The purpose of this study was to identify mechanisms to increase bat head speed in baseball batting, from the view-point of kinetics. The batting motion of ninety-nine amateur baseball players was recorded with a motion capture system, and the kinematics and kinetics of the bat were analyzed. The bat's rotational power increased with the torque exerted on the bat's grip. However, torque and rotational power declined just prior to impact. It can be interpreted that these declines arise from a decrease in torque exerted by the wrist's periarticular muscles as the bat's rotational velocity increases (muscle force-velocity relationship). On the contrary, the bat's translational power increased just prior to impact. Judging from the relationship between the force exerted on the bat's grip in the direction of the bat's long axis and the bat head speed, the bat's translational power seems to depend on the bat's grip velocity in the direction of the bat's long axis. It was revealed that the bat's energy, by the application of rotational and translational power at diŠerent times, contributes to an increase in bat head speed in baseball batting.

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AbstractThe purpose of this study was to evaluate the generation, absorption and transfer of mechanical energy during baseball batting, focusing on the lower extremities and torso. The batting motion and ground reaction forces acting on each foot of 79 amateur baseball players were recorded using a motion capture system and 2 force plates. The joint forces and joint torques were calculated using inverse dynamics. In addition, the mechanical powers as a function of each joint torque were calculated to assess the generation/absorption of mechanical energy. The mechanical powers as a function of joint forces and joint torques acting on each segment were calculated to assess the transfer of mechanical energy. The main results were as follows: 1. In the phase from contact of the stride foot to the peak lower torso rotational velocity (lower torso acceleration phase), the mechanical energy was generated and ‰owed into the lower torso as a function of hip joint torque.2. In the lower torso acceleration phase, the mechanical energy ‰owed out from the lower torso to the upper torso as a function of torso joint torque.3. In the phase from the peak lower torso rotational velocity to impact (swing phase), the mechanical energy was generated and ‰owed into the upper torso as a function of torso joint torque.4. In the swing phase, the mechanical energy of the bat increased rapidly, and this amount of change was signiˆcantly correlated with the bat head speed at impact.5. Though the analysis phase, the change in the mechanical energy of the torso was small. These results suggest that both hip joints generate mechanical energy and that the torso acts as a pathway of mechanical energy during baseball batting. In addition, the transfer of mechanical energy from the torso to the upper extremities and the bat contributes to increasing the bat head speed at impact.

The purpose of this study was to investigate motion factors in female javelin throwers during success and failure trials from a biomechanical standpoint. Fourteen throwers who participated in the Japanese Women's Javelin Championships Final were investigated during both success trials and failure trials and the results were compared. The success trial was set as the best record and the failure trial as the worst record. Timing points of throwing motion were set at right foot contact (R-on), left foot contact (L-on) and javelin release (REL). The main results were as follows; 1) There was no significant difference in approach velocity between the success and failure trials. 2) In the success trials, peak speeds of the right shoulder, elbow joint and javelin were higher than those in the failure trials. 3) In the success trials, the left rotation velocity of the shoulder angle was larger than that in the failure trials just after L-on. 4) In the success trials, the forward rotational velocity of the trunk was larger than that in the failure trials just after L-on. 5) In the success trials, the throwers maintained a more extended position of the left knee angle than in the failure trials between L-on and REL. These results revealed that superiority or inferiority for female javelin throwers at the same competition level was determined not by the approach velocity, but by the blocking motion of the left leg. Although the importance of this left leg blocking motion has been reported many times in previous studies of throwers with different performance levels, it has been shown here to play an important role in the success of individual performance.

This study aimed to determine the minimum required initial velocity to hit a fly ball toward the same field (left-field for right-handed batters), center field, and opposite field (right field for right-handed batters). Six baseball players hit fastballs launched by a pitching machine. The movements of the balls before and after bat-to-ball impact were recorded using two high-speed video cameras. The flight distance was determined using a measuring tape. Seventy-nine trials were analyzed, and the minimum required initial velocities of batted balls were quantified to hit balls 60, 70, 80, 90, 100, 110, and 120 m in each direction through regression analysis. As a result, to hit a ball 120 m, initial velocities of 43.0, 43.9, and 46.0 m/s were required for the same field, center field, and opposite field, respectively. The result provides a useful index for batters to hit a fly ball in each of the directions.