Investigating optimal technique in a noisy environment: application to the upstart on uneven bars.

The upstart is a fundamental skill in gymnastics where it is used to transfer a gymnast from a swing beneath the bar to a position above the bar. The aim of this study was to optimize the technique in the upstart on the uneven bars in order to determine the underlying control strategy used by gymnasts. A previous attempt based on minimizing joint torque had failed to find a satisfactory solution without forcing the joint angle histories to pass through a "via-point" (Yamasaki, Gotoh, & Xin, 2010). Using a computer simulation model of a gymnast and bar, the technique (joint angle histories) used in the upstart was optimized under three different criteria: minimizing joint torque, minimizing joint torque change and maximizing success in the presence of movement variability. The third optimization introduced "noise" into the joint angle time histories based on measurements of kinematic variability. All three optimizations were started from the technique used by a gymnast competing in an Olympic Games uneven bars final. Root mean squared (RMS) differences between the recorded and optimal joint angle time histories were computed. The two optimizations based on minimizing joint torque diverged from the gymnast's technique. However, the technique based on maximizing the number of successful performances in a noisy environment remained close to the gymnast's technique. It is concluded that the underlying strategy used in the upstart is not based on minimization of joint torque; rather, it is based on ensuring success in the task despite the inherent variability in technique. Gymnasts develop techniques that are able to cope with the level of kinematic variability present in their movements.