On the role of postural synergies for grasp force generation and upper limb motion control

Although human movements are extremely complex, our nervous system is able to implement effective control strategies, leveraging on a generalized simplification approach. Several works described this behavior within the framework of synergies, which can be regarded as basis ingredients for motion generation through dimensionality reduction. Focusing on hand kinematics, this concept allowed to dramatically improve our understanding of the neuro-physiology of hand motor system, offering effective mathematical tools to identify pathological deviations from the physiological case. At the same time, these observations have found a fertile application field in robotics, suggesting simple yet effective manners to design and control artificial systems, with a reduced number of actuators or inputs. However, while much has been said about kinematic hand synergies and their implications for engineering, there are still open issues to tackle. Solving these issues could give better insights on the synergistic organization embedded within the human body, finally impacting the future development of robotic devices. In this paper, we will explicitly focus on the role that hand postural synergies play for grasp force control, and on preliminary observations on a synergy-based organization for upper limb motion generation. Applications of these neuroscientific findings for devising a principled simplification approach in assistive and rehabilitation robotics are finally discussed.