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.
Maurice R. Yeadon and Grant Trewartha
Wen-Yen Tseng, Ghazi Rekik, Chia-Hui Chen, Filipe M. Clemente, Pedro Bezerra, Zachary J. Crowley-McHattan, and Yung-Sheng Chen
Ball in the hands and listen for the stop command Ball in the hands and watch for the stop command Dribble with the ball and listen for the stop command Skating jumps Learning how to land Ball in both hands Balancing with the ball in 1 hand Dropping the ball onto the ground Dynamic balancing with ball