The effect of choice reaction on soft-tennis forehand drives in cross (CRS) and down-the-line (DWN) shots were investigated. Six highly skilled soft-tennis players served as subjects. The authors used a two-choice reaction condition and non-choice reaction condition in the experiment, and some kinematic variables such as anatomical rotations at the upper extremity joints and upper torso movements were computed with a three-dimensional DLT method. The major results obtained were as follows:

1) Both contact point relative to the right shoulder and racket angle at impact were important factors to decide the direction of shots irrespective of the conditions. And the racket-head trajectories relative not to the right shoulder but to the contact-point during the forehands were distinguishable between CRS and DWN.

2) As the mean angles of external rotation at the shoulder joint at impact were considerably large irrespective of the conditions and shot directions, it was indicated that internal-external rotation at the shoulder joint was considered to be highly adaptive to control the racket and therefore to be involved in the mechanics to decide the direction of the shots. And wrist joint rotation was also considered to be involved in such mechanics.

3) Under the choice reaction condition, the forward lean of the upper torso at the initiation of forward swing was considerably larger in CRS compared with in DWN, on the contrary no difference was found under the non-choice reaction condition.

4) The range of pelvis and shoulder rotations during the forward swing phase were tended to be smaller in choice reaction condition than in non-choice reaction condition.

5) The forward component of the center of gravity movement tended to be restrained in DWN than in CRS.

These results indicate that contact-point relative to the body is the major factor to decide the direction of the shot irrespective of the conditions during forehand drives, and that the effects of shot direction might appear in upper extremity movements and conditions in torso movements, respectively. Therefore it is suggested that the control of the racket to the contact point during forehand drive depends on upper extremity movements, and the role of torso movements is ensuring the posture to make the racket-ball contact easily.