We aimed to investigate the generation and absorption of mechanical energy by the lower limb joints during the arm support phase of kicking pullovers. Thirteen men performed kicking pullovers, and the kinetics and kinematics of the hip, knee, and ankle joints were calculated between takeoff and upside position using a sagittal-plane, 10-segment, rigid body link model. The hip joint of the support leg generated the most energy by flexion torque and large flexion velocity of 331±66 deg/s. This joint was markedly extended at takeoff, which might have allowed for the large angular velocity and the expansion of the impulse by the ground reaction force before takeoff. These observations suggest that a series of movement skills including extension of this joint toward takeoff and rapid flexion of it immediately after takeoff is an important factor to achieve kicking pullover. The hip joint of the swing leg absorbed energy by exerting extension torque, suggesting that a part of the kinetic energy of the swing leg at takeoff was transferred to the trunk with this torque to facilitate the upward migration and backward rotation of the trunk. Hence, further studies on the energy transfer by the lower limb joints are required.

In baseball hitting, the skill of the batter required to make a hit is high bat-head speed immediately before impact, accurate impact, and compact swing. Meanwhile, batting performance is affected by not only the batting techniques but also the bat mass and bat grip position. In addition, the influence of bat mass in youth players is thought to be greater than that in adult players. The purpose of this study was to investigate differences in the parameters of batting performance between the use of different bats at the moment of inertia (light or heavy bat) and normal or choked-up grip, and to provide the optimum bat and grip position for each batter. Fifty-seven youth (elementary and junior high schools) baseball players were asked to hit a baseball by using four types of bats. The hitting movement was recorded by using two high-speed cameras (1000 fps). Batting performance was evaluated by using eight parameters, including the speeds of the batted ball and bat, the bat trajectory, and the impact accuracy. Analysis of the principal component was conducted to find the condition maximizing each parameter. In 39 (68%) of the 57 subjects, the lightest bat was selected as the optimum condition. Of these subjects, 27 chose the choked-up grip condition. The main reasons for choosing the light bat and choked-up grip as optimal conditions were the increase in the angular velocity of the bat, the shortened travel distance of the bat head, and the shortened swing time. On the other hand, the optimal condition varied among players, and the parameters changed with the kind of bat chosen by each player. Meanwhile, when comparing the bat based on the ideal batted ball speed which is not influenced by impact accuracy, the heaviest bat was chosen from 9% of elementary school students. However, among junior high school students, the heaviest bat was chosen from 64% of total players. In conclusion, if the players choose a bat for the purpose of maximizing the hitting performance, youth players in the range of junior high school age, depending on their aim, can benefit from using the heavy bats whereas younger elementary school players tend to find the use of the light bat preferable regardless of their aim.