2009 Volume 22 Issue 12 Pages 399-406
While the kip movements of expert gymnasts have been explained under the minimum torque-change criterion with assumption of a via-point, the meaning of the via-point has been unclear. On the other hand, expert gymnasts say that their movements are associated with effortless skill to achieve a task, in comparison with a movement without the via-point. We consider an integral of square of joint-torques as the effort cost, in addition to the commanded torque-change cost, and propose two approaches to reproduce the kip movement as follows: 1) a combined criterion that minimizes weighted sum of the torque-change and effort costs without assuming via-points, and 2) a hierarchical criterion that allocates via-points such that the effort cost of whole movement is minimized. The results of numerical analysis suggest that both the approaches can improve predictions of the kip movement compared with the results under the minimum torque-change model alone.