Similar planning strategies for whole-body and arm movements performed in the sagittal plane.

The present paper looks for kinematic similarities between whole-body and arm movements executed in the sagittal plane. Eight subjects performed sit-to-stand (STS) and back-to-sit (BTS) movements at their preferred speed in the sagittal plane. Kinematics analysis focused on shoulder motion revealed that STS was composed of a straight, forward displacement followed by a curved, upward displacement while BTS was characterized by a curved, downward and straight, backward displacement. Curvature of the upward displacement was significantly greater than the downward one. Analysis of shoulder-velocity profiles showed that movement duration was significantly longer for BTS compared with STS and that the shape of the velocity profiles changed when subjects performed an STS compared with a BTS movement. Velocity profiles of the upward and downward displacements also differed; the relative acceleration duration (acceleration duration divided by movement duration during the vertical motion) was smaller for the upward compared with the downward displacement. The present results are in accordance with previous findings concerning the execution of vertical arm movements and suggest that the CNS uses similar motor plans for the performance of arm and whole-body movements in the sagittal plane.