The Control Strategy for Degrees of Freedom in Remote Prehension with a Tool

Constructing movement couplings is essential for decreasing degrees-of-freedom for a compound movement that requires coordination over a multiple segments. Angular movements of joints in the upper limbs are examined, the pattern of movement couplings between prehension performed with the hands (natural prehension) and with a simple grasper held in the hands (remote prehension). In remote prehension, the shoulder and elbow joint are tightly associated with a clear in-phase joint to joint movement; the elbow and wrist display both antiand in-phase movements due to the change of initial configuration of the upper limb when holding a tool. In contrast, the shoulder-elbow bond is mixed in natural prehension, but the elbow and wrist bond is predominant with an anti-phase pattern. With diversity for joint couplings, the movement consistency of the hinge is preserved with relatively smaller path variability. Results support the end-point control notion, i.e. movement is controlled by extrinsic coordinates close to the end-effectors of the movement system.