Submovement changes in goal-directed and non-goal-directed ankle movements using pediAnklebot

The aim of the study is to compare motor performance of goal-directed vs. non-goal-directed dorsiflexion ankle movements, for exploring how the central nervous system (CNS) plans movements that require the optimization of different kinematic parameters, which are the movement accuracy and speed. Measurements were performed using the pediAnklebot robot on 10 normally developed children. The protocol consisted of two tasks (i.e. goal-directed and non-goal-directed), each one composed by 20 movement trials. Subjects performed the protocol with both dominant and non-dominant leg. In the goal-directedtask, the subject was instructed to control a pointer in the monitor, by means of the ankle dorsiflexion movements, to reach a virtual target with a straight trajectory. In the non-goal-directed task, instead, the subject was asked to perform the same movement aiming at fast kicking a virtual ball. Ankle angular displacements were gathered by encoders embedded in the robot. Ankle motor performance was evaluated by means of both kinematic (duration of the movement, lateral deviation, position error and speed metric) and submovement indices (number, duration and rate). Comparing the two tasks, no differences were found in kinematic parameters, whereas differences were highlighted in submovement features. From the results, it emerges a higher capability of the central nervous system in planning non-goal-directed movements than goal-directed ones, even if the smoothness and accuracy of the trajectory have not been altered by the different required task. These findings provide an important starting point to understand how the CNS changes the motor planning to face different request in the execution of the movement, such as accuracy or speed optimization.