This study aims to elucidate what factors take a major role to classify skilled and unskilled performers on power clean(PC) athletic motion. The subjects are twelve healthy males divided into two groups, six skilled and six unskilled with the value of “PC 100% 1RM/body weight” exceeding or not. The joint angle of the subjects' lower limbs during the PC of which intensity is set at 70% are recorded accompanied by measuring the concurrent ground reaction force. The joint torque and power are calculated from the obtained data and analyzed to evaluate a skilled performance. Our results are as follows :

1)In the skilleds' motion, the knee flexion-extension occurs with concurrently decreasing the ground reaction force, which suggests the skilled have acquired “double knee bent (DKB)” that induces so-called stretch-shortening cycle (SSC).

2)Joint angular velocity and joint torque show that skilled's muscles of lower limbs achieve a pre-contraction caused by DKB, which means the stored elastic energy is reused during the SSC. It can be explained by mechanical energy flow between neighboring joints on lower limb. The skilled shows relatively large energy flow than the unskilled.

3) Furthermore, due to transferring the energy effectively, the skilled can exert large joint torque and power. It indicates that elastic energy stored in the DKB motion accompanied by the SSC may be useful for instantaneously generating the large joint torque and joint torque power during PC.

The purpose of this study was to investigate the contribution of impact location and various parameters describing bat swing to the kinetic energy of the batted ball in baseball batting. Ten collegiate baseball players participated in this study. Each player performed 50 trials of free-batting, aiming at hitting a line-drive toward the center field. Behavior of the ball impact was recorded with two high-speed cameras. All trials in which the batted ball travelled toward the center field, including grounders, line-drives and fly balls, were used for the analysis. From the video-recordings, impact location relative to the “sweet spot” was measured to represent the accuracy of impact and various kinematic parameters were measured to describe the bat swing. For each subject, a step-wise multiple regression analysis was conducted to predict the kinetic energy of the batted ball from impact location and swing parameters. The results showed that the within-subject variance in the kinetic energy of the batted ball was accounted for by the impact location (48 ~ 76 %) and the swing parameters (0 ~ 28 %). No correlation was found between bat speed and impact location. These results suggest that the impact location explains to a large extent of the within-subject variance in the kinetic energy of the batted ball and that the speed-accuracy trade-off does not exist in baseball batting performed by collegiate players.