In this paper the authors introduce the results of the experiment analyzing the kinematic character of soft-tennis forehand drives, on the basis of a typical situation model in one-up-one-back formation with a three-dimensional DLT method. Forehand drives were executed under a two-choice reaction condition, which contrasted with a non-choice reaction condition (NCR, n=6), while for the analyzing, the choice reaction condition was divided into the repeated condition (REP, n=5) and the non-repeated condition (NRP, n=6). In case of REP, the same stimulus was repeated more than four times, but in case of NRP, the stimulus different from the immediately preceding one was presented.

The major results obtained in this investigation were as follows:

(1) In comparison of the choice reaction condition and the non-choice reaction condition, the accelerated sequences of the body differed distinctively; in the choice reaction condition the upper limb was accelerated before the trunk was.

(2) The angle of shoulder horizontal extension tended to be larger until about 0.05 sec before impact, and the height of contact-point tended to be lower in case of the choice reaction condition in comparison to the non-choice reaction condition.

(3) The contributions made by the internal rotation and the abduction of the shoulder joint to the racket-head velocity were slightly higher in case of the choice reaction condition (REP 52.9%, 10.1%; NRP 53.2%, 11.0%) than the non-choice reaction condition (NCR 49.3%, 5.4%).

(4) The contribution made by the wrist joint at just before impact tended to be higher in REP than in other conditions.

These results suggest that in order to make the ball-racket contact successful, subjects used different mechanics of the motions for accelerating the racket and employed certain strategies under choice reaction condition.

The purpose of this study was to investigate the characteristics of 1000 m race-patterns for an elite speed skaters at the World Sprint Championship 1993 in IKAHO, Japan. Twenty-eight skaters participated in men's 1000 m races were videotaped (60 fields/s) with five panning VTR cameras. Mean skating speed, skating-cycle frequency and-cycle length at twenty sections (about 50 m each) were measured. Skating speeds of both inner and outer starting lanes were quickly increased until they reached the maximal speed around 300 m marks, then slightly decreased around 700 m marks and rapidly fell down to the finish. There were close relationships between skating speeds in the second half of the races and finishing time. By using mean value of the rate of decline (%) in skating velocity defined as (1- (1^st lap time/2^nd lap time) x 100, race-pattern for all skaters were classified into two types, so that it should be suggested that small increase in skating-cycle frequency at 600 m marks is important to keep their skating speeds in the last stage of the races.

The purpose of this study was to identify the relation between the force production during take-off by ski jumpers and their performance. The force measuring system which constructed under the take-off platform was used to measure the normal forces exerted during take-off by ski jumpers. This field research was conducted in a competition “FIS Continental Cup Asia Series NTT Cup Summer Jumping Games” in 1996.

Three variables were analyzed as follows: the average forces (F'_6-0m), the peak force value (Fz_peak) and the net impulse (I_6-0m) of the force measured from the last 6 m of the take-off platform. These variables were significantly correlated to the distance of ski jumping. Also these variables were compared between two groups: the 1 - 10 placers (longest 10) and the 41 - 50 placers (shortest 10). All the variables obtained by the longest 10 group showed significantly higher value than those of the shortest 10 group. These results indicate that the force production during the take-off has some effects on the ski jumping performance. It was found that the force curves obtained from the same subject were closely similar to each other. Comparison was conducted between two ski jumpers about their ways of force production. These two ski jumpers had same amount of the impulse of the force, but their ways of force production were very different.