Research ReportThe trunk as a part of the kinematic chain for reaching movements in healthy subjects and hemiparetic patients

The aims of this study were first to further assess the role of the 3D trunk angular rotations as part of the kinematic chain for seated-reaching movements within arm's length in a large 3D workspace in healthy subjects and second, to assess if these degrees of freedom participate in the compensatory strategy in hemiparetic patients. Ten healthy subjects, eight patients with right, and eight patients with left hemiparesis following stroke were included. They performed seated reaching movements at a comfortable speed to nine targets positioned in a large 3D workspace within arm's length. An electromagnetic system was used to record kinematics of the trunk and hand. Trunk flexion, lateral flexion and torsion were analyzed as a function of target direction, distance and height. In both healthy subjects and patients, all three trunk rotations participated in the reaching movement (except for near targets in healthy subjects). Trunk flexion was greater in patients but followed a similar pattern to healthy subjects. Trunk torsion was more influenced by target distance in healthy subjects while in patients it was greatly influenced by direction. Trunk lateral flexion was similar between groups. Comparing the two patient groups, there was greater flexion to the external targets in the RHD group and different strategies in the use of torsion between groups. 3D trunk rotations thus seem to be tuned to the distance and direction of the target in the workspace in both healthy subjects and stroke patients for reaching movements within arm's length.

Research highlights► 3D trunk motion participates in reaching within arm's length in healthy subjects. ► Trunk flexion is increased in stroke patients during reaching movements. ► Trunk flexion varies similarly across targets in stroke and healthy subjects. ► Trunk torsion is related to target distance in healthy subjects. ► Trunk torsion is related to target direction in stroke patients.