In competitive sports such as judo and sumo, in which opponents wrestle with each other, evasive actions by one opponent who has predicted the move of the other can lead to the toppling of a lager opponent. This study examined muscle activities associated with known and unknown perturbation induced by a forward bilateral pushing movement. Participants stood upright and voluntarily pushed a lever at a maximal strength in two tasks: one where the lever was free to be moved by the participant (perturbation; movable task) or the other where it was blocked by the experimenters (stationary task). The degree of predictability of the lever’s mobility was manipulated by the experimenters. Displacement of body segments, electromyography and pushing strength observed during each task were recorded, and the following main results were obtained. Under condition that the participant did not know the movement of the lever in advance, preliminary activity for perturbation was observed with a start of the pushing movement. However, after the timing of perturbation onset, the muscle activity corresponding to each task was found to be within 100 ms. Given these results, it is suggested that the movement is initiated based on the motor commend that corresponding to perturbation under conditions of uncertain prediction, and after the movement is started, it is then modified with a short latency in accordance with the motor command that corresponds to the movement of the lever.

The purpose of this study was to describe the angular momentum of the runner's body about the center of mass (CM) during the maximum-effort sprinting along a curved runway. Ten male collegiate sprinters were asked to sprint along the 2nd lane on an official 400m track. The performances were recorded with four high speed cameras. The DLT algorithm was used for 3D reconstruction and the angular momentum of the whole body about the CM was calculated. The results showed that the runner’s body possessed throughout the stride cycle an inward-directed component (33.5×10^–3±2.8×10^–3s^–1) of angular momentum and that the head and torso possessed a cranially-directed component (0.4×10^–3±0.2×10^–3s^–1). The antero-posterior component of angular momentum changed its sense from forward- to backward-direction during the right ground contact phase. These results indicate (a) that the runner's head and torso changed its orientation continuously throughout the support- and the airborne-phases to face forward along the curved runway and (b) that the angular impulse exerted on the body during the right ground contact phase changed the direction of the forward somersaulting angular momentum of the whole body possessed primarily by the limbs, so that the runners could maintain the plane of the limbs' rotary motion in the tangential direction to the curved runway.

The purpose of this study was to examine the influence of swing angle and rolling angular velocity of bat on batted ball. Three-dimensional finite element method was used to construct a model of baseball and wooden baseball bat, and impact between them was simulated with various conditions. The angle from the horizontal of the bat swing velocity immediately before impact (defined as swing angle) was set at –10, 0, 10, 20 deg, and the rolling angular velocity of the bat was set at 0, 1000, 2000 deg/s. The velocity and the angular velocity of the batted ball immediately after impact, and the flight distance were determined for the four swing angles and three rolling angular velocities. The simulation model was validated by comparing the simulation outcome with experimental data obtained from free-batting practice performed by collegiate baseball players. The result showed that the maximum flight distance was gained with swing angles of 10 and 20 deg. Flattened trajectory and shorter flight time were recorded for the bat swing angle of 10 deg. The rolling angular velocity was found to make minimal influence to the flight distance, but an increase in the rolling angular velocity caused the ball trajectory to be flattened and corresponding flight time to be shorter.