In many sports movements, effective use of mechanical energy is essential to achieve a good performance, as well as the generation of a great amount of mechanical energy. The purpose of this study was to investigate the effects of the technical training of a medicine-ball backward throwing on the throwing motion and mechanical energy flows in the body segments. Twelve males were participated in the training session of two days to improve the throwing distance and throwing technique. In the training session, the subjects were given the feedback information of the results, VTR images on a monitor TV and instruction based on the analysis of good throwers' motion. The subjects were videotaped with a high-speed video camera and ground reaction forces were measured with a Kistler force platform at pre- and post-training sessions. Joint forces, joint torques, joint force powers, segment torque powers, and mechanical works were calculated to evaluate mechanical energy flows with kinetic data obtained in a two dimensional motion analysis.

After the technical training, the throwing distance and translational kinetic energy of the ball at the release increased significantly (p<0.05). However, the mechanical works done by the joint torques showed no significant changes. These results indicate that the throwing technique which effectively converts the mechanical energy of the body to that of the ball was improved due to the technical training. A remarkable change after the technical training was found in the increase in the mechanical energy flow from the trunk to the arms via the shoulder joint forces. This was caused by the increase in the velocity of the shoulders, which resulted from the improvement in the motions of the trunk and legs. These results suggest that biomechanical effects of the technical training can be evaluated through the investigation of mechanical energy flow patterns and the related motions.

Reaction time was measured during simultaneous elbow flexion and hand grip contractions in 14 subjects. The results were summarized as follows:

1) The hand grip in the simultaneous condition showed a longer reaction time (RT), while no difference was found in RT for the elbow flexion. Premotor time (PMT) was increased both in the hand grip and elbow flexion. Motor time (MT) of the elbow flexion revealed a decrease, but no difference was found in MT of the hand grip.

2) Elbow flexion in the simultaneous condition exhibited decrements in peak force and maximum rate of force in crease, while no changes were observed in the hand grip.

3) Irrespective of whether the EMG onset of a distal muscle (flexor digitorum superficialis) was earlier than a proximal muscle (biceps brachii) or vice versa, the onset of the force was earlier for the proximal elbow flexion than the distal hand grip.

From these results, it is suggested that the increase of PMT and the force decrease in the elbow flexion during simultaneous condition are caused by some mechanism of central nervous system, while the earlier force onset of the elbow flexion even though the EMG started earlier for the distal muscle are due to the function of multiarticular muscles associated with both distal and proximal joint movements.