Strategies for coordinating balance control and orientation of head-trunk axis during leg movement

Summary form only given. When a voluntary movement is performed, the displacement of the moving segments toward a goal is only one aspect of the motor act. Other goal-directed actions are achieved simultaneously, which is necessary for the accuracy of the performance. Leg raising is presented as an illustration of a task with multiple goals achieved at the same time. The main goal is the displacement of the leg toward a given position. Several secondary goals can be identified. One of them is the vertical orientation of head and trunk axis, the other the stabilization of the center of gravity projection onto the ground after the initial displacement of the CG toward the supporting leg. These two secondary goal-directed actions, related to vertical orientation of head and trunk and to equilibrium control, respectively, are achieved through a coordinated control that occurs in parallel with the main movement. For each of these coordinated controls, the authors discuss which reference value is regulated and how, why, and where it is regulated.<>