The purpose of this study was to clarify the transition of playing time in tennis. To analyze about playing time in tennis, we use the computerized scorebook for tennis developed by the authors. Six matches, men's singles final of Wimbledon held in 1980, 1981, 1993, 1994, 2004 and 2005 were analyzed. The results about the transition of playing time in Wimbledon men's final were obtained as follows. Time duration per point was longest on 2000s (3.99±4.00 sec), and was shortest on 1990s (2.70±3.22 sec). Rally length was also longest on 2000s (4.1±3.0 shots), and was shortest on 1990s (3.0±2.1 shots). The inter-point time was shortest on 2000s (19.10±4.83 sec). These results showed that playing time became longer and rest time became shorter on 2000s matches. Players' physical ability was highly required on 2000s matches. The time duration of 1st service shot was shortest on 1990s (0.69±0.07 sec). The time duration of ground stroke shot was shortest on 2000s ( 1.34±0.31 sec). First service shot became faster from 1980s to 1990s, ground stroke shot became faster from 1990s to 2000s. These results were based on the changes of rule (e. g. ball regulation, inter-time rule), the innovation of racket technologies and the changes of players' play-style. The computerized scorebook developed by the authors was able to analyze about playing time in tennis.

The purpose of this study was to identify kinetic characteristics of the support leg due to fatigue during the side-jump test in speed skaters. Ten male skaters performed the 7O-second-maximal effort side-jump test on a tartan track in the laboratory; two synchronized high-speed video cameras (250 fields/s) were used to record their performance using the DLT technique. Ground reaction forces (GRF) of the right leg were determined using the force platform (500 Hz). The GRF and three-dimensional coordinates of the segment endpoints were collected over 70 seconds to calculate the right support leg kinetics during the first and second halves of the test, at 5 and 65 seconds, respectively, using an inverse dynamics approach. During the first half, the absolute work done by hip torque was significantly greater than those of the knee and ankle torques. This indicates that great energy exertion by the hip muscles is a characteristic of the side-jump. During the second half, there was decreased knee extension torque and power at approximately 80% stroke. Thus, minimizing the decrease in the torque and power under fatigue conditions would be an important factor for endurance training of the side-jump.

In soccer, the topspin-kick skill, which deflects the trajectory of a ball vertically in a direct free kick, has recently attracted widespread attention. The purpose of this study was to clarify the mechanism of the topspin-kick motion by focusing on the fact that the rotational axis of a ball which generates topspin leans to the left. We instructed 7 subjects skilled in soccer to kick the ball with their right foot with various angles of rotational axis. The shooting motions were recorded using an optical motion capture system. The following results were found using multiple linear regression analysis applied to the variables of the impact phase.

1) Movements of the foot to impact

The main factors are to turn the swing direction of the foot upwards to impact and to turn the toe upwards to impact to make the rotational axis of the ball lean to the left.

2) Motions of the kicking leg

To position the greater trochanter of the kicking leg backward has a beneficial effect on turning the swing direction of the foot upwards to impact. Also, dorsiflexion of the ankle joint and inclination of the shank of kicking leg to the left have a beneficial effect on turning the toe upwards to impact.

3) Motions of the supporting leg

With individual differences, the motions of the supporting leg to make the rotational axis of the ball lean to the left include planter flexion of the ankle joint, flexion of the knee joint, inclination of the shank to the left, keeping the pivoting foot further to the side from the ball and increasing the approach angle.

It is concluded that these results are expected to give useful information for soccer players to improve their topspin-kick skill.