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Eric J. Sprigings and Robert J. Neal

The purpose of this study was to examine whether, in theory, the clubhead speed at impact could be increased by an optimally timed wrist torque, without jeopardizing the desired club position at impact. A 2-D, three-segment model comprising torso, left arm, and golfclub was used to model the downward phase of the golf swing. Torque generators that adhered to the activation and force-velocity properties of muscle were inserted at the proximal end of each segment. Separate simulations were performed, with the wrist joint generator enabled then disabled. The results from these simulations showed that significant gains in clubhead speed (≈9 %) could be achieved if an active wrist torque was applied to the club during the latter stages of the downswing. For a swing that produced a clubhead speed of 44 m/s (≈99 mph), the optimal timing for the activation of wrist torque occurred when the arm segment was approximately 30° below a horizontal line through the shoulder joint. The optimal activation time for the joint generators was very much dependant on the shape of the torque profiles. The optimization process confirmed that maximum clubhead speed was achieved when the torque generators commenced in sequential order from proximal to distal.

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Shohei Shibata, Yuki Inaba, Shinsuke Yoshioka and Senshi Fukashiro

identified by peak time. However, whether proximal-to-distal segmental sequence occurs from wrist to fingers was not examined. Thus, the second objective of this study was to examine the central nervous system’s (CNS’s) timing control between the wrist torque and finger torque. Probably, for accelerating the

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Maurice R. Yeadon and Grant Trewartha

The goal of this study was to investigate the control strategy employed by gymnasts in maintaining a hand balance. It was hypothesized that a “wrist strategy” was used in which perturbations in the sagittal plane were corrected using variations in wrist flexor torque with synergistic shoulder and hip torques acting to preserve a fixed body configuration. A theoretical model of wrist strategy indicated that control could be effected using wrist torque that was a linear function of mass center displacement and velocity. Four male gymnasts executed hand balances and 2-dimensional inverse dynamics was used to determine net joint torque time histories at the wrist, shoulder, and hip joints in the sagittal plane. Wrist torque was regressed against mass center position and velocity values at progressively earlier times. It was found that all gymnasts used the wrist strategy, with time delays ranging from 160 to 240 ms. The net joint torques at the shoulder and hip joints were regressed against the torques required to maintain a fixed configuration. This fixed configuration strategy accounted for 86% of the variance in the shoulder torque and 86% of the variance in the hip torque although the actual torques exceeded the predicted torques by 7% and 30%, respectively. The estimated time delays are consistent with the use of long latency reflexes, whereas the role of vestibular and visual information in maintaining a hand balance is less certain.

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Robert J. Neal and Barry D. Wilson

Three-dimensional kinematics and kinetics for a double pendulum model golf swing were determined for 6 subjects, who were filmed by two phase-locked Photosonics cameras. The film was digitally analyzed. Abdel-Aziz and Karara's (1971) algorithm was used to determine three-dimensional spatial coordinates for the segment endpoints. Linear kinematic and kinetic data showed similarities with previous studies. The orientation of the resultant joint force at the wrists was in the direction of motion of the club center of gravity for most of the downswing. Such an orientation of the force vector would tend to prevent wrist uncocking. Indeterminate peak angular velocities for rotations about the X axis were reported. However, these peaks were due to computational instabilities that occurred when the club was perpendicular to the YZ plane. Furthermore, the motion of the club during the downswing was found to be nonplanar. Wrist uncocking appeared to be associated with the resultant joint torque and not the resultant joint force at the wrists. Torques reported in this study were consistent with those reported by Vaughan (1981).