Assessment of reach-to-grasp trajectories toward stationary objects

Patients with pronounced spasticity reveal difficulties in hand opening during the approaching grasping phase. The general description and assessment procedures of reach-to-grasp movement for rehabilitation purposes is still not established. There is a necessity to develop a universal methodology to describe the approaching phase in grasping which would allow clinical evaluation of movement pathologies.

In the paper, the evaluation of approaching trajectories assessed during grasping by healthy subjects is described. The experiment, undertaken by 7 healthy volunteers, consisted of grasping three different stationary objects positioned in various poses by a robot. 3D recordings of the hand and fingertip trajectories were performed. The kinematic trajectories of the hand and finger markers were analysed in order to evaluate the reach-to-grasp movement.

The results of the kinematic analysis suggest that the reach-to-grasp movement of a healthy subject can be divided into 3 dominant phases (hand acceleration, hand deceleration, and final closure of the fingers).

The presented evaluation method can provide relevant information on the modalities the hand preshapes and approaches toward the object in order to obtain a stable grasp. The potential use of the approach for rehabilitation purposes is discussed.