The purpose of this study was to examine quantitatively the relationship between tibial torsional loading and running speed. Six male subjects were asked to run at different speeds (2.0, 3.5, and 5.0 m/s). Data were collected with two high-speed cameras and a force platform. Net axial moments acting at both ends of the tibia during stance phase were calculated using inverse dynamics. The tibial torsional moment was determined from the quasi-equilibrium balance of the net axial moments. The maximum value of the tibial torsional moment (y) was positively correlated with running speed (x) (y = 0.343+0.253 x ; r = 0.998, p < 0.05), although considerable inter-individual differences could be found. Multiple regression analysis implied that these inter-individual differences could depend substantially on the frontal motion of the shank.

The purpose of this study was to analyze and compare the kinematics of two tennis forehand ground strokes, cross-court stroke and straight shot stroke, for world-top female tennis players in official games. Forehand strokes of the players at Japan Open '96 and '97 and Fed Cup (Japan vs Germany) held in Tokyo were videotaped with two high speed VTR cameras operating at 200 Hz. Analyzed world-top female tennis players were S. Graf, A. Huber, K. Date, A. Frazier, N. Sawamatsu, A. Sugiyama, and N. Kijimuta. They all were right-handed. Three dimensional coordinates of body landmarks, the racket and ball were obtained with a DLT method. Angular kinematics of the upper limb, the trunk and the racket, and the impact parameters were calculated.

The results were summarized as follows:

1) In the cross-court stroke, the racket tip at the impact was positioned more forward (p < 0.001), and the impact position was nearer (p < 0.05) and more forward (p < 0.001) relative to right shoulder than those of the straight shot stroke.

2) Pre-impact racket maximum velocity and post-impact ball velocity were significantly greater in the cross-court stroke than in the straight shot stroke (p < 0.001, p < 0.05).

3) In the cross-court stroke, the extension of the elbow joint before the impact, the snap motion of the wrist joint just before the impact and the forward rotation of shoulders during the forward swing were greater than those of the straight shot stroke (p < 0.05). The horizontal adduction of the shoulder joint before the impact was greater in the straight shot stroke than in the cross-court stroke (p < 0.05).

4) There were two patterns of change in the shoulder rotation angle. In pattern 1 shown by S. Graf, A. Huber and K. Date, the shoulders were rotated more forward just before the impact in the cross-court stroke than in the straight shot stroke. In pattern 2 shown by A. Frazier, N. Sawamatsu, A. Sugiyama and N. Kijimuta, the shoulders in the straight shot stroke were kept in backward position than those of the cross-court stroke during the forward swing.

These results indicated that the racket angle at impact, the impact position and the racket velocity just before the impact were critical factors to determine the direction of the ball struck in ground stroke. The motions of the trunk and the arm which controlled these impact parameters were the snap of the wrist joint, the flexion/extension of the elbow joint and the horizontal adduction/abduction of the shoulder joint before the impact and the forward rotation of shoulders during the forward swing.