Trunk-assisted prehension: Specification of body segments with imposed temporal constraints

The authors used a trunk-assisted prehension task to examine Intersegment c oordination. Participants (N = 7) reached to grasp an object placed beyond full arm extension, thus requiring trunk flexion to achieve the target obje ct, under 4 varying temporal constraints. Kinematic analyses were performed in which the motions of the arm, the trunk, and the endpoint were characte rized. The spatial trajectories and the segments' peak velocity data reveal ed that under high temporal constraints the arm was more responsible for en dpoint motion than the trunk, whereas in the unconstrained condition the tr unk was more involved. in addition, the arm exhibited a decline in spatial variability toward the end of the movement in all conditions, whereas the t runk did not. The present study is the first to show that when temporal dem and is increased for a trunk-assisted prehensile task, the arm plays a larg er role than the trunk in the transport of the hand to the object. The data also suggest that the arm participates in the fine accuracy control of the reach, whereas the trunk does not.