC training group (dumbbell fly and medicine ball twist toss), a resistance training group (bench press and shaft twist), and a control group. Training was continued for three sessions per week for seven weeks. Moreover, the subjects performed purely concentric throw (CT) and rebound throw (RT) with medicine balls horizontal to the shoulder and body trunk twist movement, and the throw-index (CT: CT-index, RT: RT-index) and prestretch augmentation (Augmentation) were calculated.
The results were as follows: 1) The thrown ball speed increased significantly with SSC training in both the junior and senior high school baseball players. 2) The rate of increase in augmentation was higher in the junior than in the senior high school players. 3) The thrown ball speed increased significantly in the junior high school players who undertook resistance training, but not in the senior high school players. 4) The RT-index increased significantly in the junior high school players who undertook resistance training. 5) Augmentation was not increased significantly in the junior or senior high school players who undertook resistance training. These results suggest that the speed of a thrown ball increased significantly in junior and senior high school baseball players who undertook SSC training, and in junior high school players who undertook resistance training group. In addition, it was clarified that the effect of training differed according to developmental stage.