Kinematics of point-to-point finger movements.

The goal of this study was to examine the characteristics of planar fingertip movements with respect to the hand. Ten subjects with no known neuromuscular impairments performed a series of point-to-point movements with their dominant index fingertips. Subjects were instructed to move between five pairs of targets within the workspace of the index finger in each direction, for a total of ten separate movement tasks. We hypothesized that the trajectories with respect to the hand of these movements would exhibit curved paths contrary to the findings of similar hand path studies. The ratio of the path taken to the straight-line distance between the two targets was dependent upon the movement task (P < 0.01), as was the mean residual between the actual and straight-line paths (P < 0.001). For selected pairs of targets, these values were significantly different for the two opposing movement directions between a given pair of targets. This directional dependence of the curvature of the chosen finger-only trajectory observed in the initial protocol is incompatible with motor planning based solely on kinematic constraints, instead mechanical properties of the finger are likely incorporated.